DataHandler (Java EE 5 SDK)

javax.activation Class DataHandler

java.lang.Object
  javax.activation.DataHandler

所有已实现的接口:

Transferable

public class DataHandler

extends Object

implements Transferable

The DataHandler class provides a consistent interface to data available in many different sources and formats. It manages simple stream to string conversions and related operations using DataContentHandlers. It provides access to commands that can operate on the data. The commands are found using a CommandMap.

DataHandler and the Transferable Interface

DataHandler implements the Transferable interface so that data can be used in AWT data transfer operations, such as cut and paste and drag and drop. The implementation of the Transferable interface relies on the availability of an installed DataContentHandler object corresponding to the MIME type of the data represented in the specific instance of the DataHandler.

DataHandler and CommandMaps

The DataHandler keeps track of the current CommandMap that it uses to service requests for commands (getCommand, getAllCommands, getPreferredCommands). Each instance of a DataHandler may have a CommandMap associated with it using the setCommandMap method. If a CommandMap was not set, DataHandler calls the getDefaultCommandMap method in CommandMap and uses the value it returns. See CommandMap for more information.

DataHandler and URLs

The current DataHandler implementation creates a private instance of URLDataSource when it is constructed with a URL.

另请参见:

CommandMap, DataContentHandler, DataSource, URLDataSource

DataHandler

public DataHandler(DataSource ds)

Create a DataHandler instance referencing the specified DataSource. The data exists in a byte stream form. The DataSource will provide an InputStream to access the data.

参数:

ds - the DataSource

DataHandler

public DataHandler(Object obj,
                   String mimeType)

Create a DataHandler instance representing an object of this MIME type. This constructor is used when the application already has an in-memory representation of the data in the form of a Java Object.

参数:

obj - the Java Object

mimeType - the MIME type of the object

DataHandler

public DataHandler(URL url)

Create a DataHandler instance referencing a URL. The DataHandler internally creates a URLDataSource instance to represent the URL.

参数:

url - a URL object

getDataSource

public DataSource getDataSource()

Return the DataSource associated with this instance of DataHandler.

For DataHandlers that have been instantiated with a DataSource, this method returns the DataSource that was used to create the DataHandler object. In other cases the DataHandler constructs a DataSource from the data used to construct the DataHandler. DataSources created for DataHandlers not instantiated with a DataSource are cached for performance reasons.

返回:

a valid DataSource object for this DataHandler

getName

public String getName()

Return the name of the data object. If this DataHandler was created with a DataSource, this method calls through to the DataSource.getName method, otherwise it returns null.

返回:

the name of the object

getContentType

public String getContentType()

Return the MIME type of this object as retrieved from the source object. Note that this is the full type with parameters.

返回:

the MIME type

getInputStream

public InputStream getInputStream()
                           throws IOException

Get the InputStream for this object.

For DataHandlers instantiated with a DataSource, the DataHandler calls the DataSource.getInputStream method and returns the result to the caller.

For DataHandlers instantiated with an Object, the DataHandler first attempts to find a DataContentHandler for the Object. If the DataHandler can not find a DataContentHandler for this MIME type, it throws an UnsupportedDataTypeException. If it is successful, it creates a pipe and a thread. The thread uses the DataContentHandler's writeTo method to write the stream data into one end of the pipe. The other end of the pipe is returned to the caller. Because a thread is created to copy the data, IOExceptions that may occur during the copy can not be propagated back to the caller. The result is an empty stream.

返回:

the InputStream representing this data

抛出异常:

IOException - if an I/O error occurs

另请参见:

DataContentHandler.writeTo(java.lang.Object, java.lang.String, java.io.OutputStream), UnsupportedDataTypeException

writeTo

public void writeTo(OutputStream os)
             throws IOException

Write the data to an OutputStream.

If the DataHandler was created with a DataSource, writeTo retrieves the InputStream and copies the bytes from the InputStream to the OutputStream passed in.

If the DataHandler was created with an object, writeTo retrieves the DataContentHandler for the object's type. If the DataContentHandler was found, it calls the writeTo method on the DataContentHandler.

参数:

os - the OutputStream to write to

抛出异常:

IOException - if an I/O error occurs

getOutputStream

public OutputStream getOutputStream()
                             throws IOException

Get an OutputStream for this DataHandler to allow overwriting the underlying data. If the DataHandler was created with a DataSource, the DataSource's getOutputStream method is called. Otherwise, null is returned.

返回:

the OutputStream

抛出异常:

IOException

另请参见:

DataSource.getOutputStream(), URLDataSource

getTransferDataFlavors

public DataFlavor[] getTransferDataFlavors()

Return the DataFlavors in which this data is available.

Returns an array of DataFlavor objects indicating the flavors the data can be provided in. The array is usually ordered according to preference for providing the data, from most richly descriptive to least richly descriptive.

The DataHandler attempts to find a DataContentHandler that corresponds to the MIME type of the data. If one is located, the DataHandler calls the DataContentHandler's getTransferDataFlavors method.

If a DataContentHandler can not be located, and if the DataHandler was created with a DataSource (or URL), one DataFlavor is returned that represents this object's MIME type and the java.io.InputStream class. If the DataHandler was created with an object and a MIME type, getTransferDataFlavors returns one DataFlavor that represents this object's MIME type and the object's class.

规范说明:

getTransferDataFlavors in interface Transferable

返回:

an array of data flavors in which this data can be transferred

另请参见:

DataContentHandler.getTransferDataFlavors()

isDataFlavorSupported

public boolean isDataFlavorSupported(DataFlavor flavor)

Returns whether the specified data flavor is supported for this object.

This method iterates through the DataFlavors returned from getTransferDataFlavors, comparing each with the specified flavor.

规范说明:

isDataFlavorSupported in interface Transferable

参数:

flavor - the requested flavor for the data

返回:

true if the data flavor is supported

另请参见:

getTransferDataFlavors()

getTransferData

public Object getTransferData(DataFlavor flavor)
                       throws UnsupportedFlavorException,
                              IOException

Returns an object that represents the data to be transferred. The class of the object returned is defined by the representation class of the data flavor.

For DataHandler's created with DataSources or URLs:

The DataHandler attempts to locate a DataContentHandler for this MIME type. If one is found, the passed in DataFlavor and the type of the data are passed to its getTransferData method. If the DataHandler fails to locate a DataContentHandler and the flavor specifies this object's MIME type and the java.io.InputStream class, this object's InputStream is returned. Otherwise it throws an UnsupportedFlavorException.

For DataHandler's created with Objects:

The DataHandler attempts to locate a DataContentHandler for this MIME type. If one is found, the passed in DataFlavor and the type of the data are passed to its getTransferData method. If the DataHandler fails to locate a DataContentHandler and the flavor specifies this object's MIME type and its class, this DataHandler's referenced object is returned. Otherwise it throws an UnsupportedFlavorException.

规范说明:

getTransferData in interface Transferable

参数:

flavor - the requested flavor for the data

返回:

the object

抛出异常:

UnsupportedFlavorException - if the data could not be converted to the requested flavor

IOException - if an I/O error occurs

另请参见:

ActivationDataFlavor

setCommandMap

public void setCommandMap(CommandMap commandMap)

Set the CommandMap for use by this DataHandler. Setting it to null causes the CommandMap to revert to the CommandMap returned by the CommandMap.getDefaultCommandMap method. Changing the CommandMap, or setting it to null, clears out any data cached from the previous CommandMap.

参数:

commandMap - the CommandMap to use in this DataHandler

另请参见:

CommandMap.setDefaultCommandMap(javax.activation.CommandMap)

getPreferredCommands

public CommandInfo[] getPreferredCommands()

Return the preferred commands for this type of data. This method calls the getPreferredCommands method in the CommandMap associated with this instance of DataHandler. This method returns an array that represents a subset of available commands. In cases where multiple commands for the MIME type represented by this DataHandler are present, the installed CommandMap chooses the appropriate commands.

返回:

the CommandInfo objects representing the preferred commands

另请参见:

CommandMap.getPreferredCommands(java.lang.String)

getAllCommands

public CommandInfo[] getAllCommands()

Return all the commands for this type of data. This method returns an array containing all commands for the type of data represented by this DataHandler. The MIME type for the underlying data represented by this DataHandler is used to call through to the getAllCommands method of the CommandMap associated with this DataHandler.

返回:

the CommandInfo objects representing all the commands

另请参见:

CommandMap.getAllCommands(java.lang.String)

getCommand

public CommandInfo getCommand(String cmdName)

Get the command cmdName. Use the search semantics as defined by the CommandMap installed in this DataHandler. The MIME type for the underlying data represented by this DataHandler is used to call through to the getCommand method of the CommandMap associated with this DataHandler.

参数:

cmdName - the command name

返回:

the CommandInfo corresponding to the command

另请参见:

CommandMap.getCommand(java.lang.String, java.lang.String)

getContent

public Object getContent()
                  throws IOException

Return the data in its preferred Object form.

If the DataHandler was instantiated with an object, return the object.

If the DataHandler was instantiated with a DataSource, this method uses a DataContentHandler to return the content object for the data represented by this DataHandler. If no DataContentHandler can be found for the the type of this data, the DataHandler returns an InputStream for the data.

返回:

the content.

抛出异常:

IOException - if an IOException occurs during this operation.

getBean

public Object getBean(CommandInfo cmdinfo)

A convenience method that takes a CommandInfo object and instantiates the corresponding command, usually a JavaBean component.

This method calls the CommandInfo's getCommandObject method with the ClassLoader used to load the javax.activation.DataHandler class itself.

参数:

cmdinfo - the CommandInfo corresponding to a command

返回:

the instantiated command object

setDataContentHandlerFactory

public static void setDataContentHandlerFactory(DataContentHandlerFactory newFactory)

Sets the DataContentHandlerFactory. The DataContentHandlerFactory is called first to find DataContentHandlers. The DataContentHandlerFactory can only be set once.

If the DataContentHandlerFactory has already been set, this method throws an Error.

参数:

newFactory - the DataContentHandlerFactory

抛出异常:

Error - if the factory has already been defined.

另请参见:

DataContentHandlerFactory

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