Struts MappingDispatchAction Example
Struts MappingDispatch Action (org.apache.struts.actions.MappingDispatchAction)
is one of the Built-in Actions provided along with the struts framework.
The org.apache.struts.actions.MappingDispatchAction
class is a subclass of org.apache.struts.actions.DispatchAction class.
This class enables a user to collect related functions into a single
action class. It needs to create multiple independent actions for
each function. Here in this example you will learn more about Struts MappingDispatchAction
that will help you to grasp the concept better.
Let's develop a class MappingDispatch_Action
which is a sub class of org.apache.struts.actions.MappingDispatchAction
class. This class does not provide an implementation for the
execute() method because DispatchAction class itself
implements this method. MappingDispatchAction
class is much like the DispatchAction class except that it uses a unique
action corresponding to a new request
, to dispatch the methods .
At run time, this class manages to delegate the request to one
of the methods of the derived Action class. Selection of a method depends
on the value of the parameter passed from the incoming
request. MappingDispatchAction
uses this request parameter value and selects a corresponding action
from the different action-mappings defined. This eliminates the need of
creating an instance of ActionForm class.
MappingDispatch_Action class contains multiple
methods ie.. add() , edit() , search() , save() . Here all the
methods are taking the same input parameters but each method returns
a different ActionForward like "add" in
case of add() method , "edit" in case of edit()
etc. Each ActionForward is defined in the struts-config.xml
file (action mapping is shown later in this page).
Developing an Action Class (MappingDispatch_Action.java)
package roseindia.net;
/**
* @author Amit Gupta
* @Web http://www.roseindia.net
* @Email struts@roseindia.net
**/
import java.io.*;
import java.util.*;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.ServletException;
import org.apache.struts.actions.MappingDispatchAction;
import org.apache.struts.action.ActionForm;
import org.apache.struts.action.ActionForward;
import org.apache.struts.action.ActionMapping;
public class MappingDispatch_Action extends MappingDispatchAction
{
public ActionForward add(
ActionMapping mapping,
ActionForm form,
HttpServletRequest request,
HttpServletResponse response) throws Exception{
System.out.println("You are in add function.");
return mapping.findForward("add");
}
public ActionForward edit(
ActionMapping mapping,
ActionForm form,
HttpServletRequest request,
HttpServletResponse response) throws Exception{
System.out.println("You are in edit function.");
return mapping.findForward("edit");
}
public ActionForward search(
ActionMapping mapping,
ActionForm form,
HttpServletRequest request,
HttpServletResponse response) throws Exception{
System.out.println("You are in search function");
return mapping.findForward("search");
}
public ActionForward save(
ActionMapping mapping,
ActionForm form,
HttpServletRequest request,
HttpServletResponse response) throws Exception{
System.out.println("You are in save function");
return mapping.findForward("save");
}
}
|
No need to Develop an ActionForm Class
Developing the Action Mapping in the struts-config.xml
Here, we need to create multiple independent actions for each method defined in
the action class. Note that the value specified with the parameter attribute
is used to delegate request to the required method of the MappingDispatch_Action Class.
<action path="/MappingDispatchAction"
type="roseindia.net.MappingDispatch_Action"
parameter="add"
input="/pages/MappingDispatchAction.jsp"
scope="request"
validate="false">
<forward name="add" path="/pages/MappingDispatchActionAdd.jsp" />
</action>
<action path="/MappingDispatchAction"
type="roseindia.net.MappingDispatch_Action"
parameter="edit"
input="/pages/MappingDispatchAction.jsp"
scope="request"
validate="false">
<forward name="edit" path="/pages/MappingDispatchActionEdit.jsp" />
</action>
<action path="/MappingDispatchAction"
type="roseindia.net.MappingDispatch_Action"
parameter="search"
input="/pages/MappingDispatchAction.jsp"
scope="request"
validate="false">
<forward name="search" path="/pages/MappingDispatchActionSearch.jsp"/>
</action>
<action path="/MappingDispatchAction"
type="roseindia.net.MappingDispatch_Action"
parameter="save"
input="/pages/MappingDispatchAction.jsp"
scope="request"
validate="false">
<forward name="save" path="/pages/MappingDispatchActionSave.jsp" />
</action>
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Developing jsp page
Code of the jsp (MappingDispatchAction.jsp) to delegate
requests to different jsp pages :
<%@ taglib uri="/WEB-INF/struts-bean.tld" prefix="bean"%>
<%@ taglib uri="/WEB-INF/struts-html.tld" prefix="html"%>
<html:html locale="true">
<HEAD>
<TITLE>Mapping Dispatch Action Example</TITLE>
<BODY>
<H3>Dispatch Action Example</H3>
<p><html:link page="/MappingDispatchAction.do?parameter=add">Call Add Section</html:link></p>
<p><html:link page="/MappingDispatchAction.do?parameter=edit">Call Edit Section</html:link></p>
<p><html:link page="/MappingDispatchAction.do?parameter=search">Call Search Section</html:link></p>
<p><html:link page="/MappingDispatchAction.do?parameter=save">Call Save Section</html:link></p>
</html:html>
|
Add the following line in the index.jsp to call the
form.
<li>
<html:link page="/pages/MappingDispatchAction.jsp">Struts File
Upload</html:link>
<br>
Example demonstrates how MappingDispatchAction class works.
</li>
Building and Testing the Example
To build and deploy the application go to Struts\Strutstutorial
directory and type ant on the command prompt. This will deploy the application.
Open the browser and navigate to the MappingDispatchAction.jsp
page. Your browser displays the following MappingDispatchAction page.
Selecting Call Add Section
displays the following MappingDispatchActionAdd.jsp page
Selecting Call Edit Section
displays the following MappingDispatchActionEdit.jsp
page
Selecting Call Search Section
displays the following MappingDispatchActionSearch.jsp
page
Selecting Call Save Section
displays the following MappingDispatchActionSave.jsp
page
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Current Comments
3 comments so far (post your own) View All Comments Latest 10 Comments:There is a wrong understanding of MappingDispatchAction. In struts-config.xml the action paths must be something like:
<action path="callAdd" parameter="add" .../>
MappingDispatchAction uses the parameter to map the action to the add-method in MappingDispatch_Action. So in the jsp the code is as follows:
<html:link page="/callAdd.do">Call Add Section</html:link>
The Benefit of MappingDispatchAction is, that every action maps to a method only one class, which is like DispatchAction, but the mapping is not done via the parameter attribute, but via the action.
This misunderstanding may come from wrong interpretaion of the parameter attribute. This attribute is a multipurpose parameter for the Action-implementation and does not mean an URL-parameter.
Greetings,
Martin
Posted by Martin Krueger on Friday, 10.19.07 @ 17:57pm | #34398
I could understand much difference between mapping and lookup dispatch action
Posted by debu on Thursday, 06.28.07 @ 18:04pm | #20330
I think this page has been updated lately, and i am not finding any difference of conents between DispatchAction and MappingDispatchAction tutorial. Both are exactly same. Rather the information provided previously was correct and more sensible.
In general tutorial provided by roseindia is quiet useful in all other sense.
Thanks
Posted by angelina on Tuesday, 05.15.07 @ 17:03pm | #15999