23.3. MySQL Connector/J

MySQL 5.0

23.3. MySQL Connector/J

MySQL provides connectivity for client applications developed in the Java programming language via a JDBC driver, which is called MySQL Connector/J.

MySQL Connector/J is a JDBC-3.0 Type 4 driver, which means that is pure Java, implements version 3.0 of the JDBC specification, and communicates directly with the MySQL server using the MySQL protocol.

Although JDBC is useful by itself, we would hope that if you are not familiar with JDBC that after reading the first few sections of this manual, that you would avoid using naked JDBC for all but the most trivial problems and consider using one of the popular persistence frameworks such as Hibernate, Spring's JDBC templates or Ibatis SQL Maps to do the majority of repetitive work and heavier lifting that is sometimes required with JDBC.

This section is not designed to be a complete JDBC tutorial. If you need more information about using JDBC you might be interested in the following online tutorials that are more in-depth than the information presented here:

23.3.1. Connector/J Versions

There are currently three version of MySQL Connector/J available:

  • Connector/J 3.0 provides core functionality and was designed with connectivity to MySQL 3.x or MySQL 4.1 servers, although it will provide basic compatibility with later versions of MySQL. Connector/J 3.0 does not support server-side prepared statements, and does not support any of the features in versions of MySQL later than 4.1.

  • Connector/J 3.1 was designed for connectivity to MySQL 4.1 and MySQL 5.0 servers and provides support for all the functionality in MySQL 5.0 except distributed transaction (XA) support.

  • Connector/J 5.0 provides support for all the functionality offered by Connector/J 3.1 and includes distributed transaction (XA) support.

The current recommended version for Connector/J is 5.0. This guide covers all three connector versions, with specific notes given where a setting applies to a specific option.

23.3.1.1. Java Versions Supported

MySQL Connector/J supports Java-2 JVMs, including:

  • JDK 1.2.x

  • JDK 1.3.x

  • JDK 1.4.x

  • JDK 1.5.x

If you are building Connector/J from source using the source distribution (see Section 23.3.2.4, “Installing from the Development Source Tree”) then you must use JDK 1.4.x or newer to compiler the Connector package.

MySQL Connector/J does not support JDK-1.1.x or JDK-1.0.x

Because of the implementation of , Connector/J 3.1.0 and newer will not run on JDKs older than 1.4 unless the class verifier is turned off (by setting the option to the Java runtime). This is because the class verifier will try to load the class definition for even though it is not accessed by the driver unless you actually use savepoint functionality.

Caching functionality provided by Connector/J 3.1.0 or newer is also not available on JVMs older than 1.4.x, as it relies on which was first available in JDK-1.4.0.

23.3.2. Installing Connector/J

You can install the Connector/J package using two methods, using either the binary or source distribution. The binary distribution provides the easiest methods for installation; the source distribution enables you to customize your installation further. With with either solution, you must

23.3.2.1. Installing Connector/J from a Binary Distribution

The easiest method of installation is to use the binary distribution of the Connector/J package. The binary distribution is available either as a Tar/Gzip or Zip file which you must extract to a suitable location and then optionally make the information about the package available by changing your (see Section 23.3.2.2, “Installing the Driver and Configuring the ).

MySQL Connector/J is distributed as a .zip or .tar.gz archive containing the sources, the class files, and the JAR archive named -bin.jar, and starting with Connector/J 3.1.8 a debug build of the driver in a file named -bin-g.jar.

Starting with Connector/J 3.1.9, the files that constitute the JAR files are only included as part of the driver JAR file.

You should not use the debug build of the driver unless instructed to do so when reporting a problem ors bug to MySQL AB, as it is not designed to be run in production environments, and will have adverse performance impact when used. The debug binary also depends on the Aspect/J runtime library, which is located in the file that comes with the Connector/J distribution.

You will need to use the appropriate graphical or command-line utility to un-archive the distribution (for example, WinZip for the .zip archive, and tar for the .tar.gz archive). Because there are potentially long filenames in the distribution, we use the GNU tar archive format. You will need to use GNU tar (or an application that understands the GNU tar archive format) to unpack the .tar.gz variant of the distribution.

23.3.2.2. Installing the Driver and Configuring the

Once you have extracted the distribution archive, you can install the driver by placing in your classpath, either by adding the full path to it to your environment variable, or by directly specifying it with the command line switch -cp when starting your JVM.

If you are going to use the driver with the JDBC DriverManager, you would use as the class that implements java.sql.Driver.

You can set the environment variableunder UNIX, Linux or Mac OS X either locally for a user within their , or other login file. You can also set it globally by editing the global file.

For example, under a C shell (csh, tcsh) you would add the Connector/J driver to your using the following:

shell> setenv CLASSPATH /path/to/mysql-connector-java-[version]-bin.jar:$CLASSPATH

Or with a Bourne-compatible shell (sh, ksh, bash):

export set CLASSPATH=/path/to/mysql-connector-java-[version]-bin.jar:$CLASSPATH

Within Windows 2000, Windows XP and Windows Server 2003, you must set the environment variable through the System control panel.

If you want to use MySQL Connector/J with an application server such as Tomcat or JBoss, you will have to read your vendor's documentation for more information on how to configure third-party class libraries, as most application servers ignore the environment variable. For configuration examples for some J2EE application servers, see Section 23.3.5.2, “Using Connector/J with J2EE and Other Java Frameworks”. However, the authoritative source for JDBC connection pool configuration information for your particular application server is the documentation for that application server.

If you are developing servlets or JSPs, and your application server is J2EE-compliant, you can put the driver's .jar file in the WEB-INF/lib subdirectory of your webapp, as this is a standard location for third party class libraries in J2EE web applications.

You can also use the MysqlDataSource or MysqlConnectionPoolDataSource classes in the package, if your J2EE application server supports or requires them. Starting with Connector/J 5.0.0, the interface is implemented via the class, which supports XA distributed transactions when used in combination with MySQL server version 5.0.

The various MysqlDataSource classes support the following parameters (through standard set mutators):

  • user

  • password

  • serverName (see the previous section about fail-over hosts)

  • databaseName

  • port

23.3.2.3. Upgrading from an Older Version

MySQL AB tries to keep the upgrade process as easy as possible, however as is the case with any software, sometimes changes need to be made in new versions to support new features, improve existing functionality, or comply with new standards.

This section has information about what users who are upgrading from one version of Connector/J to another (or to a new version of the MySQL server, with respect to JDBC functionality) should be aware of.

23.3.2.3.1. Upgrading from MySQL Connector/J 3.0 to 3.1

Connector/J 3.1 is designed to be backward-compatible with Connector/J 3.0 as much as possible. Major changes are isolated to new functionality exposed in MySQL-4.1 and newer, which includes Unicode character sets, server-side prepared statements, SQLState codes returned in error messages by the server and various performance enhancements that can be enabled or disabled via configuration properties.

  • Unicode Character Sets — See the next section, as well as Chapter 10, Character Set Support, for information on this new feature of MySQL. If you have something misconfigured, it will usually show up as an error with a message similar to .

  • Server-side Prepared Statements — Connector/J 3.1 will automatically detect and use server-side prepared statements when they are available (MySQL server version 4.1.0 and newer).

    Starting with version 3.1.7, the driver scans SQL you are preparing via all variants of to determine if it is a supported type of statement to prepare on the server side, and if it is not supported by the server, it instead prepares it as a client-side emulated prepared statement. You can disable this feature by passing emulateUnsupportedPstmts=false in your JDBC URL.

    If your application encounters issues with server-side prepared statements, you can revert to the older client-side emulated prepared statement code that is still presently used for MySQL servers older than 4.1.0 with the connection property useServerPrepStmts=false

  • Datetimes with all-zero components () — These values can not be represented reliably in Java. Connector/J 3.0.x always converted them to NULL when being read from a ResultSet.

    Connector/J 3.1 throws an exception by default when these values are encountered as this is the most correct behavior according to the JDBC and SQL standards. This behavior can be modified using the zeroDateTimeBehavior configuration property. The allowable values are:

    • (the default), which throws an SQLException with an SQLState of .

    • , which returns instead of the date.

    • , which rounds the date to the nearest closest value which is .

    Starting with Connector/J 3.1.7, can be decoupled from this behavior via noDatetimeStringSync=true (the default value is ) so that you can get retrieve the unaltered all-zero value as a String. It should be noted that this also precludes using any time zone conversions, therefore the driver will not allow you to enable noDatetimeStringSync and useTimezone at the same time.

  • New SQLState Codes — Connector/J 3.1 uses SQL:1999 SQLState codes returned by the MySQL server (if supported), which are different from the legacy X/Open state codes that Connector/J 3.0 uses. If connected to a MySQL server older than MySQL-4.1.0 (the oldest version to return SQLStates as part of the error code), the driver will use a built-in mapping. You can revert to the old mapping by using the configuration property useSqlStateCodes=false.

  • — Calling on a BLOB column will now return the address of the byte[] array that represents it, instead of a String representation of the BLOB. BLOBs have no character set, so they can't be converted to java.lang.Strings without data loss or corruption.

    To store strings in MySQL with LOB behavior, use one of the TEXT types, which the driver will treat as a java.sql.Clob.

  • Debug builds — Starting with Connector/J 3.1.8 a debug build of the driver in a file named -bin-g.jar is shipped alongside the normal binary jar file that is named -bin.jar.

    Starting with Connector/J 3.1.9, we don't ship the .class files unbundled, they are only available in the JAR archives that ship with the driver.

    You should not use the debug build of the driver unless instructed to do so when reporting a problem or bug to MySQL AB, as it is not designed to be run in production environments, and will have adverse performance impact when used. The debug binary also depends on the Aspect/J runtime library, which is located in the file that comes with the Connector/J distribution.

23.3.2.3.2. JDBC-Specific Issues When Upgrading to MySQL Server 4.1 or Newer
  • Using the UTF-8 Character Encoding - Prior to MySQL server version 4.1, the UTF-8 character encoding was not supported by the server, however the JDBC driver could use it, allowing storage of multiple character sets in latin1 tables on the server.

    Starting with MySQL-4.1, this functionality is deprecated. If you have applications that rely on this functionality, and can not upgrade them to use the official Unicode character support in MySQL server version 4.1 or newer, you should add the following property to your connection URL:

  • Server-side Prepared Statements - Connector/J 3.1 will automatically detect and use server-side prepared statements when they are available (MySQL server version 4.1.0 and newer). If your application encounters issues with server-side prepared statements, you can revert to the older client-side emulated prepared statement code that is still presently used for MySQL servers older than 4.1.0 with the following connection property:

23.3.2.4. Installing from the Development Source Tree

Caution.  You should read this section only if you are interested in helping us test our new code. If you just want to get MySQL Connector/J up and running on your system, you should use a standard release distribution.

To install MySQL Connector/J from the development source tree, make sure that you have the following prerequisites:

  • Subversion, to check out the sources from our repository (available from http://subversion.tigris.org/).

  • Apache Ant version 1.6 or newer (available from http://ant.apache.org/).

  • JDK-1.4.2 or later. Although MySQL Connector/J can be installed on older JDKs, to compile it from source you must have at least JDK-1.4.2.

The Subversion source code repository for MySQL Connector/J is located at http://svn.mysql.com/svnpublic/connector-j. In general, you should not check out the entire repository because it contains every branch and tag for MySQL Connector/J and is quite large.

To check out and compile a specific branch of MySQL Connector/J, follow these steps:

  1. At the time of this writing, there are three active branches of Connector/J: , and . Check out the latest code from the branch that you want with the following command (replacing and with appropriate version numbers):

    shell> _/connector-j

    This creates a subdirectory in the current directory that contains the latest sources for the requested branch.

  2. Change location to the directory to make it your current working directory:

    shell> 
  3. Issue the following command to compile the driver and create a file suitable for installation:

    shell> 

    This creates a directory in the current directory, where all build output will go. A directory is created in the directory that includes the version number of the sources you are building from. This directory contains the sources, compiled files, and a file suitable for deployment. For other possible targets, including ones that will create a fully packaged distribution, issue the following command:

    shell> 
  4. A newly created file containing the JDBC driver will be placed in the directory .

    Install the newly created JDBC driver as you would a binary file that you download from MySQL by following the instructions in Section 23.3.2.2, “Installing the Driver and Configuring the .

23.3.4. Connector/J (JDBC) Reference

This section of the manual contains reference material for MySQL Connector/J, some of which is automatically generated during the Connector/J build process.

23.3.4.1. Driver/Datasource Class Names, URL Syntax and Configuration Properties for Connector/J

The name of the class that implements java.sql.Driver in MySQL Connector/J is . The class name is also usable to remain backward-compatible with MM.MySQL. You should use this class name when registering the driver, or when otherwise configuring software to use MySQL Connector/J.

The JDBC URL format for MySQL Connector/J is as follows, with items in square brackets ([, ]) being optional:

jdbc:mysql://[host][,failoverhost...][:port]/[database] »
[?propertyName1][=propertyValue1][&propertyName2][=propertyValue2]...

If the hostname is not specified, it defaults to 127.0.0.1. If the port is not specified, it defaults to 3306, the default port number for MySQL servers.

jdbc:mysql://[host:port],[host:port].../[database] »
[?propertyName1][=propertyValue1][&propertyName2][=propertyValue2]...

If the database is not specified, the connection will be made with no default database. In this case, you will need to either call the method on the Connection instance or fully-specify table names using the database name (i.e. ) in your SQL. Not specifying the database to use upon connection is generally only useful when building tools that work with multiple databases, such as GUI database managers.

MySQL Connector/J has fail-over support. This allows the driver to fail-over to any number of slave hosts and still perform read-only queries. Fail-over only happens when the connection is in an state, because fail-over can not happen reliably when a transaction is in progress. Most application servers and connection pools set to at the end of every transaction/connection use.

The fail-over functionality has the following behavior:

  • If the URL property autoReconnect is false: Failover only happens at connection initialization, and failback occurs when the driver determines that the first host has become available again.

  • If the URL property autoReconnect is true: Failover happens when the driver determines that the connection has failed (before every query), and falls back to the first host when it determines that the host has become available again (after queries have been issued).

In either case, whenever you are connected to a "failed-over" server, the connection will be set to read-only state, so queries that would modify data will have exceptions thrown (the query will never be processed by the MySQL server).

Configuration properties define how Connector/J will make a connection to a MySQL server. Unless otherwise noted, properties can be set for a DataSource object or for a Connection object.

Configuration Properties can be set in one of the following ways:

  • Using the set*() methods on MySQL implementations of java.sql.DataSource (which is the preferred method when using implementations of java.sql.DataSource):

    • com.mysql.jdbc.jdbc2.optional.MysqlDataSource

    • com.mysql.jdbc.jdbc2.optional.MysqlConnectionPoolDataSource

  • As a key/value pair in the java.util.Properties instance passed to or

  • As a JDBC URL parameter in the URL given to , or the MySQL implementations of the method.

    Note.  If the mechanism you use to configure a JDBC URL is XML-based, you will need to use the XML character literal & to separate configuration parameters, as the ampersand is a reserved character for XML.

The properties are listed in the following tables.

Connection/Authentication. 

Property Name Definition Default Value Since Version
user The user to connect as   all
password The password to use when connecting   all
socketFactory The name of the class that the driver should use for creating socket connections to the server. This class must implement the interface and have public no-args constructor. com.mysql.jdbc.StandardSocketFactory 3.0.3
connectTimeout Timeout for socket connect (in milliseconds), with 0 being no timeout. Only works on JDK-1.4 or newer. Defaults to 0. 0 3.0.1
socketTimeout Timeout on network socket operations (0, the default means no timeout). 0 3.0.1
useConfigs Load the comma-delimited list of configuration properties before parsing the URL or applying user-specified properties. See Section 23.3.4.1, “Driver/Datasource Class Names, URL Syntax and Configuration Properties for Connector/J”   3.1.5
interactiveClient Set the CLIENT_INTERACTIVE flag, which tells MySQL to timeout connections based on INTERACTIVE_TIMEOUT instead of WAIT_TIMEOUT false 3.1.0
propertiesTransform An implementation of that the driver will use to modify URL properties passed to the driver before attempting a connection   3.1.4
useCompression Use zlib compression when communicating with the server (true/false)? Defaults to . false 3.0.17

High Availability and Clustering. 

Property Name Definition Default Value Since Version
autoReconnect Should the driver try to re-establish stale and/or dead connections? If enabled the driver will throw an exception for a queries issued on a stale or dead connection, which belong to the current transaction, but will attempt reconnect before the next query issued on the connection in a new transaction. The use of this feature is not recommended, because it has side effects related to session state and data consistency when applications don'thandle SQLExceptions properly, and is only designed to be used when you are unable to configure your application to handle SQLExceptions resulting from dead andstale connections properly. Alternatively, investigate setting the MySQL server variable "wait_timeout"to some high value rather than the default of 8 hours. false 1.1
autoReconnectForPools Use a reconnection strategy appropriate for connection pools (defaults to 'false') false 3.1.3
failOverReadOnly When failing over in autoReconnect mode, should the connection be set to 'read-only'? true 3.0.12
reconnectAtTxEnd If autoReconnect is set to true, should the driver attempt reconnectionsat the end of every transaction? false 3.0.10
roundRobinLoadBalance When autoReconnect is enabled, and failoverReadonly is false, should we pick hosts to connect to on a round-robin basis? false 3.1.2
queriesBeforeRetryMaster Number of queries to issue before falling back to master when failed over (when using multi-host failover). Whichever condition is met first, 'queriesBeforeRetryMaster' or 'secondsBeforeRetryMaster' will cause an attempt to be made to reconnect to the master. Defaults to 50. 50 3.0.2
secondsBeforeRetryMaster How long should the driver wait, when failed over, before attempting to reconnect to the master server? Whichever condition is met first, 'queriesBeforeRetryMaster' or 'secondsBeforeRetryMaster' will cause an attempt to be made to reconnect to the master. Time in seconds, defaults to 30 30 3.0.2
resourceId A globally unique name that identifies the resource that this datasource or connection is connected to, used for when the driver can't determine this value based on hostnames used in the URL   5.0.1

Security. 

Property Name Definition Default Value Since Version
allowMultiQueries Allow the use of ';' to delimit multiple queries during one statement (true/false, defaults to 'false' false 3.1.1
useSSL Use SSL when communicating with the server (true/false), defaults to 'false' false 3.0.2
requireSSL Require SSL connection if useSSL=true? (defaults to 'false'). false 3.1.0
allowUrlInLocalInfile Should the driver allow URLs in 'LOAD DATA LOCAL INFILE' statements? false 3.1.4
paranoid Take measures to prevent exposure sensitive information in error messages and clear data structures holding sensitive data when possible? (defaults to 'false') false 3.0.1

Performance Extensions. 

Property Name Definition Default Value Since Version
metadataCacheSize The number of queries to cacheResultSetMetadata for if cacheResultSetMetaData is set to 'true' (default 50) 50 3.1.1
prepStmtCacheSize If prepared statement caching is enabled, how many prepared statements should be cached? 25 3.0.10
prepStmtCacheSqlLimit If prepared statement caching is enabled, what's the largest SQL the driver will cache the parsing for? 256 3.0.10
useCursorFetch If connected to MySQL > 5.0.2, and > 0 on a statement, should that statement use cursor-based fetching to retrieve rows? false 5.0.0
blobSendChunkSize Chunk to use when sending BLOB/CLOBs via ServerPreparedStatements 1048576 3.1.9
cacheCallableStmts Should the driver cache the parsing stage of CallableStatements false 3.1.2
cachePrepStmts Should the driver cache the parsing stage of PreparedStatements of client-side prepared statements, the check for suitability of server-side prepared and server-side prepared statements themselves? false 3.0.10
cacheResultSetMetadata Should the driver cache ResultSetMetaData for Statements and PreparedStatements? (Req. JDK-1.4+, true/false, default 'false') false 3.1.1
cacheServerConfiguration Should the driver cache the results of and on a per-URL basis? false 3.1.5
defaultFetchSize The driver will call setFetchSize(n) with this value on all newly-created Statements 0 3.1.9
dontTrackOpenResources The JDBC specification requires the driver to automatically track and close resources, however if your application doesn't do a good job of explicitly calling on statements or result sets, this can cause memory leakage. Setting this property to true relaxes this constraint, and can be more memory efficient for some applications. false 3.1.7
dynamicCalendars Should the driver retrieve the default calendar when required, or cache it per connection/session? false 3.1.5
elideSetAutoCommits If using MySQL-4.1 or newer, should the driver only issue 'set autocommit=n' queries when the server's state doesn't match the requested state by ? false 3.1.3
holdResultsOpenOverStatementClose Should the driver close result sets on as required by the JDBC specification? false 3.1.7
locatorFetchBufferSize If 'emulateLocators' is configured to 'true', what size buffer should be used when fetching BLOB data for getBinaryInputStream? 1048576 3.2.1
rewriteBatchedStatements Should the driver use multiqueries (irregardless of the setting of ) as well as rewriting of prepared statements for into multi-value inserts when executeBatch() is called? Notice that this has the potential for SQL injection if using plain java.sql.Statements and your code doesn't sanitize input correctly. Notice that for prepared statements, server-side prepared statements can not currently take advantage of this rewrite option, and that if you don't specify stream lengths when using PreparedStatement.set*Stream(),the driver won't be able to determine the optimium number of parameters per batch and you might receive anan error from the driver that the resultant packet is too large. Statement.getGeneratedKeys() for these rewritten statements only works when the entire batch includes INSERT statements. false 3.1.13
useFastIntParsing Use internal String->Integer conversion routines to avoid excessive object creation? true 3.1.4
useJvmCharsetConverters Always use the character encoding routines built into the JVM, rather than using lookup tables for single-byte character sets? (The default of "true" for this is appropriate for newer JVMs true 5.0.1
useLocalSessionState Should the driver refer to the internal values of autocommit and transaction isolation that are set by Connection.setAutoCommit() and Connection.setTransactionIsolation(), rather than querying the database? false 3.1.7
useReadAheadInput Use newer, optimized non-blocking, buffered input stream when reading from the server? true 3.1.5

Debuging/Profiling. 

Property Name Definition Default Value Since Version
logger The name of a class that implements 'com.mysql.jdbc.log.Log' that will be used to log messages to.(default is 'com.mysql.jdbc.log.StandardLogger', which logs to STDERR) com.mysql.jdbc.log.StandardLogger 3.1.1
profileSQL Trace queries and their execution/fetch times to the configured logger (true/false) defaults to 'false' false 3.1.0
reportMetricsIntervalMillis If 'gatherPerfMetrics' is enabled, how often should they be logged (in ms)? 30000 3.1.2
maxQuerySizeToLog Controls the maximum length/size of a query that will get logged when profiling or tracing 2048 3.1.3
packetDebugBufferSize The maximum number of packets to retain when 'enablePacketDebug' is true 20 3.1.3
slowQueryThresholdMillis If 'logSlowQueries' is enabled, how long should a query (in ms) before it is logged as 'slow'? 2000 3.1.2
useUsageAdvisor Should the driver issue 'usage' warnings advising proper and efficient usage of JDBC and MySQL Connector/J to the log (true/false, defaults to 'false')? false 3.1.1
autoGenerateTestcaseScript Should the driver dump the SQL it is executing, including server-side prepared statements to STDERR? false 3.1.9
dumpMetadataOnColumnNotFound Should the driver dump the field-level metadata of a result set into the exception message when ResultSet.findColumn() fails? false 3.1.13
dumpQueriesOnException Should the driver dump the contents of the query sent to the server in the message for SQLExceptions? false 3.1.3
enablePacketDebug When enabled, a ring-buffer of 'packetDebugBufferSize' packets will be kept, and dumped when exceptions are thrown in key areas in the driver's code false 3.1.3
explainSlowQueries If 'logSlowQueries' is enabled, should the driver automatically issue an 'EXPLAIN' on the server and send the results to the configured log at a WARN level? false 3.1.2
logSlowQueries Should queries that take longer than 'slowQueryThresholdMillis' be logged? false 3.1.2
traceProtocol Should trace-level network protocol be logged? false 3.1.2

Miscellaneous. 

Property Name Definition Default Value Since Version
useUnicode Should the driver use Unicode character encodings when handling strings? Should only be used when the driver can't determine the character set mapping, or you are trying to 'force' the driver to use a character set that MySQL either doesn't natively support (such as UTF-8), true/false, defaults to 'true' true 1.1g
characterEncoding If 'useUnicode' is set to true, what character encoding should the driver use when dealing with strings? (defaults is to 'autodetect')   1.1g
characterSetResults Character set to tell the server to return results as.   3.0.13
connectionCollation If set, tells the server to use this collation via 'set collation_connection'   3.0.13
sessionVariables A comma-separated list of name/value pairs to be sent as SET SESSION ... to the server when the driver connects.   3.1.8
allowNanAndInf Should the driver allow NaN or +/- INF values in PreparedStatement.setDouble()? false 3.1.5
autoClosePStmtStreams Should the driver automatically call .close() on streams/readers passed as arguments via set*() methods? false 3.1.12
autoDeserialize Should the driver automatically detect and de-serialize objects stored in BLOB fields? false 3.1.5
capitalizeTypeNames Capitalize type names in DatabaseMetaData? (usually only useful when using WebObjects, true/false, defaults to 'false') false 2.0.7
clobCharacterEncoding The character encoding to use for sending and retrieving TEXT, MEDIUMTEXT and LONGTEXT values instead of the configured connection characterEncoding   5.0.0
clobberStreamingResults This will cause a 'streaming' ResultSet to be automatically closed, and any outstanding data still streaming from the server to be discarded if another query is executed before all the data has been read from the server. false 3.0.9
continueBatchOnError Should the driver continue processing batch commands if one statement fails. The JDBC spec allows either way (defaults to 'true'). true 3.0.3
createDatabaseIfNotExist Creates the database given in the URL if it doesn't yet exist. Assumes the configured user has permissions to create databases. false 3.1.9
emptyStringsConvertToZero Should the driver allow conversions from empty string fields to numeric values of '0'? true 3.1.8
emulateLocators N/A false 3.1.0
emulateUnsupportedPstmts Should the driver detect prepared statements that are not supported by the server, and replace them with client-side emulated versions? true 3.1.7
ignoreNonTxTables Ignore non-transactional table warning for rollback? (defaults to 'false'). false 3.0.9
jdbcCompliantTruncation Should the driver throw java.sql.DataTruncation exceptions when data is truncated as is required by the JDBC specification when connected to a server that supports warnings(MySQL 4.1.0 and newer)? true 3.1.2
maxRows The maximum number of rows to return (0, the default means return all rows). -1 all versions
noAccessToProcedureBodies When determining procedure parameter types for CallableStatements, and the connected user can't access procedure bodies through "SHOW CREATE PROCEDURE" or select on mysql.proc should the driver instead create basic metadata (all parameters reported as INOUT VARCHARs) instead of throwing an exception? false 5.0.3
noDatetimeStringSync Don't ensure that ResultSet.getDatetimeType().toString().equals(ResultSet.getString()) false 3.1.7
noTimezoneConversionForTimeType Don't convert TIME values using the server timezone if 'useTimezone'='true' false 5.0.0
nullCatalogMeansCurrent When DatabaseMetadataMethods ask for a 'catalog' parameter, does the value null mean use the current catalog? (this is not JDBC-compliant, but follows legacy behavior from earlier versions of the driver) true 3.1.8
nullNamePatternMatchesAll Should DatabaseMetaData methods that accept *pattern parameters treat null the same as '%' (this is not JDBC-compliant, however older versions of the driver accepted this departure from the specification) true 3.1.8
overrideSupportsIntegrityEnhancementFacility Should the driver return "true" for DatabaseMetaData.supportsIntegrityEnhancementFacility() even if the database doesn't support it to workaround applications that require this method to return "true" to signal support of foreign keys, even though the SQL specification states that this facility contains much more than just foreign key support (one such application being OpenOffice)? false 3.1.12
pedantic Follow the JDBC spec to the letter. false 3.0.0
pinGlobalTxToPhysicalConnection When using XAConnections, should the driver ensure that operations on a given XID are always routed to the same physical connection? This allows the XAConnection to support "XA START ... JOIN" after "XA END" has been called false 5.0.1
processEscapeCodesForPrepStmts Should the driver process escape codes in queries that are prepared? true 3.1.12
relaxAutoCommit If the version of MySQL the driver connects to does not support transactions, still allow calls to commit(), rollback() and setAutoCommit() (true/false, defaults to 'false')? false 2.0.13
retainStatementAfterResultSetClose Should the driver retain the Statement reference in a ResultSet after ResultSet.close() has been called. This is not JDBC-compliant after JDBC-4.0. false 3.1.11
rollbackOnPooledClose Should the driver issue a rollback() when the logical connection in a pool is closed? true 3.0.15
runningCTS13 Enables workarounds for bugs in Sun's JDBC compliance testsuite version 1.3 false 3.1.7
serverTimezone Override detection/mapping of timezone. Used when timezone from server doesn't map to Java timezone   3.0.2
strictFloatingPoint Used only in older versions of compliance test false 3.0.0
strictUpdates Should the driver do strict checking (all primary keys selected) of updatable result sets (true, false, defaults to 'true')? true 3.0.4
tinyInt1isBit Should the driver treat the datatype TINYINT(1) as the BIT type (because the server silently converts BIT -> TINYINT(1) when creating tables)? true 3.0.16
transformedBitIsBoolean If the driver converts TINYINT(1) to a different type, should it use BOOLEAN instead of BIT for future compatibility with MySQL-5.0, as MySQL-5.0 has a BIT type? false 3.1.9
ultraDevHack Create PreparedStatements for prepareCall() when required, because UltraDev is broken and issues a prepareCall() for _all_ statements? (true/false, defaults to 'false') false 2.0.3
useGmtMillisForDatetimes Convert between session timezone and GMT before creating Date and Timestamp instances (value of "false" is legacy behavior, "true" leads to more JDBC-compliant behavior. false 3.1.12
useHostsInPrivileges Add '@hostname' to users in DatabaseMetaData.getColumn/TablePrivileges() (true/false), defaults to 'true'. true 3.0.2
useInformationSchema When connected to MySQL-5.0.7 or newer, should the driver use the INFORMATION_SCHEMA to derive information used by DatabaseMetaData? false 5.0.0
useJDBCCompliantTimezoneShift Should the driver use JDBC-compliant rules when converting TIME/TIMESTAMP/DATETIME values' timezone information for those JDBC arguments which take a java.util.Calendar argument? (Notice that this option is exclusive of the "useTimezone=true" configuration option.) false 5.0.0
useOldUTF8Behavior Use the UTF-8 behavior the driver did when communicating with 4.0 and older servers false 3.1.6
useOnlyServerErrorMessages Don't prepend 'standard' SQLState error messages to error messages returned by the server. true 3.0.15
useServerPrepStmts Use server-side prepared statements if the server supports them? (defaults to 'true'). true 3.1.0
useSqlStateCodes Use SQL Standard state codes instead of 'legacy' X/Open/SQL state codes (true/false), default is 'true' true 3.1.3
useStreamLengthsInPrepStmts Honor stream length parameter in PreparedStatement/ResultSet.setXXXStream() method calls (true/false, defaults to 'true')? true 3.0.2
useTimezone Convert time/date types between client and server timezones (true/false, defaults to 'false')? false 3.0.2
useUnbufferedInput Don't use BufferedInputStream for reading data from the server true 3.0.11
yearIsDateType Should the JDBC driver treat the MySQL type "YEAR" as a java.sql.Date, or as a SHORT? true 3.1.9
zeroDateTimeBehavior What should happen when the driver encounters DATETIME values that are composed entirely of zeroes (used by MySQL to represent invalid dates)? Valid values are 'exception', 'round' and 'convertToNull'. exception 3.1.4

Connector/J also supports access to MySQL via named pipes on Windows NT/2000/XP using the NamedPipeSocketFactory as a plugin-socket factory via the socketFactory property. If you don't use a namedPipePath property, the default of '\\.\pipe\MySQL' will be used. If you use the , the hostname and port number values in the JDBC url will be ignored. You can enable this feature using:

socketFactory=com.mysql.jdbc.NamedPipeSocketFactory
        

Named pipes only work when connecting to a MySQL server on the same physical machine as the one the JDBC driver is being used on. In simple performance tests, it appears that named pipe access is between 30%-50% faster than the standard TCP/IP access.

You can create your own socket factories by following the example code in , or .

23.3.4.2. JDBC API Implementation Notes

MySQL Connector/J passes all of the tests in the publicly-available version of Sun's JDBC compliance test suite. However, in many places the JDBC specification is vague about how certain functionality should be implemented, or the specification allows leeway in implementation.

This section gives details on a interface-by-interface level about how certain implementation decisions may affect how you use MySQL Connector/J.

  • Blob

    The Blob implementation does not allow in-place modification (they are copies, as reported by the method). Because of this, you should use the corresponding or (in the case of updatable result sets) methods to save changes back to the database.

    Starting with Connector/J version 3.1.0, you can emulate Blobs with locators by adding the property 'emulateLocators=true' to your JDBC URL. You must then use a column alias with the value of the column set to the actual name of the Blob column in the that you write to retrieve the Blob. The must also reference only one table, the table must have a primary key, and the must cover all columns that make up the primary key. The driver will then delay loading the actual Blob data until you retrieve the Blob and call retrieval methods (, , and so forth) on it.

  • CallableStatement

    Starting with Connector/J 3.1.1, stored procedures are supported when connecting to MySQL version 5.0 or newer via the interface. Currently, the method of is not supported.

  • Clob

    The Clob implementation does not allow in-place modification (they are copies, as reported by the method). Because of this, you should use the method to save changes back to the database. The JDBC API does not have a method.

  • Connection

    Unlike older versions of MM.MySQL the method does not ping the server to determine if it is alive. In accordance with the JDBC specification, it only returns true if has been called on the connection. If you need to determine if the connection is still valid, you should issue a simple query, such as . The driver will throw an exception if the connection is no longer valid.

  • DatabaseMetaData

    Foreign Key information (/ and ) is only available from InnoDB tables. However, the driver uses to retrieve this information, so when other storage engines support foreign keys, the driver will transparently support them as well.

  • PreparedStatement

    PreparedStatements are implemented by the driver, as MySQL does not have a prepared statement feature. Because of this, the driver does not implement or as it would require the driver to have a complete SQL parser in the client.

    Starting with version 3.1.0 MySQL Connector/J, server-side prepared statements and binary-encoded result sets are used when the server supports them.

    Take care when using a server-side prepared statement with large parameters that are set via , , , , or . If you want to re-execute the statement with any large parameter changed to a non-large parameter, it is necessary to call and set all parameters again. The reason for this is as follows:

    • The driver streams the large data out-of-band to the prepared statement on the server side when the parameter is set (before execution of the prepared statement).

    • Once that has been done, the stream used to read the data on the client side is closed (as per the JDBC spec), and can't be read from again.

    • If a parameter changes from large to non-large, the driver must reset the server-side state of the prepared statement to allow the parameter that is being changed to take the place of the prior large value. This removes all of the large data that has already been sent to the server, thus requiring the data to be re-sent, via the , , , or methods.

    Consequently, if you want to change the type of a parameter to a non-large one, you must call and set all parameters of the prepared statement again before it can be re-executed.

  • ResultSet

    By default, ResultSets are completely retrieved and stored in memory. In most cases this is the most efficient way to operate, and due to the design of the MySQL network protocol is easier to implement. If you are working with ResultSets that have a large number of rows or large values, and can not allocate heap space in your JVM for the memory required, you can tell the driver to stream the results back one row at a time.

    To enable this functionality, you need to create a Statement instance in the following manner:

    stmt = conn.createStatement(java.sql.ResultSet.TYPE_FORWARD_ONLY,
                  java.sql.ResultSet.CONCUR_READ_ONLY);
    stmt.setFetchSize(Integer.MIN_VALUE);

    The combination of a forward-only, read-only result set, with a fetch size of serves as a signal to the driver to stream result sets row-by-row. After this any result sets created with the statement will be retrieved row-by-row.

    There are some caveats with this approach. You will have to read all of the rows in the result set (or close it) before you can issue any other queries on the connection, or an exception will be thrown.

    The earliest the locks these statements hold can be released (whether they be table-level locks or row-level locks in some other storage engine such as ) is when the statement completes.

    If the statement is within scope of a transaction, then locks are released when the transaction completes (which implies that the statement needs to complete first). As with most other databases, statements are not complete until all the results pending on the statement are read or the active result set for the statement is closed.

    Therefore, if using streaming results, you should process them as quickly as possible if you want to maintain concurrent access to the tables referenced by the statement producing the result set.

  • ResultSetMetaData

    The method only works when using MySQL servers 4.0 and newer.

  • Statement

    When using versions of the JDBC driver earlier than 3.2.1, and connected to server versions earlier than 5.0.3, the "setFetchSize()" method has no effect, other than to toggle result set streaming as described above.

    MySQL does not support SQL cursors, and the JDBC driver doesn't emulate them, so "setCursorName()" has no effect.

23.3.4.3. Java, JDBC and MySQL Types

MySQL Connector/J is flexible in the way it handles conversions between MySQL data types and Java data types.

In general, any MySQL data type can be converted to a java.lang.String, and any numerical type can be converted to any of the Java numerical types, although round-off, overflow, or loss of precision may occur.

Starting with Connector/J 3.1.0, the JDBC driver will issue warnings or throw DataTruncation exceptions as is required by the JDBC specification unless the connection was configured not to do so by using the property jdbcCompliantTruncation and setting it to .

The conversions that are always guaranteed to work are listed in the following table:

Connection Properties - Miscellaneous. 

These MySQL Data Types Can always be converted to these Java types

Note: round-off, overflow or loss of precision may occur if you choose a Java numeric data type that has less precision or capacity than the MySQL data type you are converting to/from.

The method uses the following type conversions between MySQL and Java types, following the JDBC specification where appropriate:

MySQL Types to Java Types for ResultSet.getObject(). 

MySQL Type Name Returned as Java Class
BIT(1) (new in MySQL-5.0)
BIT( > 1) (new in MySQL-5.0)
TINYINT if the configuration property is set to (the default) and the storage size is 1, or if not.
BOOL, BOOLEAN See TINYINT, above as these are aliases for TINYINT(1), currently.
SMALLINT[(M)] [UNSIGNED] (regardless if UNSIGNED or not)
MEDIUMINT[(M)] [UNSIGNED] if UNSIGNED
INT,INTEGER[(M)] [UNSIGNED] , if UNSIGNED
BIGINT[(M)] [UNSIGNED] , if UNSIGNED
FLOAT[(M,D)]
DOUBLE[(M,B)]
DECIMAL[(M[,D])]
DATE
DATETIME
TIMESTAMP[(M)]
TIME
YEAR[(2|4)] (with the date set two January 1st, at midnight)
CHAR(M) (unless the character set for the column is BINARY, then is returned.
VARCHAR(M) [BINARY] (unless the character set for the column is BINARY, then is returned.
BINARY(M)
VARBINARY(M)
TINYBLOB
TINYTEXT
BLOB
TEXT
MEDIUMBLOB
MEDIUMTEXT
LONGBLOB
LONGTEXT
ENUM('value1','value2',...)
SET('value1','value2',...)

23.3.4.4. Using Character Sets and Unicode

All strings sent from the JDBC driver to the server are converted automatically from native Java Unicode form to the client character encoding, including all queries sent via , , as well as all and parameters with the exclusion of parameters set using , , , and .

Prior to MySQL Server 4.1, Connector/J supported a single character encoding per connection, which could either be automatically detected from the server configuration, or could be configured by the user through the and "" properties.

Starting with MySQL Server 4.1, Connector/J supports a single character encoding between client and server, and any number of character encodings for data returned by the server to the client in .

The character encoding between client and server is automatically detected upon connection. The encoding used by the driver is specified on the server via the system variable for server versions older than 4.1.0 and for server versions 4.1.0 and newer. For more information, see Section 10.3.1, “Server Character Set and Collation”.

To override the automatically-detected encoding on the client side, use the property in the URL used to connect to the server.

When specifying character encodings on the client side, Java-style names should be used. The following table lists Java-style names for MySQL character sets:

MySQL to Java Encoding Name Translations. 

MySQL Character Set Name Java-Style Character Encoding Name
usa7 US-ASCII
big5 Big5
gbk GBK
sjis SJIS (or Cp932 or MS932 for MySQL Server < 4.1.11)
cp932 Cp932 or MS932 (MySQL Server > 4.1.11)
gb2312 EUC_CN
ujis EUC_JP
euc_kr EUC_KR
latin1 ISO8859_1
latin1_de ISO8859_1
german1 ISO8859_1
danish ISO8859_1
latin2 ISO8859_2
czech ISO8859_2
hungarian ISO8859_2
croat ISO8859_2
greek ISO8859_7
hebrew ISO8859_8
latin5 ISO8859_9
latvian ISO8859_13
latvian1 ISO8859_13
estonia ISO8859_13
dos Cp437
pclatin2 Cp852
cp866 Cp866
koi8_ru KOI8_R
tis620 TIS620
win1250 Cp1250
win1250ch Cp1250
win1251 Cp1251
cp1251 Cp1251
win1251ukr Cp1251
cp1257 Cp1257
macroman MacRoman
macce MacCentralEurope
utf8 UTF-8
ucs2 UnicodeBig

Warning.  Do not issue the query 'set names' with Connector/J, as the driver will not detect that the character set has changed, and will continue to use the character set detected during the initial connection setup.

To allow multiple character sets to be sent from the client, the UTF-8 encoding should be used, either by configuring as the default server character set, or by configuring the JDBC driver to use UTF-8 through the property.

23.3.4.5. Connecting Securely Using SSL

SSL in MySQL Connector/J encrypts all data (other than the initial handshake) between the JDBC driver and the server. The performance penalty for enabling SSL is an increase in query processing time between 35% and 50%, depending on the size of the query, and the amount of data it returns.

For SSL Support to work, you must have the following:

You will first need to import the MySQL server CA Certificate into a Java truststore. A sample MySQL server CA Certificate is located in the subdirectory of the MySQL source distribution. This is what SSL will use to determine if you are communicating with a secure MySQL server.

To use Java's keytool to create a truststore in the current directory , and import the server's CA certificate (), you can do the following (assuming that keytool is in your path. The keytool should be located in the subdirectory of your JDK or JRE):

shell> keytool -import -alias mysqlServerCACert -file cacert.pem -keystore truststore
        

Keytool will respond with the following information:

Enter keystore password:  *********
Owner: [email protected], CN=Walrus, O=MySQL AB, L=Orenburg, ST=Some
-State, C=RU
Issuer: [email protected], CN=Walrus, O=MySQL AB, L=Orenburg, ST=Som
e-State, C=RU
Serial number: 0
Valid from: Fri Aug 02 16:55:53 CDT 2002 until: Sat Aug 02 16:55:53 CDT 2003
Certificate fingerprints:
         MD5:  61:91:A0:F2:03:07:61:7A:81:38:66:DA:19:C4:8D:AB
         SHA1: 25:77:41:05:D5:AD:99:8C:14:8C:CA:68:9C:2F:B8:89:C3:34:4D:6C
Trust this certificate? [no]:  yes
Certificate was added to keystore

You will then need to generate a client certificate, so that the MySQL server knows that it is talking to a secure client:

 shell> keytool -genkey -keyalg rsa -alias mysqlClientCertificate -keystore keystore 

Keytool will prompt you for the following information, and create a keystore named in the current directory.

You should respond with information that is appropriate for your situation:

Enter keystore password:  *********
What is your first and last name?
  [Unknown]:  Matthews
What is the name of your organizational unit?
  [Unknown]:  Software Development
What is the name of your organization?
  [Unknown]:  MySQL AB
What is the name of your City or Locality?
  [Unknown]:  Flossmoor
What is the name of your State or Province?
  [Unknown]:  IL
What is the two-letter country code for this unit?
  [Unknown]:  US
Is <CN=Matthews, OU=Software Development, O=MySQL AB,
 L=Flossmoor, ST=IL, C=US> correct?
  [no]:  y

Enter key password for <mysqlClientCertificate>
        (RETURN if same as keystore password):

Finally, to get JSSE to use the keystore and truststore that you have generated, you need to set the following system properties when you start your JVM, replacing path_to_keystore_file with the full path to the keystore file you created, path_to_truststore_file with the path to the truststore file you created, and using the appropriate password values for each property.

-Djavax.net.ssl.keyStore=path_to_keystore_file
-Djavax.net.ssl.keyStorePassword=*********
-Djavax.net.ssl.trustStore=path_to_truststore_file
-Djavax.net.ssl.trustStorePassword=********* 

You will also need to set useSSL to in your connection parameters for MySQL Connector/J, either by adding to your URL, or by setting the property useSSL to in the instance you pass to .

You can test that SSL is working by turning on JSSE debugging (as detailed below), and look for the following key events:

...
 *** ClientHello, v3.1
 RandomCookie:  GMT: 1018531834 bytes = { 199, 148, 180, 215, 74, 12, 54, 244, 0, 168, 55, 103, 215, 64, 16, 138, 225, 190, 132, 153, 2, 217, 219, 239, 202, 19, 121, 78 }
 Session ID:  {}
 Cipher Suites:  { 0, 5, 0, 4, 0, 9, 0, 10, 0, 18, 0, 19, 0, 3, 0, 17 }
 Compression Methods:  { 0 }
 ***
 [write] MD5 and SHA1 hashes:  len = 59
 0000: 01 00 00 37 03 01 3D B6   90 FA C7 94 B4 D7 4A 0C  ...7..=.......J.
 0010: 36 F4 00 A8 37 67 D7 40   10 8A E1 BE 84 99 02 D9  [email protected]
 0020: DB EF CA 13 79 4E 00 00   10 00 05 00 04 00 09 00  ....yN..........
 0030: 0A 00 12 00 13 00 03 00   11 01 00                 ...........
 main, WRITE:  SSL v3.1 Handshake, length = 59
 main, READ:  SSL v3.1 Handshake, length = 74
 *** ServerHello, v3.1
 RandomCookie:  GMT: 1018577560 bytes = { 116, 50, 4, 103, 25, 100, 58, 202, 79, 185, 178, 100, 215, 66, 254, 21, 83, 187, 190, 42, 170, 3, 132, 110, 82, 148, 160, 92 }
 Session ID:  {163, 227, 84, 53, 81, 127, 252, 254, 178, 179, 68, 63, 182, 158, 30, 11, 150, 79, 170, 76, 255, 92, 15, 226, 24, 17, 177, 219, 158, 177, 187, 143}
 Cipher Suite:  { 0, 5 }
 Compression Method: 0
 ***
 %% Created:  [Session-1, SSL_RSA_WITH_RC4_128_SHA]
 ** SSL_RSA_WITH_RC4_128_SHA
 [read] MD5 and SHA1 hashes:  len = 74
 0000: 02 00 00 46 03 01 3D B6   43 98 74 32 04 67 19 64  ...F..=.C.t2.g.d
 0010: 3A CA 4F B9 B2 64 D7 42   FE 15 53 BB BE 2A AA 03  :.O..d.B..S..*..
 0020: 84 6E 52 94 A0 5C 20 A3   E3 54 35 51 7F FC FE B2  .nR..\ ..T5Q....
 0030: B3 44 3F B6 9E 1E 0B 96   4F AA 4C FF 5C 0F E2 18  .D?.....O.L.\...
 0040: 11 B1 DB 9E B1 BB 8F 00   05 00                    ..........
 main, READ:  SSL v3.1 Handshake, length = 1712
 ...

JSSE provides debugging (to STDOUT) when you set the following system property: This will tell you what keystores and truststores are being used, as well as what is going on during the SSL handshake and certificate exchange. It will be helpful when trying to determine what is not working when trying to get an SSL connection to happen.

23.3.4.6. Using Master/Slave Replication with ReplicationConnection

Starting with Connector/J 3.1.7, we've made available a variant of the driver that will automatically send queries to a read/write master, or a failover or round-robin loadbalanced set of slaves based on the state of .

An application signals that it wants a transaction to be read-only by calling , this replication-aware connection will use one of the slave connections, which are load-balanced per-vm using a round-robin scheme (a given connection is sticky to a slave unless that slave is removed from service). If you have a write transaction, or if you have a read that is time-sensitive (remember, replication in MySQL is asynchronous), set the connection to be not read-only, by calling and the driver will ensure that further calls are sent to the master MySQL server. The driver takes care of propagating the current state of autocommit, isolation level, and catalog between all of the connections that it uses to accomplish this load balancing functionality.

To enable this functionality, use the " " class when configuring your application server's connection pool or when creating an instance of a JDBC driver for your standalone application. Because it accepts the same URL format as the standard MySQL JDBC driver, does not currently work with -based connection creation unless it is the only MySQL JDBC driver registered with the .

Here is a short, simple example of how ReplicationDriver might be used in a standalone application.

import java.sql.Connection;
import java.sql.ResultSet;
import java.util.Properties;

import com.mysql.jdbc.ReplicationDriver;

public class ReplicationDriverDemo {

    public static void main(String[] args) throws Exception {
        ReplicationDriver driver = new ReplicationDriver();

        Properties props = new Properties();

        // We want this for failover on the slaves
        props.put("autoReconnect", "true");

        // We want to load balance between the slaves
        props.put("roundRobinLoadBalance", "true");

        props.put("user", "foo");
        props.put("password", "bar");

        //
        // Looks like a normal MySQL JDBC url, with a comma-separated list
        // of hosts, the first being the 'master', the rest being any number
        // of slaves that the driver will load balance against
        //

        Connection conn =
            driver.connect("jdbc:mysql://master,slave1,slave2,slave3/test",
                props);

        //
        // Perform read/write work on the master
        // by setting the read-only flag to "false"
        //

        conn.setReadOnly(false);
        conn.setAutoCommit(false);
        conn.createStatement().executeUpdate("UPDATE some_table ....");
        conn.commit();

        //
        // Now, do a query from a slave, the driver automatically picks one
        // from the list
        //

        conn.setReadOnly(true);

        ResultSet rs = conn.createStatement().executeQuery("SELECT a,b,c FROM some_other_table");

         .......
    }
}

23.3.5. Connector/J Notes and Tips

23.3.5.1. Basic JDBC Concepts

This section provides some general JDBC background.

23.3.5.1.1. Connecting to MySQL Using the Interface

When you are using JDBC outside of an application server, the class manages the establishment of Connections.

The needs to be told which JDBC drivers it should try to make Connections with. The easiest way to do this is to use on the class that implements the interface. With MySQL Connector/J, the name of this class is . With this method, you could use an external configuration file to supply the driver class name and driver parameters to use when connecting to a database.

The following section of Java code shows how you might register MySQL Connector/J from the method of your application:

import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.SQLException;

// Notice, do not import com.mysql.jdbc.*
// or you will have problems!

public class LoadDriver {
    public static void main(String[] args) {
        try {
            // The newInstance() call is a work around for some
            // broken Java implementations

            Class.forName("com.mysql.jdbc.Driver").newInstance();
        } catch (Exception ex) {
            // handle the error
        }
}

After the driver has been registered with the , you can obtain a instance that is connected to a particular database by calling :

Example 23.1. Obtaining a connection from the

This example shows how you can obtain a instance from the . There are a few different signatures for the method. You should see the API documentation that comes with your JDK for more specific information on how to use them.

import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.SQLException;

    ... try {
            Connection conn = DriverManager.getConnection("jdbc:mysql://localhost/test?user=monty&password=greatsqldb");

            // Do something with the Connection

           ....
        } catch (SQLException ex) {
            // handle any errors
            System.out.println("SQLException: " + ex.getMessage());
            System.out.println("SQLState: " + ex.getSQLState());
            System.out.println("VendorError: " + ex.getErrorCode());
        }

Once a is established, it can be used to create and objects, as well as retrieve metadata about the database. This is explained in the following sections.

23.3.5.1.2. Using Statements to Execute SQL

objects allow you to execute basic SQL queries and retrieve the results through the class which is described later.

To create a instance, you call the method on the object you have retrieved via one of the or methods described earlier.

Once you have a instance, you can execute a query by calling the method with the SQL you want to use.

To update data in the database, use the method. This method returns the number of rows affected by the update statement.

If you don't know ahead of time whether the SQL statement will be a or an /, then you can use the method. This method will return true if the SQL query was a , or false if it was an , , or statement. If the statement was a query, you can retrieve the results by calling the method. If the statement was an , , or statement, you can retrieve the affected rows count by calling on the instance.

Example 23.2. Using java.sql.Statement to execute a query

// assume that conn is an already created JDBC connection
Statement stmt = null;
ResultSet rs = null;

try {
    stmt = conn.createStatement();
    rs = stmt.executeQuery("SELECT foo FROM bar");

    // or alternatively, if you don't know ahead of time that
    // the query will be a SELECT...

    if (stmt.execute("SELECT foo FROM bar")) {
        rs = stmt.getResultSet();
    }

    // Now do something with the ResultSet ....
} finally {
    // it is a good idea to release
    // resources in a finally{} block
    // in reverse-order of their creation
    // if they are no-longer needed

    if (rs != null) {
        try {
            rs.close();
        } catch (SQLException sqlEx) { // ignore }

        rs = null;
    }

    if (stmt != null) {
        try {
            stmt.close();
        } catch (SQLException sqlEx) { // ignore }

        stmt = null;
    }
}
23.3.5.1.3. Using to Execute Stored Procedures

Starting with MySQL server version 5.0 when used with Connector/J 3.1.1 or newer, the interface is fully implemented with the exception of the method.

See Chapter 17, Stored Procedures and Functions, for more information on MySQL stored procedures.

Connector/J exposes stored procedure functionality through JDBC's interface.

Note.  Current versions of MySQL server do not return enough information for the JDBC driver to provide result set metadata for callable statements. This means that when using , may return .

The following example shows a stored procedure that returns the value of incremented by 1, and the string passed in via as a :

Example 23.3. Stored Procedures

CREATE PROCEDURE demoSp(IN inputParam VARCHAR(255), INOUT inOutParam INT)
BEGIN
    DECLARE z INT;
    SET z = inOutParam + 1;
    SET inOutParam = z;

    SELECT inputParam;

    SELECT CONCAT('zyxw', inputParam);
END

To use the procedure with Connector/J, follow these steps:

  1. Prepare the callable statement by using .

    Notice that you have to use JDBC escape syntax, and that the parentheses surrounding the parameter placeholders are not optional:

    Example 23.4. Using

    import java.sql.CallableStatement;
    
    ...
    
        //
        // Prepare a call to the stored procedure 'demoSp'
        // with two parameters
        //
        // Notice the use of JDBC-escape syntax ({call ...})
        //
    
        CallableStatement cStmt = conn.prepareCall("{call demoSp(?, ?)}");
    
    
    
        cStmt.setString(1, "abcdefg");

    Note.  is an expensive method, due to the metadata retrieval that the driver performs to support output parameters. For performance reasons, you should try to minimize unnecessary calls to by reusing instances in your code.

  2. Register the output parameters (if any exist)

    To retrieve the values of output parameters (parameters specified as or when you created the stored procedure), JDBC requires that they be specified before statement execution using the various methods in the interface:

    Example 23.5. Registering output parameters

    import java.sql.Types;
    ...
    //
    // Connector/J supports both named and indexed
    // output parameters. You can register output
    // parameters using either method, as well
    // as retrieve output parameters using either
    // method, regardless of what method was
    // used to register them.
    //
    // The following examples show how to use
    // the various methods of registering
    // output parameters (you should of course
    // use only one registration per parameter).
    //
    
    //
    // Registers the second parameter as output, and
    // uses the type 'INTEGER' for values returned from
    // getObject()
    //
    
    cStmt.registerOutParameter(2, Types.INTEGER);
    
    //
    // Registers the named parameter 'inOutParam', and
    // uses the type 'INTEGER' for values returned from
    // getObject()
    //
    
    cStmt.registerOutParameter("inOutParam", Types.INTEGER);
    ...
    

  3. Set the input parameters (if any exist)

    Input and in/out parameters are set as for objects. However, also supports setting parameters by name:

    Example 23.6. Setting input parameters

    ...
    
        //
        // Set a parameter by index
        //
    
        cStmt.setString(1, "abcdefg");
    
        //
        // Alternatively, set a parameter using
        // the parameter name
        //
    
        cStmt.setString("inputParameter", "abcdefg");
    
        //
        // Set the 'in/out' parameter using an index
        //
    
        cStmt.setInt(2, 1);
    
        //
        // Alternatively, set the 'in/out' parameter
        // by name
        //
    
        cStmt.setInt("inOutParam", 1);
    
    ...

  4. Execute the , and retrieve any result sets or output parameters.

    Although supports calling any of the execute methods (, or ), the most flexible method to call is , as you do not need to know ahead of time if the stored procedure returns result sets:

    Example 23.7. Retrieving results and output parameter values

    ...
    
        boolean hadResults = cStmt.execute();
    
        //
        // Process all returned result sets
        //
    
        while (hadResults) {
            ResultSet rs = cStmt.getResultSet();
    
            // process result set
            ...
    
            hadResults = rs.getMoreResults();
        }
    
        //
        // Retrieve output parameters
        //
        // Connector/J supports both index-based and
        // name-based retrieval
        //
    
        int outputValue = rs.getInt(2); // index-based
    
        outputValue = rs.getInt("inOutParam"); // name-based
    
    ...

23.3.5.1.4. Retrieving Column Values

Before version 3.0 of the JDBC API, there was no standard way of retrieving key values from databases that supported auto increment or identity columns. With older JDBC drivers for MySQL, you could always use a MySQL-specific method on the interface, or issue the query after issuing an to a table that had an key. Using the MySQL-specific method call isn't portable, and issuing a to get the key's value requires another round-trip to the database, which isn't as efficient as possible. The following code snippets demonstrate the three different ways to retrieve values. First, we demonstrate the use of the new JDBC-3.0 method which is now the preferred method to use if you need to retrieve keys and have access to JDBC-3.0. The second example shows how you can retrieve the same value using a standard query. The final example shows how updatable result sets can retrieve the value when using the method.

Example 23.8. Retrieving column values using

   Statement stmt = null;
   ResultSet rs = null;

   try {

    //
    // Create a Statement instance that we can use for
    // 'normal' result sets assuming you have a
    // Connection 'conn' to a MySQL database already
    // available

    stmt = conn.createStatement(java.sql.ResultSet.TYPE_FORWARD_ONLY,
                                java.sql.ResultSet.CONCUR_UPDATABLE);

    //
    // Issue the DDL queries for the table for this example
    //

    stmt.executeUpdate("DROP TABLE IF EXISTS autoIncTutorial");
    stmt.executeUpdate(
            "CREATE TABLE autoIncTutorial ("
            + "priKey INT NOT NULL AUTO_INCREMENT, "
            + "dataField VARCHAR(64), PRIMARY KEY (priKey))");

    //
    // Insert one row that will generate an AUTO INCREMENT
    // key in the 'priKey' field
    //

    stmt.executeUpdate(
            "INSERT INTO autoIncTutorial (dataField) "
            + "values ('Can I Get the Auto Increment Field?')",
            Statement.RETURN_GENERATED_KEYS);

    //
    // Example of using Statement.getGeneratedKeys()
    // to retrieve the value of an auto-increment
    // value
    //

    int autoIncKeyFromApi = -1;

    rs = stmt.getGeneratedKeys();

    if (rs.next()) {
        autoIncKeyFromApi = rs.getInt(1);
    } else {

        // throw an exception from here
    }

    rs.close();

    rs = null;

    System.out.println("Key returned from getGeneratedKeys():"
        + autoIncKeyFromApi);
} finally {

    if (rs != null) {
        try {
            rs.close();
        } catch (SQLException ex) {
            // ignore
        }
    }

    if (stmt != null) {
        try {
            stmt.close();
        } catch (SQLException ex) {
            // ignore
        }
    }
}

Example 23.9. Retrieving column values using

   Statement stmt = null;
   ResultSet rs = null;

   try {

    //
    // Create a Statement instance that we can use for
    // 'normal' result sets.

    stmt = conn.createStatement();

    //
    // Issue the DDL queries for the table for this example
    //

    stmt.executeUpdate("DROP TABLE IF EXISTS autoIncTutorial");
    stmt.executeUpdate(
            "CREATE TABLE autoIncTutorial ("
            + "priKey INT NOT NULL AUTO_INCREMENT, "
            + "dataField VARCHAR(64), PRIMARY KEY (priKey))");

    //
    // Insert one row that will generate an AUTO INCREMENT
    // key in the 'priKey' field
    //

    stmt.executeUpdate(
            "INSERT INTO autoIncTutorial (dataField) "
            + "values ('Can I Get the Auto Increment Field?')");

    //
    // Use the MySQL LAST_INSERT_ID()
    // function to do the same thing as getGeneratedKeys()
    //

    int autoIncKeyFromFunc = -1;
    rs = stmt.executeQuery("SELECT LAST_INSERT_ID()");

    if (rs.next()) {
        autoIncKeyFromFunc = rs.getInt(1);
    } else {
        // throw an exception from here
    }

    rs.close();

    System.out.println("Key returned from " + "'SELECT LAST_INSERT_ID()': "
        + autoIncKeyFromFunc);

} finally {

    if (rs != null) {
        try {
            rs.close();
        } catch (SQLException ex) {
            // ignore
        }
    }

    if (stmt != null) {
        try {
            stmt.close();
        } catch (SQLException ex) {
            // ignore
        }
    }
}
   

Example 23.10. Retrieving column values in

   Statement stmt = null;
   ResultSet rs = null;

   try {

    //
    // Create a Statement instance that we can use for
    // 'normal' result sets as well as an 'updatable'
    // one, assuming you have a Connection 'conn' to
    // a MySQL database already available
    //

    stmt = conn.createStatement(java.sql.ResultSet.TYPE_FORWARD_ONLY,
                                java.sql.ResultSet.CONCUR_UPDATABLE);

    //
    // Issue the DDL queries for the table for this example
    //

    stmt.executeUpdate("DROP TABLE IF EXISTS autoIncTutorial");
    stmt.executeUpdate(
            "CREATE TABLE autoIncTutorial ("
            + "priKey INT NOT NULL AUTO_INCREMENT, "
            + "dataField VARCHAR(64), PRIMARY KEY (priKey))");

    //
    // Example of retrieving an AUTO INCREMENT key
    // from an updatable result set
    //

    rs = stmt.executeQuery("SELECT priKey, dataField "
       + "FROM autoIncTutorial");

    rs.moveToInsertRow();

    rs.updateString("dataField", "AUTO INCREMENT here?");
    rs.insertRow();

    //
    // the driver adds rows at the end
    //

    rs.last();

    //
    // We should now be on the row we just inserted
    //

    int autoIncKeyFromRS = rs.getInt("priKey");

    rs.close();

    rs = null;

    System.out.println("Key returned for inserted row: "
        + autoIncKeyFromRS);

} finally {

    if (rs != null) {
        try {
            rs.close();
        } catch (SQLException ex) {
            // ignore
        }
    }

    if (stmt != null) {
        try {
            stmt.close();
        } catch (SQLException ex) {
            // ignore
        }
    }
}


   

When you run the preceding example code, you should get the following output: Key returned from : 1 Key returned from : 1 Key returned for inserted row: 2 You should be aware, that at times, it can be tricky to use the query, as that function's value is scoped to a connection. So, if some other query happens on the same connection, the value will be overwritten. On the other hand, the method is scoped by the instance, so it can be used even if other queries happen on the same connection, but not on the same instance.

23.3.5.2. Using Connector/J with J2EE and Other Java Frameworks

This section describes how to use Connector/J in several contexts.

23.3.5.2.1. General J2EE Concepts

This section provides general background on J2EE concepts that pertain to use of Connector/J.

23.3.5.2.1.1. Understanding Connection Pooling

Connection pooling is a technique of creating and managing a pool of connections that are ready for use by any thread that needs them.

This technique of pooling connections is based on the fact that most applications only need a thread to have access to a JDBC connection when they are actively processing a transaction, which usually take only milliseconds to complete. When not processing a transaction, the connection would otherwise sit idle. Instead, connection pooling allows the idle connection to be used by some other thread to do useful work.

In practice, when a thread needs to do work against a MySQL or other database with JDBC, it requests a connection from the pool. When the thread is finished using the connection, it returns it to the pool, so that it may be used by any other threads that want to use it.

When the connection is loaned out from the pool, it is used exclusively by the thread that requested it. From a programming point of view, it is the same as if your thread called every time it needed a JDBC connection, however with connection pooling, your thread may end up using either a new, or already-existing connection.

Connection pooling can greatly increase the performance of your Java application, while reducing overall resource usage. The main benefits to connection pooling are:

  • Reduced connection creation time

    Although this is not usually an issue with the quick connection setup that MySQL offers compared to other databases, creating new JDBC connections still incurs networking and JDBC driver overhead that will be avoided if connections are recycled.

  • Simplified programming model

    When using connection pooling, each individual thread can act as though it has created its own JDBC connection, allowing you to use straight-forward JDBC programming techniques.

  • Controlled resource usage

    If you don't use connection pooling, and instead create a new connection every time a thread needs one, your application's resource usage can be quite wasteful and lead to unpredictable behavior under load.

Remember that each connection to MySQL has overhead (memory, CPU, context switches, and so forth) on both the client and server side. Every connection limits how many resources there are available to your application as well as the MySQL server. Many of these resources will be used whether or not the connection is actually doing any useful work!

Connection pools can be tuned to maximize performance, while keeping resource utilization below the point where your application will start to fail rather than just run slower.

Luckily, Sun has standardized the concept of connection pooling in JDBC through the JDBC-2.0 Optional interfaces, and all major application servers have implementations of these APIs that work fine with MySQL Connector/J.

Generally, you configure a connection pool in your application server configuration files, and access it via the Java Naming and Directory Interface (JNDI). The following code shows how you might use a connection pool from an application deployed in a J2EE application server:

Example 23.11. Using a connection pool with a J2EE application server

import java.sql.Connection;
import java.sql.SQLException;
import java.sql.Statement;

import javax.naming.InitialContext;
import javax.sql.DataSource;


public class MyServletJspOrEjb {

    public void doSomething() throws Exception {
        /*
         * Create a JNDI Initial context to be able to
         *  lookup  the DataSource
         *
         * In production-level code, this should be cached as
         * an instance or static variable, as it can
         * be quite expensive to create a JNDI context.
         *
         * Note: This code only works when you are using servlets
         * or EJBs in a J2EE application server. If you are
         * using connection pooling in standalone Java code, you
         * will have to create/configure datasources using whatever
         * mechanisms your particular connection pooling library
         * provides.
         */

        InitialContext ctx = new InitialContext();

         /*
          * Lookup the DataSource, which will be backed by a pool
          * that the application server provides. DataSource instances
          * are also a good candidate for caching as an instance
          * variable, as JNDI lookups can be expensive as well.
          */

        DataSource ds = (DataSource)ctx.lookup("java:comp/env/jdbc/MySQLDB");

        /*
         * The following code is what would actually be in your
         * Servlet, JSP or EJB 'service' method...where you need
         * to work with a JDBC connection.
         */

        Connection conn = null;
        Statement stmt = null;

        try {
            conn = ds.getConnection();

            /*
             * Now, use normal JDBC programming to work with
             * MySQL, making sure to close each resource when you're
             * finished with it, which allows the connection pool
             * resources to be recovered as quickly as possible
             */

            stmt = conn.createStatement();
            stmt.execute("SOME SQL QUERY");

            stmt.close();
            stmt = null;

            conn.close();
            conn = null;
        } finally {
            /*
             * close any jdbc instances here that weren't
             * explicitly closed during normal code path, so
             * that we don't 'leak' resources...
             */

            if (stmt != null) {
                try {
                    stmt.close();
                } catch (sqlexception sqlex) {
                    // ignore -- as we can't do anything about it here
                }

                stmt = null;
            }

            if (conn != null) {
                try {
                    conn.close();
                } catch (sqlexception sqlex) {
                    // ignore -- as we can't do anything about it here
                }

                conn = null;
            }
        }
    }
}

As shown in the example above, after obtaining the JNDI InitialContext, and looking up the DataSource, the rest of the code should look familiar to anyone who has done JDBC programming in the past.

The most important thing to remember when using connection pooling is to make sure that no matter what happens in your code (exceptions, flow-of-control, and so forth), connections, and anything created by them (such as statements or result sets) are closed, so that they may be re-used, otherwise they will be stranded, which in the best case means that the MySQL server resources they represent (such as buffers, locks, or sockets) may be tied up for some time, or worst case, may be tied up forever.

What's the Best Size for my Connection Pool?

As with all other configuration rules-of-thumb, the answer is: it depends. Although the optimal size depends on anticipated load and average database transaction time, the optimum connection pool size is smaller than you might expect. If you take Sun's Java Petstore blueprint application for example, a connection pool of 15-20 connections can serve a relatively moderate load (600 concurrent users) using MySQL and Tomcat with response times that are acceptable.

To correctly size a connection pool for your application, you should create load test scripts with tools such as Apache JMeter or The Grinder, and load test your application.

An easy way to determine a starting point is to configure your connection pool's maximum number of connections to be unbounded, run a load test, and measure the largest amount of concurrently used connections. You can then work backward from there to determine what values of minimum and maximum pooled connections give the best performance for your particular application.

23.3.5.2.2. Using Connector/J with Tomcat

The following instructions are based on the instructions for Tomcat-5.x, available at http://jakarta.apache.org/tomcat/tomcat-5.0-doc/jndi-datasource-examples-howto.html which is current at the time this document was written.

First, install the .jar file that comes with Connector/J in so that it is available to all applications installed in the container.

Next, Configure the JNDI DataSource by adding a declaration resource to in the context that defines your web application:

<Context ....>

  ...

  <Resource name="jdbc/MySQLDB"
               auth="Container"
               type="javax.sql.DataSource"/>

  <!-- The name you used above, must match _exactly_ here!

       The connection pool will be bound into JNDI with the name
       "java:/comp/env/jdbc/MySQLDB"
  -->

  <ResourceParams name="jdbc/MySQLDB">
    <parameter>
      <name>factory</name>
      <value>org.apache.commons.dbcp.BasicDataSourceFactory</value>
    </parameter>

    <!-- Don't set this any higher than max_connections on your
         MySQL server, usually this should be a 10 or a few 10's
         of connections, not hundreds or thousands -->

    <parameter>
      <name>maxActive</name>
      <value>10</value>
    </parameter>

    <!-- You don't want to many idle connections hanging around
         if you can avoid it, only enough to soak up a spike in
         the load -->

    <parameter>
      <name>maxIdle</name>
      <value>5</value>
    </parameter>

    <!-- Don't use autoReconnect=true, it's going away eventually
         and it's a crutch for older connection pools that couldn't
         test connections. You need to decide whether your application is
         supposed to deal with SQLExceptions (hint, it should), and
         how much of a performance penalty you're willing to pay
         to ensure 'freshness' of the connection -->

    <parameter>
      <name>validationQuery</name>
      <value>SELECT 1</value>
    </parameter>

   <!-- The most conservative approach is to test connections
        before they're given to your application. For most applications
        this is okay, the query used above is very small and takes
        no real server resources to process, other than the time used
        to traverse the network.

        If you have a high-load application you'll need to rely on
        something else. -->

    <parameter>
      <name>testOnBorrow</name>
      <value>true</value>
    </parameter>

   <!-- Otherwise, or in addition to testOnBorrow, you can test
        while connections are sitting idle -->

    <parameter>
      <name>testWhileIdle</name>
      <value>true</value>
    </parameter>

    <!-- You have to set this value, otherwise even though
         you've asked connections to be tested while idle,
         the idle evicter thread will never run -->

    <parameter>
      <name>timeBetweenEvictionRunsMillis</name>
      <value>10000</value>
    </parameter>

    <!-- Don't allow connections to hang out idle too long,
         never longer than what wait_timeout is set to on the
         server...A few minutes or even fraction of a minute
         is sometimes okay here, it depends on your application
         and how much spikey load it will see -->

    <parameter>
      <name>minEvictableIdleTimeMillis</name>
      <value>60000</value>
    </parameter>

    <!-- Username and password used when connecting to MySQL -->

    <parameter>
     <name>username</name>
     <value>someuser</value>
    </parameter>

    <parameter>
     <name>password</name>
     <value>somepass</value>
    </parameter>

    <!-- Class name for the Connector/J driver -->

    <parameter>
       <name>driverClassName</name>
       <value>com.mysql.jdbc.Driver</value>
    </parameter>

    <!-- The JDBC connection url for connecting to MySQL, notice
         that if you want to pass any other MySQL-specific parameters
         you should pass them here in the URL, setting them using the
         parameter tags above will have no effect, you will also
         need to use &amp; to separate parameter values as the
         ampersand is a reserved character in XML -->

    <parameter>
      <name>url</name>
      <value>jdbc:mysql://localhost:3306/test</value>
    </parameter>

  </ResourceParams>
</Context>

In general, you should follow the installation instructions that come with your version of Tomcat, as the way you configure datasources in Tomcat changes from time-to-time, and unfortunately if you use the wrong syntax in your XML file, you will most likely end up with an exception similar to the following:

Error: java.sql.SQLException: Cannot load JDBC driver class 'null ' SQL
state: null 
23.3.5.2.3. Using Connector/J with JBoss

These instructions cover JBoss-4.x. To make the JDBC driver classes available to the application server, copy the .jar file that comes with Connector/J to the directory for your server configuration (which is usually called ). Then, in the same configuration directory, in the subdirectory named deploy, create a datasource configuration file that ends with "-ds.xml", which tells JBoss to deploy this file as a JDBC Datasource. The file should have the following contents:

<datasources>
    <local-tx-datasource>
        <!-- This connection pool will be bound into JNDI with the name
             "java:/MySQLDB" -->

        <jndi-name>MySQLDB</jndi-name>
        <connection-url>jdbc:mysql://localhost:3306/dbname</connection-url>
        <driver-class>com.mysql.jdbc.Driver</driver-class>
        <user-name>user</user-name>
        <password>pass</password>

        <min-pool-size>5</min-pool-size>

        <!-- Don't set this any higher than max_connections on your
         MySQL server, usually this should be a 10 or a few 10's
         of connections, not hundreds or thousands -->

        <max-pool-size>20</max-pool-size>

        <!-- Don't allow connections to hang out idle too long,
         never longer than what wait_timeout is set to on the
         server...A few minutes is usually okay here,
         it depends on your application
         and how much spikey load it will see -->

        <idle-timeout-minutes>5</idle-timeout-minutes>

        <!-- If you're using Connector/J 3.1.8 or newer, you can use
             our implementation of these to increase the robustness
             of the connection pool. -->

        <exception-sorter-class-name>com.mysql.jdbc.integration.jboss.ExtendedMysqlExceptionSorter</exception-sorter-class-name>
        <valid-connection-checker-class-name>com.mysql.jdbc.integration.jboss.MysqlValidConnectionChecker</valid-connection-checker-class-name>

    </local-tx-datasource>
</datasources> 

23.3.5.3. Common Problems and Solutions

There are a few issues that seem to be commonly encountered often by users of MySQL Connector/J. This section deals with their symptoms, and their resolutions.

24.3.5.3.1:

Question:

When I try to connect to the database with MySQL Connector/J, I get the following exception:

SQLException: Server configuration denies access to data source
SQLState: 08001
VendorError: 0

What's going on? I can connect just fine with the MySQL command-line client.

Answer:

MySQL Connector/J must use TCP/IP sockets to connect to MySQL, as Java does not support Unix Domain Sockets. Therefore, when MySQL Connector/J connects to MySQL, the security manager in MySQL server will use its grant tables to determine whether the connection should be allowed.

You must add the necessary security credentials to the MySQL server for this to happen, using the statement to your MySQL Server. See Section 13.5.1.3, “ Syntax”, for more information.

Note.  Testing your connectivity with the mysql command-line client will not work unless you add the flag, and use something other than for the host. The mysql command-line client will use Unix domain sockets if you use the special hostname . If you are testing connectivity to , use as the hostname instead.

Warning.  Changing privileges and permissions improperly in MySQL can potentially cause your server installation to not have optimal security properties.

24.3.5.3.2:

Question:

My application throws an SQLException 'No Suitable Driver'. Why is this happening?

Answer:

There are three possible causes for this error:

  • The Connector/J driver is not in your , see Section 23.3.2, “Installing Connector/J”.

  • The format of your connection URL is incorrect, or you are referencing the wrong JDBC driver.

  • When using DriverManager, the system property has not been populated with the location of the Connector/J driver.

24.3.5.3.3:

Question:

I'm trying to use MySQL Connector/J in an applet or application and I get an exception similar to:

SQLException: Cannot connect to MySQL server on host:3306.
Is there a MySQL server running on the machine/port you
are trying to connect to?

(java.security.AccessControlException)
SQLState: 08S01
VendorError: 0 

Answer:

Either you're running an Applet, your MySQL server has been installed with the "--skip-networking" option set, or your MySQL server has a firewall sitting in front of it.

Applets can only make network connections back to the machine that runs the web server that served the .class files for the applet. This means that MySQL must run on the same machine (or you must have some sort of port re-direction) for this to work. This also means that you will not be able to test applets from your local file system, you must always deploy them to a web server.

MySQL Connector/J can only communicate with MySQL using TCP/IP, as Java does not support Unix domain sockets. TCP/IP communication with MySQL might be affected if MySQL was started with the "--skip-networking" flag, or if it is firewalled.

If MySQL has been started with the "--skip-networking" option set (the Debian Linux package of MySQL server does this for example), you need to comment it out in the file /etc/mysql/my.cnf or /etc/my.cnf. Of course your my.cnf file might also exist in the directory of your MySQL server, or anywhere else (depending on how MySQL was compiled for your system). Binaries created by MySQL AB always look in /etc/my.cnf and [datadir]/my.cnf. If your MySQL server has been firewalled, you will need to have the firewall configured to allow TCP/IP connections from the host where your Java code is running to the MySQL server on the port that MySQL is listening to (by default, 3306).

24.3.5.3.4:

Question:

I have a servlet/application that works fine for a day, and then stops working overnight

Answer:

MySQL closes connections after 8 hours of inactivity. You either need to use a connection pool that handles stale connections or use the "autoReconnect" parameter (see Section 23.3.4.1, “Driver/Datasource Class Names, URL Syntax and Configuration Properties for Connector/J”).

Also, you should be catching SQLExceptions in your application and dealing with them, rather than propagating them all the way until your application exits, this is just good programming practice. MySQL Connector/J will set the SQLState (see in your APIDOCS) to "08S01" when it encounters network-connectivity issues during the processing of a query. Your application code should then attempt to re-connect to MySQL at this point.

The following (simplistic) example shows what code that can handle these exceptions might look like:

Example 23.12. Example of transaction with retry logic

public void doBusinessOp() throws SQLException {
        Connection conn = null;
        Statement stmt = null;
        ResultSet rs = null;

        //
        // How many times do you want to retry the transaction
        // (or at least _getting_ a connection)?
        //
        int retryCount = 5;

        boolean transactionCompleted = false;

        do {
            try {
                conn = getConnection(); // assume getting this from a
                                        // javax.sql.DataSource, or the
                                        // java.sql.DriverManager

                conn.setAutoCommit(false);

                //
                // Okay, at this point, the 'retry-ability' of the
                // transaction really depends on your application logic,
                // whether or not you're using autocommit (in this case
                // not), and whether you're using transacational storage
                // engines
                //
                // For this example, we'll assume that it's _not_ safe
                // to retry the entire transaction, so we set retry count
                // to 0 at this point
                //
                // If you were using exclusively transaction-safe tables,
                // or your application could recover from a connection going
                // bad in the middle of an operation, then you would not
                // touch 'retryCount' here, and just let the loop repeat
                // until retryCount == 0.
                //
                retryCount = 0;

                stmt = conn.createStatement();

                String query = "SELECT foo FROM bar ORDER BY baz";

                rs = stmt.executeQuery(query);

                while (rs.next()) {
                }

                rs.close();
                rs = null;

                stmt.close();
                stmt = null;

                conn.commit();
                conn.close();
                conn = null;

                transactionCompleted = true;
            } catch (SQLException sqlEx) {

                //
                // The two SQL states that are 'retry-able' are 08S01
                // for a communications error, and 40001 for deadlock.
                //
                // Only retry if the error was due to a stale connection,
                // communications problem or deadlock
                //

                String sqlState = sqlEx.getSQLState();

                if ("08S01".equals(sqlState) || "40001".equals(sqlState)) {
                    retryCount--;
                } else {
                    retryCount = 0;
                }
            } finally {
                if (rs != null) {
                    try {
                        rs.close();
                    } catch (SQLException sqlEx) {
                        // You'd probably want to log this . . .
                    }
                }

                if (stmt != null) {
                    try {
                        stmt.close();
                    } catch (SQLException sqlEx) {
                        // You'd probably want to log this as well . . .
                    }
                }

                if (conn != null) {
                    try {
                        //
                        // If we got here, and conn is not null, the
                        // transaction should be rolled back, as not
                        // all work has been done

                        try {
                            conn.rollback();
                        } finally {
                            conn.close();
                        }
                    } catch (SQLException sqlEx) {
                        //
                        // If we got an exception here, something
                        // pretty serious is going on, so we better
                        // pass it up the stack, rather than just
                        // logging it. . .

                        throw sqlEx;
                    }
                }
            }
        } while (!transactionCompleted && (retryCount > 0));
    }

Note.  Use of the option is not recommended because there is no safe method of reconnecting to the MySQL server without risking some corruption of the connection state or database state information. Instead, you should use a connection pool which will enable your application to connect to the MySQL server using an available connection from the pool. The facility is deprecated, and may be removed in a future release.

24.3.5.3.5:

Question:

I'm trying to use JDBC-2.0 updatable result sets, and I get an exception saying my result set is not updatable.

Answer:

Because MySQL does not have row identifiers, MySQL Connector/J can only update result sets that have come from queries on tables that have at least one primary key, the query must select every primary key and the query can only span one table (that is, no joins). This is outlined in the JDBC specification.

23.3.6. Connector/J Support

23.3.6.1. Connector/J Community Support

MySQL AB provides assistance to the user community by means of its mailing lists. For Connector/J related issues, you can get help from experienced users by using the MySQL and Java mailing list. Archives and subscription information is available online at http://lists.mysql.com/java.

For information about subscribing to MySQL mailing lists or to browse list archives, visit http://lists.mysql.com/. See Section 1.7.1, “MySQL Mailing Lists”.

Community support from experienced users is also available through the JDBC Forum. You may also find help from other users in the other MySQL Forums, located at http://forums.mysql.com. See Section 1.7.2, “MySQL Community Support at the MySQL Forums”.

23.3.6.2. How to Report Connector/J Bugs or Problems

The normal place to report bugs is http://bugs.mysql.com/, which is the address for our bugs database. This database is public, and can be browsed and searched by anyone. If you log in to the system, you will also be able to enter new reports.

If you have found a sensitive security bug in MySQL, you can send email to security_at_mysql.com.

Writing a good bug report takes patience, but doing it right the first time saves time both for us and for yourself. A good bug report, containing a full test case for the bug, makes it very likely that we will fix the bug in the next release.

This section will help you write your report correctly so that you don't waste your time doing things that may not help us much or at all.

If you have a repeatable bug report, please report it to the bugs database at http://bugs.mysql.com/. Any bug that we are able to repeat has a high chance of being fixed in the next MySQL release.

To report other problems, you can use one of the MySQL mailing lists.

Remember that it is possible for us to respond to a message containing too much information, but not to one containing too little. People often omit facts because they think they know the cause of a problem and assume that some details don't matter.

A good principle is this: If you are in doubt about stating something, state it. It is faster and less troublesome to write a couple more lines in your report than to wait longer for the answer if we must ask you to provide information that was missing from the initial report.

The most common errors made in bug reports are (a) not including the version number of Connector/J or MySQL used, and (b) not fully describing the platform on which Connector/J is installed (including the JVM version, and the platform type and version number that MySQL itself is installed on).

This is highly relevant information, and in 99 cases out of 100, the bug report is useless without it. Very often we get questions like, “Why doesn't this work for me?” Then we find that the feature requested wasn't implemented in that MySQL version, or that a bug described in a report has already been fixed in newer MySQL versions.

Sometimes the error is platform-dependent; in such cases, it is next to impossible for us to fix anything without knowing the operating system and the version number of the platform.

If at all possible, you should create a repeatable, stanalone testcase that doesn't involve any third-party classes.

To streamline this process, we ship a base class for testcases with Connector/J, named ''. To create a testcase for Connector/J using this class, create your own class that inherits from and override the methods , and .

In the method, create code that creates your tables, and populates them with any data needed to demonstrate the bug.

In the method, create code that demonstrates the bug using the tables and data you created in the method.

In the method, drop any tables you created in the method.

In any of the above three methods, you should use one of the variants of the method to create a JDBC connection to MySQL:

  • - Provides a connection to the JDBC URL specified in . If a connection already exists, that connection is returned, otherwise a new connection is created.

  • - Use this if you need to get a new connection for your bug report (i.e. there's more than one connection involved).

  • - Returns a connection using the given URL.

  • - Returns a connection using the given URL and properties.

If you need to use a JDBC URL that is different from 'jdbc:mysql:///test', override the method as well.

Use the and methods to create conditions that must be met in your testcase demonstrating the behavior you are expecting (vs. the behavior you are observing, which is why you are most likely filing a bug report).

Finally, create a method that creates a new instance of your testcase, and calls the method:

public static void main(String[] args) throws Exception {
      new MyBugReport().run();
 }

Once you have finished your testcase, and have verified that it demonstrates the bug you are reporting, upload it with your bug report to http://bugs.mysql.com/.

23.3.6.3. Connector/J Change History

The Connector/J Change History (Changelog) is located with the main Changelog for MySQL. See Section D.5, “MySQL Connector/J Change History”.