Anjaneya Tech: May 2013

Wednesday 29 May 2013

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 oforg.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 ActionForwardlike "add" in case of add() method , "edit" in case of edit() etc. Each ActionForward is defined in thestruts-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.

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>
<html:link page="/MappingDispatchAction.do?parameter=add">Call Add Section</html:link>
<html:link page="/MappingDispatchAction.do?parameter=edit">Call Edit Section</html:link>
<html:link page="/MappingDispatchAction.do?parameter=search">Call Search Section</html:link>
<html:link page="/MappingDispatchAction.do?parameter=save">Call Save Section</html:link>

</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>
 
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 theMappingDispatchAction.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

and etc...

STRUTS ACTION - AGGREGATING ACTIONS IN STRUTS

If you are a Struts developer then you might have experienced the pain of writing huge number of Action classes for your project. The latest version of struts provides classes using which you can aggregate a related set of actions into a single unified action. In this article we will see how to achieve this. Struts provides four important classes for this purpose. These classes are called as Dispatchers. The important Dispatchers that struts provides includes : DispatchAction, ActionDispatcher , LookupDispatchAction andMappingDispatchAction.

All these classes can be found in the package org.apache.struts.actions. Let us look in to each of these in detail. Our examples use the simple CRUD actions.

DispatchAction: In this type of aggregation, the action class must extend DispatchAction class as shown.

public final class CRUDDispatchAction extends DispatchAction {

public ActionForward create(ActionMapping mapping,
ActionForm form,
HttpServletRequest request,
HttpServletResponse response) throws Exception {
return (mapping.findForward("success"));
}
...

and the action mapping will be as

<action path="/crudDispatchAction" type="com.companyname.projname.CRUDDispatchAction" name="formName" scope="request" input=" homeDef" parameter="methodToCall">
<forward name="success" path="targetDefName"/>
</action>

in your jsp you can call this action as

<html:link action="crudDispatchAction?methodToCall=create">Create</html:link>
...

Observe that the above class extends DispatchAction and so you cannot use this method if your class already extends your (some) super class (eg., the class where the session is validated/invalidated). Here the user has to send a query string variable (methodToCall) to set the action name to call.

ActionDispatcher: This flavor of aggregation is same as DispatchAction except that we need not extend ActionDispatcher, so we can use this method even if our class extends a super class. The following code snippet shows this scenario.

public final class CRUDActionDispatcher extends Action {

protected ActionDispatcher dispatcher = new ActionDispatcher(this, ActionDispatcher.DEFAULT_FLAVOR);

public ActionForward execute(ActionMapping mapping,
ActionForm form,
HttpServletRequest request,
HttpServletResponse response) throws Exception {
return dispatcher.execute(mapping, form, request, response);
}

The DEFAULT_FLAVOR field suggests that the default parameter is "method" if none is specified as parameter in struts-config.xml (eg,. methodToCall).
ActionDispatcher flavor also needs methodToCall parameter to be set (using hidden variable or a query string) as in case of DispatchAction.

LookupDispatchAction: This type of aggregation is useful in situations where in you have multiple submit buttons in a single form. The class must extend LookupDispatchAction. However, the great thing about this type is that its java script free. That means, you need not set any hidden variables or pass query string however, you must use submit buttons as shown.

<html:submit property="submit"><bean:message key="button.create"/></html: submit >
<html:submit property="submit"><bean:message key="button.read"/></html: submit >
...
The example Action class will be as follows

public class CRUDLookUpDispatchAction extends LookupDispatchAction {

protected Map getKeyMethodMap() {
Map map = new HashMap();
map.put("button.create", "create");
?
return map;
}
public ActionForward create(ActionMapping mapping,
ActionForm form,
HttpServletRequest request,
HttpServletResponse response) throws Exception {
return (mapping.findForward("success"));
}
Observe the getKeyMethodMap() method. The submit button names are specified in a Map and their keys comes from MessageResources file. Struts picks up the name from this file and redirects it to the value specified in the Map. The calling code in jsp however has multiple submit buttons only differing in their names.

MappingDispatchAction: This aggregation extends MappingDispatchAction class. This is the most useful type among the four types available. But as seen in other cases, you can use this type only when your action does not extend any other action. The good thing about this type is that the action mappings can differ and so need not be the same as in all other cases. To illustrate this consider the below mappings.

<action path="/createMappingAction" type="com.bodhtree.CRUDMappingDispatchAction" scope="request" input="homeDef" parameter="create">
<forward name="success" path="targetDef"/>
</action>
<action path="/readMappingAction" type="com.bodhtree.CRUDMappingDispatchAction" name=" formName" scope="request" input="homeDef" parameter=" read">
<forward name="success" path="targetDef"/>
</action>

Notice that in the first action mapping, there is no form bean while in the second the bean name is specified. This means that the user has the flexibility to change the mapping according to his needs and hence not been contained to use a constant mapping for all the CRUD actions. Note that in all the other types of aggregations, we must use the same mapping for all the CRUD actions.

Conclusion: Each of these types has their own pros and cons. DispatchAction is the default type which uses java script and we must extend DispatchAction to use it, ActionDispatcher is same as DispathAction except that we do not extend any action , LookupDispatchAction gives the flexibility to use multiple submit buttons while MappingDispatchAction allows us to change the action mappings according to our need. So each one of these has a particular usage and which one to use depends on the user requirement.

PHP SimpleXML

What is SimpleXML?

SimpleXML is new in PHP 5. It is an easy way of getting an element's attributes and text, if you know the XML document's layout.
Compared to DOM or the Expat parser, SimpleXML just takes a few lines of code to read text data from an element.
SimpleXML converts the XML document into an object, like this:

Elements - Are converted to single attributes of the SimpleXMLElement object. When there's more than one element on one level, they're placed inside an array
Attributes - Are accessed using associative arrays, where an index corresponds to the attribute name
Element Data - Text data from elements are converted to strings. If an element has more than one text node, they will be arranged in the order they are found

SimpleXML is fast and easy to use when performing basic tasks like:

Reading XML files
Extracting data from XML strings
Editing text nodes or attributes

However, when dealing with advanced XML, like namespaces, you are better off using the Expat parser or the XML DOM.

Installation

As of PHP 5.0, the SimpleXML functions are part of the PHP core. There is no installation needed to use these functions.

Using SimpleXML

Below is an XML file:

<?xml version="1.0" encoding="ISO-8859-1"?>
<note>
<to>Tove</to>
<from>Jani</from>
<heading>Reminder</heading>
<body>Don't forget me this weekend!</body>
</note>

We want to output the element names and data from the XML file above.
Here's what to do:

Load the XML file
Get the name of the first element
Create a loop that will trigger on each child node, using the children() function
Output the element name and data for each child node

Example

<?php
$xml = simplexml_load_file("test.xml");

echo $xml->getName() . " ";

foreach($xml->children() as $child)
 {
 echo $child->getName() . ": " . $child . " ";
 }
?>

The output of the code above will be:

note
to: Tove
from: Jani
heading: Reminder
body: Don't forget me this weekend!