Tuesday, July 7, 2009

Integrate GWT into Struts 2 Application

Source of this tutorial: http://cwiki.apache.org/WW/struts-2-gwt.html

These tutorial will demonstrate how to call an Struts 2 action, using GWT to submit a form and use the returned data.

Write your action.

Example action:

"Hello.java"
package example;

import com.opensymphony.xwork2.Action;

public class Hello {
private String firstName;
private String lastName;

public String execute() {
return Action.SUCCESS;
}

public String getFirstName() {
return firstName;
}
public void setFirstName(String firstName) {
this.firstName = firstName;
}
public String getLastName() {
return lastName;
}
public void setLastName(String lastName) {
this.lastName = lastName;
}
}

Write the mapping for your action.

In this example the mapping is in struts.xml:

struts.xml

<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE struts PUBLIC
"-//Apache Software Foundation//DTD Struts Configuration 2.0//EN"
"http://struts.apache.org/dtds/struts-2.0.dtd">

<struts>

<package name="example" extends="struts-default">
<action name="Hello" class="example.Hello">
<result type="json" />
</action>

<action name="Main" class="com.opensymphony.xwork2.ActionSupport">
<result>org.apache.struts.gwt.Main/Main.jsp</result>
</action>
</package>

</struts>




The "Hello" action has a result of type "json", which will serialize the action object into a JSON

string. If "firstName" is set to "John" and "lastName" is set to "Galt", the output of the "Hello" action will be:

{
"firstName" : "John",
"lastName" : "Galt"
}

The "Main" action points to the "Main.jsp" page which is the page that uses GWT. The path of the result is "org.apache.struts.gwt.Main/Main.jsp". That means that the files generated by GWT must go under a folder named "org.apache.struts.gwt.Main" under the root of your application. See "Deployment structure" for more details.

Write "Main.jsp" page.

This is the page that is generated by GWT's "applicationCreator". It has been renamed to .jsp because we have modified it to be a jsp page, instead of a plain html page.

Main.jsp

<%@ taglib prefix="s" uri="/struts-tags" %>
<html>
<head>
<s:head theme="ajax" debug="true"/>
<meta name='gwt:module' content='org.apache.struts.gwt.Main/org.apache.struts.gwt.Main'>
</head>

<body>
<script language="javascript" src="${pageContext.request.contextPath}/org.apache.struts.gwt.Main/gwt.js"/>

<form id="form1">
<input type="text" name="firstName">
<br/>
<input type="text" name="lastName">
<span id="slot1"></span>
</form>

<br/>
<span id="slot2"></span>
</body>
</html>

We set head's tag attribute "theme" to ajax to use Dojo, don't panic, you won't have to use it directly. Note that we have changed a few things from the original html page generated by GWT, we set "content" to "org.apache.struts.gwt.Main/org.apache.struts.gwt.Main" because the GWT generated files will be under "AppRoot/org.apache.struts.gwt.Main" instead of beneath root, and we set "src" to "${pageContext.request.contextPath}/org.apache.struts.gwt.Main/gwt.js" for the same reason. Without these two changes the GWT files wouldn't be loaded.
Struts2GWTHelper

This class will take care of making the request. Why? Why do I need this class? Couple of reasons, first, there is a bug on bug on HTTPRequest.asyncPost which doesn't encode the payload properly, second, if you want to submit a form, you have to encode it yourself, and this class will help you do that. Optionally you can download a jar containing this class (with more methods) from here, add this to your GWT application file (i.e Main.gwt.xml):

<inherits name='struts2gwt.Struts2GWT'/>

and add the jar to the classpath in your compile script (i.e Main-compile.cmd) and the compile script (i.e Main-shell.cmd).
Struts2GWTHelper .java

package org.apache.struts.gwt.client;

import com.google.gwt.user.client.ResponseTextHandler;

public class Struts2GWTHelper {

/**
* Make asynchronous post
* @param url Action url
* @param formId id of form that will be posted
* @param handler callback function
*/
public static native void asyncPost(String url, String formId, ResponseTextHandler handler) /*-{
dojo = $wnd.dojo;
//don't use the dojo.io.bind({...}) shortcut, it doesn't work here
var request = new dojo.io.Request(url);
request.load = function(type, data, request) {
handler.@com.google.gwt.user.client.ResponseTextHandler::onCompletion(Ljava/lang/String;)(data);
};
request.formNode = dojo.byId(formId);
request.method = "POST";
$wnd.dojo.io.bind(request);
}-*/;

/**
* Make asynchronous post
* @param url Action url
* @param handler callback function
*/
public static void asyncPost(String url, ResponseTextHandler handler) {
Struts2GWTHelper.asyncPost(url, handler);
}
}

See? It wasn't that bad.
Write your GWT entry point
Main.java

package org.apache.struts.gwt.client;

import com.google.gwt.core.client.EntryPoint;
import com.google.gwt.json.client.JSONObject;
import com.google.gwt.json.client.JSONParser;
import com.google.gwt.json.client.JSONString;
import com.google.gwt.user.client.ResponseTextHandler;
import com.google.gwt.user.client.ui.Button;
import com.google.gwt.user.client.ui.ClickListener;
import com.google.gwt.user.client.ui.Label;
import com.google.gwt.user.client.ui.RootPanel;
import com.google.gwt.user.client.ui.Widget;

/**
* Entry point classes define <code>onModuleLoad()</code>.
*/
public class Main implements EntryPoint {
final Label label = new Label();

/**
* This is the entry point method.
*/
public void onModuleLoad() {
final Button button = new Button("Click me");

button.addClickListener(new ClickListener() {
public void onClick(Widget sender) {
makeRequest();
}
});

RootPanel.get("slot1").add(button);
RootPanel.get("slot2").add(label);
}

private void makeRequest() {
Struts2GWTHelper.asyncPost("Hello.action", "form1", new ResponseTextHandler() {
public void onCompletion(String responseText) {
JSONObject obj = (JSONObject)JSONParser.parse(responseText);
JSONString firstName = (JSONString)obj.get("firstName");
JSONString lastName = (JSONString)obj.get("lastName");
label.setText("Welcome " + firstName.stringValue() + " " + lastName.stringValue());
}
});
}
}

The makeRequest() method will make a request to the "Hello" action that we created before, and will pass the fields of the form "form1" as parameters. Which will be populated on the action, and serialized back as JSON. Using JSONParser the JSON string is parsed into a JSON object. It is definitely not type safe as GWT Remoting, but it works.
Create Main.gwt.xml

Nothing new on this file, just as reference:
Main.gwt.xml

<module>

<!-- Inherit the core Web Toolkit stuff. -->
<inherits name='com.google.gwt.user.User'/>
<inherits name='com.google.gwt.json.JSON'/>

<!-- Specify the app entry point class. -->
<entry-point class='org.apache.struts.gwt.client.Main'/>

</module>

Deployment structure
Folder Notes
AppRoot The application deployment folder
AppRoot/index.html Welcome Page
AppRoot/org.apache.struts.gwt.Main Content generated by GWT (usually it gets generated into a folder named 'www')
AppRoot/WEB-INF Regular webapp files and classes


3 comments:

Yavé said...

What version libraries are used there?

esteriana said...
This comment has been removed by the author.
esteriana said...

I am having problem with dojo...
Java error console says dojo is undefined...
I download dojo-release-1.5.0-src package but nothing to do..

Please can anyone help me? What file should i download in order to make dojo and dojo.io known by the project and work right.
Waiting for an answer..
thnx