Struts 2 – Architecture

Struts 2 – Architecture

From a high level, Struts2 is a pull-MVC (or MVC2) framework. The Model-ViewController pattern in Struts2 is implemented with the following five core components −

• Actions
• Interceptors
• Value Stack / OGNL
• Results / Result types
• View technologies

Struts 2 is slightly different from a traditional MVC framework, where the action takes the role of the model rather than the controller, although there is some overlap.

Request Life Cycle

Based on the above diagram, you can understand the work flow through user’s request life cycle in Struts 2 as follows −

• User sends a request to the server for requesting for some resource (i.e. pages).
• The Filter Dispatcher looks at the request and then determines the appropriate Action.
• Configured interceptor functionalities applies such as validation, file upload etc.
• Selected action is performed based on the requested operation.
• Again, configured interceptors are applied to do any post-processing if required.
• Finally, the result is prepared by the view and returns the result to the user.

Sturts2 Example

As we have already learnt from the Struts 2 architecture, when you click on a hyperlink or submit an HTML form in a Struts 2 web-application, the input is collected by the Controller which is sent to a Java class called Actions. After the Action is executed, a result selects a resource to render the response. The resource is generally a JSP, but it can also be a PDF file, an Excel spreadsheet, or a Java applet window.

Assuming that you already have built your development environment. Now, let us proceed for building our first Hello World Struts2 project. The aim of this project is to build a web application that collects the user’s name and displays “Hello World” followed by the user name.

We would have to create following four components for any Struts 2 project −

Now we are going to use Eclipse IDE, so that all the required components will be created under a Dynamic Web Project. Let us now start with creating Dynamic Web Project.

Create Action Class

Action class is the key to Struts 2 application and we implement most of the business logic in action class. So let us create a java file HelloWorldAction.java under Java Resources >src with a package name com.tutorialspoint.struts2 with the contents given below.

The Action class responds to a user action when user clicks a URL. One or more of the Action class’s methods are executed and a String result is returned. Based on the value of the result, a specific JSP page is rendered.

package com.ducatindia.struts2;

publicclassHelloWorld{
privateString name;

publicString execute()throwsException{
return"success";
}

publicStringgetName(){
return name;
}

publicvoidsetName(String name){
this.name = name;
}
}

This is a very simple class with one property called “name”. We have standard getters and setter methods for the “name” property and an execute method that returns the string “success”.

The Struts 2 framework will create an object of the HelloWorld class and call the executed method in response to a user’s action. You put your business logic inside this method which finally returns the String constant. In other words, for each URL, you would have to implement one action class and either you can use that class name directly as your action name or you can map to some other name using struts.xml file as shown below.

Create a View

We need a JSP to present the final message, this page will be called by Struts 2 framework when a predefined action will happen and this mapping will be defined in struts.xml file. So let us create the below jsp file HelloWorld.jsp in the WebContent folder in your eclipse project. To do this, right click on the WebContent folder in the project explorer and select New >JSP File.

package com.tutorialspoint.struts2;

publicclassHelloWorldAction{
privateString name;

publicString execute()throwsException{
return"success";
}

publicStringgetName(){
return name;
}

publicvoidsetName(String name){
this.name = name;
}
}

This is a very simple class with one property called “name”. We have standard getters and setter methods for the “name” property and an execute method that returns the string “success”.

The Struts 2 framework will create an object of the HelloWorldAction class and call the executed method in response to a user’s action. You put your business logic inside this method which finally returns the String constant. In other words, for each URL, you would have to implement one action class and either you can use that class name directly as your action name or you can map to some other name using struts.xml file as shown below.

Create a View

We need a JSP to present the final message, this page will be called by Struts 2 framework when a predefined action will happen and this mapping will be defined in struts.xml file. So let us create the below jsp file HelloWorld.jsp in the WebContent folder in your eclipse project. To do this, right click on the WebContent folder in the project explorer and select New >JSP File.

<%@ page contentType="text/html; charset = UTF-8" %>

<%@taglib prefix ="s"uri="/struts-tags" %>

< html>
< head>
< title>Hello World< /title>
< /head>

< body>
      Hello World, < s:propertyvalue="name"/>
< /body>
< /html>

The taglib directive tells the Servlet container that this page will be using the Struts 2 tags and that these tags will be preceded by s.

The s:property tag displays the value of action class property “name> which is returned by the method getName() of the HelloWorldAction class.

Create Main Page

We also need to create index.jsp in the WebContent folder. This file will serve as the initial action URL where a user can click to tell the Struts 2 framework to call a defined method of the HelloWorldAction class and render the HelloWorld.jsp view.

<%@ page language ="java"contentType="text/html; charset = ISO-8859-1"pageEncoding="ISO-8859-1"%>

<%@taglib prefix ="s"uri="/struts-tags"%>

< head>
< title>Hello World< /title>
< /head>

< body>
< h1>Hello World From Struts2< /h1>
< formaction="hello">
< labelfor="name">Please enter your name< /label>< br/>
< inputtype="text"name="name"/>
< inputtype="submit"value="Say Hello"/>
< /form>
< /body>
< /html>

The hello action defined in the above view file will be mapped to the HelloWorldAction class and its execute method using struts.xml file. When a user clicks on the Submit button it will cause the Struts 2 framework to run the execute method defined in the HelloWorldAction class and based on the returned value of the method, an appropriate view will be selected and rendered as a response.

Configuration Files

We need a mapping to tie the URL, the HelloWorldAction class (Model), and the HelloWorld.jsp (the view) together. The mapping tells the Struts 2 framework which class will respond to the user’s action (the URL), which method of that class will be executed, and what view to render based on the String result that method returns.

So let us create a file called struts.xml. Since Struts 2 requires struts.xml to be present in the classes folder. Hence, create struts.xml file under the WebContent/WEB-INF/classes folder. Eclipse does not create the “classes” folder by default, so you need to do this yourself. To do this, right click on the WEB-INF folder in the project explorer and select New > Folder. Your struts.xml should look like −

< ?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>
< constantname="struts.devMode"value="true"/>

< packagename="helloworld"extends="struts-default">
< actionname="hello"
class="com.tutorialspoint.struts2.HelloWorldAction"
method="execute">
< resultname="success">/HelloWorld.jsp< /result>
< /action>
< /package>
< /struts>

Few words which need to be understood regarding the above configuration file. Here, we set the constant struts.devMode to true, because we are working in development environment and we need to see some useful log messages. Then, we define a package called helloworld.

Creating a package is useful when you want to group your actions together. In our example, we named our action as “hello” which is corresponding to the URL /hello.action and is backed up by theHelloWorldAction.class. The execute method of HelloWorldAction.class is the method that is run when the URL /hello.action is invoked. If the outcome of the execute method returns “success”, then we take the user to HelloWorld.jsp.

Next step is to create a web.xml file which is an entry point for any request to Struts 2. The entry point of Struts2 application will be a filter defined in deployment descriptor (web.xml). Hence, we will define an entry of org.apache.struts2.dispatcher.FilterDispatcher class in web.xml. The web.xml file needs to be created under the WEB-INF folder under WebContent. Eclipse had already created a skeleton web.xml file for you when you created the project. So, lets just modify it as follows −

< ?xml version ="1.0"Encoding="UTF-8"?>
< web-appxmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xmlns="http://java.sun.com/xml/ns/javaee"
xmlns:web="http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd"
xsi:schemaLocation="http://java.sun.com/xml/ns/javaee
   http://java.sun.com/xml/ns/javaee/web-app_3_0.xsd"
id="WebApp_ID"version="3.0">

< display-name>Struts 2< /display-name>

< welcome-file-list>
< welcome-file>index.jsp< /welcome-file>
< /welcome-file-list>

< filter>
< filter-name>struts2< /filter-name>
< filter-class>
         org.apache.struts2.dispatcher.FilterDispatcher
< /filter-class>
< /filter>

< filter-mapping>
< filter-name>struts2< /filter-name>
< url-pattern>/*< /url-pattern>
< /filter-mapping>
< /web-app>

We have specified index.jsp to be our welcome file. Then we have configured the Struts2 filter to run on all urls (i.e, any url that match the pattern /*)

The taglib directive tells the Servlet container that this page will be using the Struts 2 tags and that these tags will be preceded by s.

The s:property tag displays the value of action class property “name> which is returned by the method getName() of the HelloWorldAction class.

Create Main Page

We also need to create index.jsp in the WebContent folder. This file will serve as the initial action URL where a user can click to tell the Struts 2 framework to call a defined method of the HelloWorldAction class and render the HelloWorld.jsp view.

<%@ page language ="java"contentType="text/html; charset = ISO-8859-1" pageEncoding="ISO-8859-1"%>

<%@taglib prefix ="s"uri="/struts-tags"%>

<%@taglib prefix ="s"uri="/struts-tags"%>
< !DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" 
"http://www.w3.org/TR/html4/loose.dtd">

< html>
< head>
< title>Hello World< /title>
< /head>

< body>
< h1>Hello World From Struts2< /h1>
< formaction="hello">
< labelfor="name">Please enter your name< /label>< br/>
< inputtype="text"name="name"/>
< inputtype="submit"value="Say Hello"/>
< /form>
< /body>
< /html>

The hello action defined in the above view file will be mapped to the HelloWorldAction class and its execute method using struts.xml file. When a user clicks on the Submit button it will cause the Struts 2 framework to run the execute method defined in the HelloWorldAction class and based on the returned value of the method, an appropriate view will be selected and rendered as a response.

Configuration Files

We need a mapping to tie the URL, the HelloWorldAction class (Model), and the HelloWorld.jsp (the view) together. The mapping tells the Struts 2 framework which class will respond to the user’s action (the URL), which method of that class will be executed, and what view to render based on the String result that method returns.

So let us create a file called struts.xml. Since Struts 2 requires struts.xml to be present in the classes folder. Hence, create struts.xml file under the WebContent/WEB-INF/classes folder. Eclipse does not create the “classes” folder by default, so you need to do this yourself. To do this, right click on the WEB-INF folder in the project explorer and select New > Folder. Your struts.xml should look like −

< ?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>
< constantname="struts.devMode"value="true"/>

< packagename="helloworld"extends="struts-default">
< actionname="hello"
class="com.ducatindia.struts2.HelloWorldAction"
method="execute">
< resultname="success">/HelloWorld.jsp< /result>
< /action>
< /package>
< /struts>

Few words which need to be understood regarding the above configuration file. Here, we set the constant struts.devMode to true, because we are working in development environment and we need to see some useful log messages. Then, we define a package called helloworld.

Creating a package is useful when you want to group your actions together. In our example, we named our action as “hello” which is corresponding to the URL /hello.action and is backed up by theHelloWorldAction.class. The execute method of HelloWorldAction.class is the method that is run when the URL /hello.action is invoked. If the outcome of the execute method returns “success”, then we take the user to HelloWorld.jsp.

Next step is to create a web.xml file which is an entry point for any request to Struts 2. The entry point of Struts2 application will be a filter defined in deployment descriptor (web.xml). Hence, we will define an entry of org.apache.struts2.dispatcher.FilterDispatcher class in web.xml. The web.xml file needs to be created under the WEB-INF folder under WebContent. Eclipse had already created a skeleton web.xml file for you when you created the project. So, lets just modify it as follows −

< ?xml version ="1.0"Encoding="UTF-8"?>
< web-appxmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xmlns="http://java.sun.com/xml/ns/javaee"
xmlns:web="http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd"
xsi:schemaLocation="http://java.sun.com/xml/ns/javaee
   http://java.sun.com/xml/ns/javaee/web-app_3_0.xsd"
id="WebApp_ID"version="3.0">

< display-name>Struts 2< /display-name>

< welcome-file-list>
< welcome-file>index.jsp< /welcome-file>
< /welcome-file-list>

< filter>
< filter-name>struts2< /filter-name>
< filter-class>
         org.apache.struts2.dispatcher.FilterDispatcher
< /filter-class>
< /filter>

< filter-mapping>
< filter-name>struts2< /filter-name>
< url-pattern>/*< /url-pattern>
< /filter-mapping>
< /web-app>

We have specified index.jsp to be our welcome file. Then we have configured the Struts2 filter to run on all urls (i.e, any url that match the pattern /*)

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