DispatchAction class

The DispatchAction class provides a mechanism for modularizing a set of related functions into a single action, and thus eliminates the need to create separate, independent actions for each function. For example, consider a set of related functions for adding a user, updating a user, and removing a user. Instead of creating an AddUserAction class, an UpdateUserAction class, and a RemoveUserAction class, by extending DispatchAction, you can create one UserAction class that has three methods: add( ), update( ), and remove( ). At run time, DispatchAction manages routing requests to the appropriate method in its subclass. DispatchAction determines which method to call based on the value of a request parameter that is passed to it from the incoming request.

To use DispatchAction, you must create a subclass from it and provide a set of methods that will be called to process requests. Additionally, you have to set up for the action an action mapping that specifies the name of a request parameter that will be used to select which method should be called for each request.

 Following is an example UserAction class that extends DispatchAction:

package pack.nk;

import javax.servlet.http.HttpServletRequest;

import javax.servlet.http.HttpServletResponse;

import org.apache.struts.action.ActionForm;

import org.apache.struts.action.ActionForward;

import org.apache.struts.action.ActionMapping;

import org.apache.struts.actions.DispatchAction;

public class UserAction extends DispatchAction

{

  public ActionForward add(ActionMapping mapping,

    ActionForm form,

    HttpServletRequest request,

    HttpServletResponse response)

    throws Exception

  {

    // Add user.

    …

    return new ActionForward("success");

  }

  public ActionForward update(ActionMapping mapping,

    ActionForm form,

    HttpServletRequest request,

    HttpServletResponse response)

    throws Exception

  {

    // Update user.

    …

    return new ActionForward("success");

  }

  public ActionForward remove(ActionMapping mapping,

    ActionForm form,

    HttpServletRequest request,

    HttpServletResponse response)

    throws Exception

  {

    // Remove user.

    …

    return new ActionForward("success");

  }

}

<action-mappings>

  <action path="/User"

          type="pack.nk.UserAction"

     parameter="function"/>

</action-mappings>

The value specified with the parameter attribute of the action tag will be used as the name of a request parameter that will contain the name of a method to invoke for handling the request.