Apache Struts API Documentation: Class ActionServlet

org.apache.struts.action Class ActionServlet

java.lang.Object
  |
  +--javax.servlet.GenericServlet
        |
        +--javax.servlet.http.HttpServlet
              |
              +--org.apache.struts.action.ActionServlet

All Implemented Interfaces:

java.io.Serializable, javax.servlet.Servlet, javax.servlet.ServletConfig

Direct Known Subclasses:

RedeployableActionServlet

public class ActionServlet

extends javax.servlet.http.HttpServlet

ActionServlet provides the "controller" in the Model-View-Controller (MVC) design pattern for web applications that is commonly known as "Model 2". This nomenclature originated with a description in the JavaServerPages Specification, version 0.92, and has persisted ever since (in the absence of a better name).

Generally, a "Model 2" application is architected as follows:

• The user interface will generally be created with server pages, which will not themselves contain any business logic. These pages represent the "view" component of an MVC architecture.
• Forms and hyperlinks in the user interface that require business logic to be executed will be submitted to a request URI that is mapped to this servlet.
• There can be one instance of this servlet class, which receives and processes all requests that change the state of a user's interaction with the application. The servlet delegates the handling of a request to a RequestProcessor object. This component represents the "controller" component of an MVC architecture.
• The RequestProcessor selects and invokes an Action class to perform the requested business logic, or delegates the response to another resource.
• The Action classes can manipulate the state of the application's interaction with the user, typically by creating or modifying JavaBeans that are stored as request or session attributes (depending on how long they need to be available). Such JavaBeans represent the "model" component of an MVC architecture.
• Instead of producing the next page of the user interface directly, Action classes generally return an ActionForward to indicate which resource should handle the response. If the Action does not return null, the RequestProcessor forwards or redirects to the specified resource (by utilizing RequestDispatcher.forward or Response.sendRedirect) so as to produce the next page of the user interface.

The standard version of RequestsProcessor implements the following logic for each incoming HTTP request. You can override some or all of this functionality by subclassing this object and implementing your own version of the processing.

• Identify, from the incoming request URI, the substring that will be used to select an action procedure.
• Use this substring to map to the Java class name of the corresponding action class (an implementation of the Action interface).
• If this is the first request for a particular Action class, instantiate an instance of that class and cache it for future use.
• Optionally populate the properties of an ActionForm bean associated with this mapping.
• Call the execute method of this Action class, passing on a reference to the mapping that was used, the relevant form-bean (if any), and the request and the response that were passed to the controller by the servlet container (thereby providing access to any specialized properties of the mapping itself as well as to the ServletContext).

The standard version of ActionServlet is configured based on the following servlet initialization parameters, which you will specify in the web application deployment descriptor (/WEB-INF/web.xml) for your application. Subclasses that specialize this servlet are free to define additional initialization parameters.

• config - Comma-separated list of context-relative path(s) to the XML resource(s) containing the configuration information for the default module. (Multiple files support since Struts 1.1) [/WEB-INF/struts-config.xml].
• config/${module} - Comma-separated list of Context-relative path(s) to the XML resource(s) containing the configuration information for the module that will use the specified prefix (/${module}). This can be repeated as many times as required for multiple modules. (Since Struts 1.1)
• configFactory - The Java class name of the ModuleConfigFactory used to create the implementation of the ModuleConfig interface. [org.apache.struts.config.impl.DefaultModuleConfigFactory]
• convertNull - Force simulation of the Struts 1.0 behavior when populating forms. If set to true, the numeric Java wrapper class types (like java.lang.Integer) will default to null (rather than 0). (Since Struts 1.1) [false]
• rulesets - Comma-delimited list of fully qualified classnames of additional org.apache.commons.digester.RuleSet instances that should be added to the Digester that will be processing struts-config.xml files. By default, only the RuleSet for the standard configuration elements is loaded. (Since Struts 1.1)
• validating - Should we use a validating XML parser to process the configuration file (strongly recommended)? [true]

Version:

$Rev: 164530 $ $Date: 2005-04-25 04:11:07 +0100 (Mon, 25 Apr 2005) $

See Also:

Serialized Form

config

protected java.lang.String config

Comma-separated list of context-relative path(s) to our configuration resource(s) for the default module.

configDigester

protected org.apache.commons.digester.Digester configDigester

The Digester used to produce ModuleConfig objects from a Struts configuration file.

Since:

Struts 1.1

convertNull

protected boolean convertNull

The flag to request backwards-compatible conversions for form bean properties of the Java wrapper class types.

Since:

Struts 1.1

dataSources

protected org.apache.commons.collections.FastHashMap dataSources

The JDBC data sources that has been configured for this module, if any, keyed by the servlet context attribute under which they are stored.

internal

protected MessageResources internal

The resources object for our internal resources.

internalName

protected java.lang.String internalName

The Java base name of our internal resources.

Since:

Struts 1.1

log

protected static org.apache.commons.logging.Log log

Commons Logging instance.

Since:

Struts 1.1

processor

protected RequestProcessor processor

The RequestProcessor instance we will use to process all incoming requests.

Since:

Struts 1.1

registrations

protected java.lang.String[] registrations

The set of public identifiers, and corresponding resource names, for the versions of the configuration file DTDs that we know about. There MUST be an even number of Strings in this list!

servletMapping

protected java.lang.String servletMapping

The URL pattern to which we are mapped in our web application deployment descriptor.

servletName

protected java.lang.String servletName

The servlet name under which we are registered in our web application deployment descriptor.

ActionServlet

public ActionServlet()

destroy

public void destroy()

Gracefully shut down this controller servlet, releasing any resources that were allocated at initialization.

Overrides:

destroy in class javax.servlet.GenericServlet

init

public void init()
          throws javax.servlet.ServletException

Initialize this servlet. Most of the processing has been factored into support methods so that you can override particular functionality at a fairly granular level.

Overrides:

init in class javax.servlet.GenericServlet

Throws:

javax.servlet.ServletException - if we cannot configure ourselves correctly

initModulePrefixes

protected void initModulePrefixes(javax.servlet.ServletContext context)

Saves a String[] of module prefixes in the ServletContext under Globals.MODULE_PREFIXES_KEY. NOTE - the "" prefix for the default module is not included in this list.

Parameters:

context - The servlet context.

Since:

Struts 1.2

doGet

public void doGet(javax.servlet.http.HttpServletRequest request,
                  javax.servlet.http.HttpServletResponse response)
           throws java.io.IOException,
                  javax.servlet.ServletException

Process an HTTP "GET" request.

Overrides:

doGet in class javax.servlet.http.HttpServlet

Parameters:

request - The servlet request we are processing

response - The servlet response we are creating

Throws:

java.io.IOException - if an input/output error occurs

javax.servlet.ServletException - if a servlet exception occurs

doPost

public void doPost(javax.servlet.http.HttpServletRequest request,
                   javax.servlet.http.HttpServletResponse response)
            throws java.io.IOException,
                   javax.servlet.ServletException

Process an HTTP "POST" request.

Overrides:

doPost in class javax.servlet.http.HttpServlet

Parameters:

request - The servlet request we are processing

response - The servlet response we are creating

Throws:

java.io.IOException - if an input/output error occurs

javax.servlet.ServletException - if a servlet exception occurs

addServletMapping

public void addServletMapping(java.lang.String servletName,
                              java.lang.String urlPattern)

Remember a servlet mapping from our web application deployment descriptor, if it is for this servlet.

Parameters:

servletName - The name of the servlet being mapped

urlPattern - The URL pattern to which this servlet is mapped

getInternal

public MessageResources getInternal()

Return the MessageResources instance containing our internal message strings.

Since:

Struts 1.1

destroyModules

protected void destroyModules()

Gracefully terminate use of any modules associated with this application (if any).

Since:

Struts 1.1

destroyConfigDigester

protected void destroyConfigDigester()

Gracefully release any configDigester instance that we have created.

Since:

Struts 1.1

destroyInternal

protected void destroyInternal()

Gracefully terminate use of the internal MessageResources.

getModuleConfig

protected ModuleConfig getModuleConfig(javax.servlet.http.HttpServletRequest request)

Return the module configuration object for the currently selected module.

Parameters:

request - The servlet request we are processing

Since:

Struts 1.1

getRequestProcessor

protected RequestProcessor getRequestProcessor(ModuleConfig config)
                                        throws javax.servlet.ServletException

Look up and return the RequestProcessor responsible for the specified module, creating a new one if necessary.

Parameters:

config - The module configuration for which to acquire and return a RequestProcessor.

Throws:

javax.servlet.ServletException - if we cannot instantiate a RequestProcessor instance

Since:

Struts 1.1

getProcessorForModule

private RequestProcessor getProcessorForModule(ModuleConfig config)

Returns the RequestProcessor for the given module or null if one does not exist. This method will not create a RequestProcessor.

Parameters:

config - The ModuleConfig.

initModuleConfigFactory

protected void initModuleConfigFactory()

Initialize the factory used to create the module configuration.

Since:

Struts 1.2

initModuleConfig

protected ModuleConfig initModuleConfig(java.lang.String prefix,
                                        java.lang.String paths)
                                 throws javax.servlet.ServletException

Initialize the module configuration information for the specified module.

Parameters:

prefix - Module prefix for this module

paths - Comma-separated list of context-relative resource path(s) for this modules's configuration resource(s)

Throws:

javax.servlet.ServletException - if initialization cannot be performed

Since:

Struts 1.1

parseModuleConfigFile

protected void parseModuleConfigFile(org.apache.commons.digester.Digester digester,
                                     java.lang.String path)
                              throws javax.servlet.UnavailableException

Parses one module config file.

Parameters:

digester - Digester instance that does the parsing

path - The path to the config file to parse.

Throws:

javax.servlet.UnavailableException - if file cannot be read or parsed

Since:

Struts 1.2

handleConfigException

private void handleConfigException(java.lang.String path,
                                   java.lang.Exception e)
                            throws javax.servlet.UnavailableException

Simplifies exception handling in the parseModuleConfigFile method.

Parameters:

path -  

e -  

Throws:

javax.servlet.UnavailableException - as a wrapper around Exception

initModuleDataSources

protected void initModuleDataSources(ModuleConfig config)
                              throws javax.servlet.ServletException

Initialize the data sources for the specified module.

Parameters:

config - ModuleConfig information for this module

Throws:

javax.servlet.ServletException - if initialization cannot be performed

Since:

Struts 1.1

initModulePlugIns

protected void initModulePlugIns(ModuleConfig config)
                          throws javax.servlet.ServletException

Initialize the plug ins for the specified module.

Parameters:

config - ModuleConfig information for this module

Throws:

javax.servlet.ServletException - if initialization cannot be performed

Since:

Struts 1.1

initModuleMessageResources

protected void initModuleMessageResources(ModuleConfig config)
                                   throws javax.servlet.ServletException

Initialize the application MessageResources for the specified module.

Parameters:

config - ModuleConfig information for this module

Throws:

javax.servlet.ServletException - if initialization cannot be performed

Since:

Struts 1.1

initConfigDigester

protected org.apache.commons.digester.Digester initConfigDigester()
                                                           throws javax.servlet.ServletException

Create (if needed) and return a new Digester instance that has been initialized to process Struts module configuration files and configure a corresponding ModuleConfig object (which must be pushed on to the evaluation stack before parsing begins).

Throws:

javax.servlet.ServletException - if a Digester cannot be configured

Since:

Struts 1.1

addRuleSets

private void addRuleSets()
                  throws javax.servlet.ServletException

Add any custom RuleSet instances to configDigester that have been specified in the rulesets init parameter.

Throws:

javax.servlet.ServletException -  

isValidating

private boolean isValidating()

Check the status of the validating initialization parameter.

Returns:

true if the module Digester should validate.

initInternal

protected void initInternal()
                     throws javax.servlet.ServletException

Initialize our internal MessageResources bundle.

Throws:

javax.servlet.ServletException - if we cannot initialize these resources

initOther

protected void initOther()
                  throws javax.servlet.ServletException

Initialize other global characteristics of the controller servlet.

Throws:

javax.servlet.ServletException - if we cannot initialize these resources

initServlet

protected void initServlet()
                    throws javax.servlet.ServletException

Initialize the servlet mapping under which our controller servlet is being accessed. This will be used in the &html;:form> tag to generate correct destination URLs for form submissions.

Throws:

javax.servlet.ServletException - if error happens while scanning web.xml

process

protected void process(javax.servlet.http.HttpServletRequest request,
                       javax.servlet.http.HttpServletResponse response)
                throws java.io.IOException,
                       javax.servlet.ServletException

Perform the standard request processing for this request, and create the corresponding response.

Parameters:

request - The servlet request we are processing

response - The servlet response we are creating

Throws:

java.io.IOException - if an input/output error occurs

javax.servlet.ServletException - if a servlet exception is thrown