Apache Struts API Documentation: Class DispatchAction

org.apache.struts.actions Class DispatchAction

java.lang.Object
  |
  +--org.apache.struts.action.Action
        |
        +--org.apache.struts.actions.DispatchAction

Direct Known Subclasses:

LookupDispatchAction, MappingDispatchAction

public abstract class DispatchAction

extends Action

An abstract Action that dispatches to a public method that is named by the request parameter whose name is specified by the parameter property of the corresponding ActionMapping. This Action is useful for developers who prefer to combine many similar actions into a single Action class, in order to simplify their application design.

To configure the use of this action in your struts-config.xml file, create an entry like this:

which will use the value of the request parameter named "method" to pick the appropriate "execute" method, which must have the same signature (other than method name) of the standard Action.execute method. For example, you might have the following three methods in the same action:

• public ActionForward delete(ActionMapping mapping, ActionForm form, HttpServletRequest request, HttpServletResponse response) throws Exception
• public ActionForward insert(ActionMapping mapping, ActionForm form, HttpServletRequest request, HttpServletResponse response) throws Exception
• public ActionForward update(ActionMapping mapping, ActionForm form, HttpServletRequest request, HttpServletResponse response) throws Exception

and call one of the methods with a URL like this:

NOTE - All of the other mapping characteristics of this action must be shared by the various handlers. This places some constraints over what types of handlers may reasonably be packaged into the same DispatchAction subclass.

NOTE - If the value of the request parameter is empty, a method named unspecified is called. The default action is to throw an exception. If the request was cancelled (a html:cancel button was pressed), the custom handler cancelled will be used instead. You can also override the getMethodName method to override the action's default handler selection.

Version:

$Rev: 54929 $ $Date: 2004-10-16 17:38:42 +0100 (Sat, 16 Oct 2004) $

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.

DispatchAction

public DispatchAction()

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.

Overrides:

execute in class Action

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

Method which is dispatched to when there is no value for specified request parameter included in the request. Subclasses of DispatchAction should override this method if they wish to provide default 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

Method which is dispatched to when the request is a cancel button submit. Subclasses of DispatchAction should override this method if they wish to provide default behavior different than returning null.

Since:

Struts 1.2.0

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.

Since:

Struts 1.1

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

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.

Since:

Struts 1.2.0