Apache Struts API Documentation: Class ActionDispatcher

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org.apache.struts.actions Class ActionDispatcher

java.lang.Object
  |
  +--org.apache.struts.actions.ActionDispatcher

public class ActionDispatcher
extends java.lang.Object

Action helper class that dispatches to a public method in an Action.

This class is provided as an alternative mechanism to using DispatchAction and its various flavours and means Dispatch behaviour can be easily implemented into any Action without having to inherit from a particular super Action.

To implement dispatch behaviour in an Action class, create your custom Action as follows, along with the methods you require (and optionally "cancelled" and "unspecified" methods):

   public class MyCustomAction extends Action {
 
       protected ActionDispatcher dispatcher
                = new ActionDispatcher(this, ActionDispatcher.MAPPING_FLAVOR);
 
       public ActionForward execute(ActionMapping mapping,
                                    ActionForm form,
                                    HttpServletRequest request,
                                    HttpServletResponse response)
                           throws Exception {
           return dispatcher.execute(mapping, form, request, response);
       }
   }

It provides three flavours of determing the name of the method:

DEFAULT_FLAVOR - uses the parameter specified in the struts-config.xml to get the method name from the Request (equivalent to DispatchAction except uses "method" as a default if the parameter is not specified in the struts-config.xml).

DISPATCH_FLAVOR - uses the parameter specified in the struts-config.xml to get the method name from the Request (equivalent to DispatchAction).

MAPPING_FLAVOR - uses the parameter specified in the struts-config.xml as the method name (equivalent to MappingDispatchAction).

Since:: Struts 1.2.7
Version:: $Revision: 164746 $ $Date: 2005-04-26 06:41:28 +0100 (Tue, 26 Apr 2005) $

Field Summary
`protected Action`	`actionInstance` The associated Action to dispatch to.
`protected java.lang.Class`	`clazz` The Class instance of this `DispatchAction` class.
`static int`	`DEFAULT_FLAVOR` Indicates "default" dispatch flavor
`static int`	`DISPATCH_FLAVOR` Indicates flavor compatible with DispatchAction
`protected int`	`flavor` Indicates dispatch flavor
`protected static org.apache.commons.logging.Log`	`log` Commons Logging instance.
`static int`	`MAPPING_FLAVOR` Indicates "mapping" dispatch flavor
`protected static MessageResources`	`messages` The message resources for this package.
`protected java.util.HashMap`	`methods` The set of Method objects we have introspected for this class, keyed by method name.
`protected java.lang.Class[]`	`types` The set of argument type classes for the reflected method call.

Constructor Summary
`ActionDispatcher(Action actionInstance)`
`ActionDispatcher(Action actionInstance, int flavor)`

Method Summary
`protected ActionForward`	`cancelled(ActionMapping mapping, ActionForm form, javax.servlet.http.HttpServletRequest request, javax.servlet.http.HttpServletResponse response)` Dispatches to the target class' cancelled method, if present, otherwise returns null.
`protected ActionForward`	`dispatchMethod(ActionMapping mapping, ActionForm form, javax.servlet.http.HttpServletRequest request, javax.servlet.http.HttpServletResponse response, java.lang.String name)` Dispatch to the specified method.
`protected ActionForward`	`dispatchMethod(ActionMapping mapping, ActionForm form, javax.servlet.http.HttpServletRequest request, javax.servlet.http.HttpServletResponse response, java.lang.String name, java.lang.reflect.Method method)` Dispatch to the specified method.
`ActionForward`	`execute(ActionMapping mapping, ActionForm form, javax.servlet.http.HttpServletRequest request, javax.servlet.http.HttpServletResponse response)` Process the specified HTTP request, and create the corresponding HTTP response (or forward to another web component that will create it).
`protected java.lang.reflect.Method`	`getMethod(java.lang.String name)` Introspect the current class to identify a method of the specified name that accepts the same parameter types as the `execute` method does.
`protected java.lang.String`	`getMethodName(ActionMapping mapping, ActionForm form, javax.servlet.http.HttpServletRequest request, javax.servlet.http.HttpServletResponse response, java.lang.String parameter)` Returns the method name, given a parameter's value.
`protected java.lang.String`	`getParameter(ActionMapping mapping, ActionForm form, javax.servlet.http.HttpServletRequest request, javax.servlet.http.HttpServletResponse response)` Returns the parameter value as influenced by the selected `flavor` specified for this `ActionDispatcher`.
`protected boolean`	`isCancelled(javax.servlet.http.HttpServletRequest request)` Returns `true` if the current form's cancel button was pressed.
`protected ActionForward`	`unspecified(ActionMapping mapping, ActionForm form, javax.servlet.http.HttpServletRequest request, javax.servlet.http.HttpServletResponse response)` Dispatches to the target class' `unspecified` method, if present, otherwise throws a ServletException.

Methods inherited from class java.lang.Object

, clone, equals, finalize, getClass, hashCode, notify, notifyAll, registerNatives, toString, wait, wait, wait

Field Detail

DEFAULT_FLAVOR

public static final int DEFAULT_FLAVOR

Indicates "default" dispatch flavor

MAPPING_FLAVOR

public static final int MAPPING_FLAVOR

Indicates "mapping" dispatch flavor

DISPATCH_FLAVOR

public static final int DISPATCH_FLAVOR

Indicates flavor compatible with DispatchAction

actionInstance

protected Action actionInstance

The associated Action to dispatch to.

flavor

protected int flavor

Indicates dispatch flavor

clazz

protected java.lang.Class clazz

The Class instance of this DispatchAction class.

log

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

Commons Logging instance.

messages

protected static MessageResources messages

The message resources for this package.

methods

protected java.util.HashMap methods

The set of Method objects we have introspected for this class, keyed by method name. This collection is populated as different methods are called, so that introspection needs to occur only once per method name.

types

protected java.lang.Class[] types

The set of argument type classes for the reflected method call. These are the same for all calls, so calculate them only once.

Constructor Detail

ActionDispatcher

public ActionDispatcher(Action actionInstance)

ActionDispatcher

public ActionDispatcher(Action actionInstance,
                        int flavor)

Method Detail

execute

public ActionForward execute(ActionMapping mapping,
                             ActionForm form,
                             javax.servlet.http.HttpServletRequest request,
                             javax.servlet.http.HttpServletResponse response)
                      throws java.lang.Exception

Process the specified HTTP request, and create the corresponding HTTP response (or forward to another web component that will create it). Return an ActionForward instance describing where and how control should be forwarded, or null if the response has already been completed.

Parameters:: mapping - The ActionMapping used to select this instance; form - The optional ActionForm bean for this request (if any); request - The HTTP request we are processing; response - The HTTP response we are creating
Throws:: java.lang.Exception - if an exception occurs

unspecified

protected ActionForward unspecified(ActionMapping mapping,
                                    ActionForm form,
                                    javax.servlet.http.HttpServletRequest request,
                                    javax.servlet.http.HttpServletResponse response)
                             throws java.lang.Exception

Dispatches to the target class' unspecified method, if present, otherwise throws a ServletException. Classes utilizing ActionDispatcher should provide an unspecified method if they wish to provide behavior different than throwing a ServletException..

cancelled

protected ActionForward cancelled(ActionMapping mapping,
                                  ActionForm form,
                                  javax.servlet.http.HttpServletRequest request,
                                  javax.servlet.http.HttpServletResponse response)
                           throws java.lang.Exception

Dispatches to the target class' cancelled method, if present, otherwise returns null. Classes utilizing ActionDispatcher should provide a cancelled method if they wish to provide behavior different than returning null.

dispatchMethod

protected ActionForward dispatchMethod(ActionMapping mapping,
                                       ActionForm form,
                                       javax.servlet.http.HttpServletRequest request,
                                       javax.servlet.http.HttpServletResponse response,
                                       java.lang.String name)
                                throws java.lang.Exception

Dispatch to the specified method.

dispatchMethod

protected ActionForward dispatchMethod(ActionMapping mapping,
                                       ActionForm form,
                                       javax.servlet.http.HttpServletRequest request,
                                       javax.servlet.http.HttpServletResponse response,
                                       java.lang.String name,
                                       java.lang.reflect.Method method)
                                throws java.lang.Exception

Dispatch to the specified method.

getMethod

protected java.lang.reflect.Method getMethod(java.lang.String name)
                                      throws java.lang.NoSuchMethodException

Introspect the current class to identify a method of the specified name that accepts the same parameter types as the execute method does.

Parameters:: name - Name of the method to be introspected
Throws:: java.lang.NoSuchMethodException - if no such method can be found

getParameter

protected java.lang.String getParameter(ActionMapping mapping,
                                        ActionForm form,
                                        javax.servlet.http.HttpServletRequest request,
                                        javax.servlet.http.HttpServletResponse response)
                                 throws java.lang.Exception

Returns the parameter value as influenced by the selected flavor specified for this ActionDispatcher.

Parameters:: mapping - The ActionMapping used to select this instance; form - The optional ActionForm bean for this request (if any); request - The HTTP request we are processing; response - The HTTP response we are creating
Returns:: The ActionMapping parameter's value

getMethodName

protected java.lang.String getMethodName(ActionMapping mapping,
                                         ActionForm form,
                                         javax.servlet.http.HttpServletRequest request,
                                         javax.servlet.http.HttpServletResponse response,
                                         java.lang.String parameter)
                                  throws java.lang.Exception

Returns the method name, given a parameter's value.

Parameters:: mapping - The ActionMapping used to select this instance; form - The optional ActionForm bean for this request (if any); request - The HTTP request we are processing; response - The HTTP response we are creating; parameter - The ActionMapping parameter's name
Returns:: The method's name.

isCancelled

protected boolean isCancelled(javax.servlet.http.HttpServletRequest request)

Returns true if the current form's cancel button was pressed. This method will check if the Globals.CANCEL_KEY request attribute has been set, which normally occurs if the cancel button generated by CancelTag was pressed by the user in the current request. If true, validation performed by an ActionForm's validate() method will have been skipped by the controller servlet.

Parameters:: request - The servlet request we are processing
See Also:: CancelTag