Struts 2 Tutorial – One Stop Solution for Beginners

If you are looking for a Java framework that can help you in developing JEE web applications quickly and efficiently, then Struts 2 is the perfect solution for you. Struts 2 is an open-source framework that is heavily used in the market. Through this Struts 2 Tutorial, I will help you to get started with it along with practical implementations.

Below are the topics I will be discussing in this Struts tutorial:

• What is Struts 2?
• Struts 2 Features
• Architecture of Struts 2
• Environment Setup
• Fundamental Concepts
  • Configurations
  • Actions
  • Interceptors
  • Value Stack
  • OGNL
• Struts 2 Tutorial Demo

What is Struts?

In layman terms, Struts is a Java-based open-sourced framework that helps in developing web application in J2EE. It extends the Java Servlet API and promotes the Model, View, Controller (MVC) architecture.  This makes the web applications developed in standard technologies like JSP, JavaBeans, and XML, more maintainable, extensible, and flexible. 

The Struts Framework was initially developed by Craig McClanahan and was handed over to Apache Foundation in May 2000. Gradually, it captures the position of a top-level Apache project in 2005 and later on February 2007, it was replaced by Struts 2.

The Struts Framework was extensively based on the MVC(Model-View-Controller) design paradigm. Its main aim was to separate the Model from the View and the Controller in the application to reduce dependency and promote Separation of Concerns (SoC). In other words, it helped in separating the application logic that mainly communicates with the database from the HTML pages through which the user interacts with the application and the instance which helps in channeling information between Model and View.

Features of Struts 2

1. POJO Based forms and actions: Action classes in Struts are treated as the controller in the application. They are responsible for responding to a user action, executing business logic, and returning a result with the view that has to be rendered. It acts as Model class as well.
2. Improved Tags and Customization: Various types of tags have been introduced in Struts 2 like UI tags, control tags, Data tags, etc which aids in application development.
3. AJAX Functionality: Struts 2 supports ajax technology which is typically used for generating an asynchronous request. It makes the enhances the performance of the application by sending only the required field data to the server.
4. Easy Integration: It provides easy integration with other Web frameworks such as Spring, DWR, SiteMesh and Tiles.
5. Minimal Configurations: While using Struts 2 application, there are no overhead configurations required. It works with minimal configurations where most of the settings take the default values unless there is any deviation.
6. Integrate View Technologies: With Struts2, you can easily integrate with various view technologies such as XSLT, JSP, Freemarker, velocity, etc.
7. Theme and Templates: Struts 2 provides support to 3 types of themes:
   1. Xhtml
   2. Simple
   3. Css_xhtml

Here XHTML is the default theme for Struts 2 and is mainly used for common look and feel.

Now that you know what is Struts and its various features, lets now move ahead with the this Struts Tutorial article and learn about its architecture.

Architecture

As you can see in the above diagram, Struts uses high-level MVC architecture. Here the Struts2 dispatch servlet filter is used to implement the Controller while actions are used to implement the Model and the View is implemented by combining result types and results. In this architecture, the common thread, linking, and integration with other components is enabled by the value stack and OGNL. On top of this, configurations for the web applications along with actions, interceptors, results, etc also help in channeling a lot of information.

Now, let me explain the complete workflow during the life cycle of a request generated by the user. Below I have listed down the step by step workflow for your better understanding of how Struts work:

• It begins with the User request that is sent to the server for requesting for some resource.
• This request is then processed by the Filter Dispatcher to determine the appropriate Action.
• Further, properly configured interceptor functionalities are then applied to the request such as validation, file upload, etc.
• Once the selected Action is decided and it executed based on the requested operation.
• In case, any post-processing required, configured interceptors are invoked.
• In the end, the result is provided by the view and is returned to the user.

I hope this clears the workflow within a Struts application. Lets now see what all you need in your system to get started with Struts in the next section of this Struts 2 Tutorial

Environment Setup

Below I have listed down the basic necessities to get started with Struts 2:

• Java
  In case you don’t have Java installed on your system, you can refer to the Java Installation article.

• Tomcat
  If you don’t have Tomcat in your system, you can visit here for free download.

• IDE (preferably Eclipse)
  Finally, you need your Eclipse IDE for application development.

Once done, you are ready to get your feet wet with Struts. In the next section of this Struts 2 Tutorial, I will give you a brief on the fundamental concepts of Struts 2.

Fundamental Concepts

1. Configurations

In any, struts application there are two main configuration files:

2. struts.xml file: This file holds the information regarding the configuration which are modified as actions. It is mainly used for overriding the default settings in an application. This file is generally created within the WEB-INF/classes directory in any Struts project.
3. struts.properties file: This file provides a mechanism that can alter the behavior of the framework. Since a framework makes use of a number of properties you can change any of it as per your requirement.

2. Actions

Actions or Action Classes are the core concepts in any Struts 2 application, as they act as the controller in the MVC pattern. In other words, Action classes contain the business logic which helps in processing the data. Other than this, action class is also responsible for responding to a users request, executing business logic. It also helps the framework in determining and returning a result on the basis of the configuration file (struts.xml), back to the user for rendering the View page.

Stuts2 actions classes are not singleton in nature i.e one instance of this class will be created with each request. Thus they need not to be thread-safe and are simple and independent. This makes testing of these classes much easier.

An action file can be created in three ways, which are as follows:

• Simple Action Class
  Any concrete java class can be used as a Struts 2 action class but the only requirement is that the class must contain a execute() method with the String return type. Below is the code to create a simple Action Class:

package com.edureka.struts2.action;

public class DemoAction {
	public String execute(){
		return "Welcome!";
	}
}

• Implementing Action interface
  A Struts 2 Action class can also be created by implementing the  com.opensymphony.xwork2.Action interface. It contains a single method i.e execute() which must be implemented by the implementing class. By implementing this interface you can make use of several constants such as SUCCESS, ERROR, NONE, INPUT and LOGIN which can be used for the result pages.
  Below code shows an example for the same:

package com.edureka.struts2.action;

import com.opensymphony.xwork2.Action;

public class DemoAction implements Action{

	public String execute(){
		return SUCCESS;
	}
}

• Extending ActionSupport Class

Action classes in Struts 2 generally extend the Action Support class which is the default implementation of Action interface. It provides various imperative functionalities for the web application development such as data validation, action level message, action level error message, field-level error message and read resource bundled, etc.

Below is the implementation of the same:

package com.edureka.struts2.action;
import  com.opensymphony.xwork2.ActionSupport;

public class  DemoAction extends  ActionSupport 
{  
  @Override
  public  String execute() throws  Exception {
    return  SUCCESS;
  }
}

3. Interceptors

Interceptor act as one of the major pillars of the Struts 2 framework. It is nothing but an object which is invoked during the preprocessing and postprocessing of a request.  It helps in controlling and maintaining the smooth transition of request and response cycle.

The main advantage of using interceptors is that it is pluggable. What I mean is, in case you no longer have any use of a specific concern like validation, exception handling, logging, etc., you can easily remove it from the application without having to redeploy it. For this, all you need to do is delete the entry from the struts.xml file.

The Struts2 framework provides a comprehensive set of pre-defined interceptors and common interceptor stacks which I have listed in the below table:

4. Value Stack

ValueStack in Struts2 framework is the storage area where the entire application’s data is stored for processing a request. This data is held within the ActionContext objects which makes use of the ThreadLocal for retrieving the values specific to any specific client request thread.

5. OGNL

OGNL stands for Object-Graph Navigation Language. It is a powerful expression language much like JSP and is mostly used for the reference and manipulation of data present in the ValueStack. Moreover, it also aids in transferring and converting the type of data.

Similar to JSP, OGNL contains a root object within the application context. Thus, you can provide the reference of the default object using markup notation which in this case is denoted using pound symbol. Struts 2 framework implements OGNL by building an ActionContext map. Below I have listed down the components of the ActionContext map:

• Application
• Session
• Value stack
• Request
• Parameters
• Attributes

With this, you are through the basics of Struts 2. In the next section of this Struts 2 article lets directly jump into the code and implement all you have learned till now.

Struts 2 Tutorial Demo

Here I will be creating a simple application where you need to input your name and the application will welcome you. Below is the screenshot of the complete project structure:

As you can see, in this project we will be creating 5 files which are:

1. HelloWorld.java
2. index.jsp
3. welcome.jsp
4. web.xml
5. struts.xml

Note: Before you start this project make sure you already have Tomcat installed on your system.

STEP I: In your Eclipse, go to File > New > Dynamic Web Project. Enter the Project Name and click on New Runtime.

STEP II: Here you need to select the version of Apache Tomcat you have downloaded on your system and click on Next.

STEP III: Next, click on Browse and navigate to the directory where Tomcat dependencies have been saved. Once done click on Finish and proceed with the Project Creation.

STEP IV: Let’s now add the Struts jar files which will be required for the successful execution of this project. You can download the JARs from here. Once you are ready with the JAR files, copy the JARs and paste them under WebContent > WEB-INF > lib.

STEP V: Now that we are ready with all the configurations lets set up the code files, starting with HelloWorld.java. For this, right-click on the project > New > Class. Fill out package and class name and click on finish.

STEP VI: Type in the below code in the HelloWorld.java file.

package com.edureka;

public class HelloWorld {
	private String name;
	
	public String getName() {
		return name;
	}
	
	public void setName(String name) {
		this.name = name;
	}
	
	public String execute() {
		return "success";
	}

}

STEP VII: Next create a new index.jsp file under WebContent and type in the below code:

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

<s:form action="verify">
  <s:textfield name="name" label="Enter Username" />
  <s:submit value="Click" align="center" />
</s:form>

STEP VIII: Now, again create a new welcome.jsp file under WebContent and type in the below code:

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

Welcome: <s:property value = "name"/>

STEP IX: Now go to WebContent > WEB-INF and type in the below code in the web.xml file.

<?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns="http://java.sun.com/xml/ns/javaee" 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>Struts2Demo</display-name>
  <welcome-file-list>
    <welcome-file>index.html</welcome-file>
  </welcome-file-list>
  <filter>
  <filter-name>struts2</filter-name>
  <filter-class>org.apache.struts2.dispatcher.ng.filter.StrutsPrepareandExecuteFilter</filter-class>
  </filter>
  <filter-mapping>
  <filter-name>struts2</filter-name>
  <url-pattern>/*</url-pattern>
  </filter-mapping>
</web-app>

STEP X: Finally, under Java Resources > src, create struts.xml file

<?xml version="1.0" encoding="UTF-8" ?>  
<!DOCTYPE struts PUBLIC "-//Apache Software Foundation//DTD Struts Configuration 2.1//EN" "http://struts.apache.org/dtds/struts-2.1.dtd">  

<struts>
	<package name = "default" extends = "struts-default">
	<action name = "verify" class = "com.edureka.HelloWorld">
	<result name = "success">welcome.jsp</result>
	</action>
	</package>
</struts>

STEP XI: Now go to the index.jsp page and right-click on it. Select Run on Server to execute the application.

This brings us to the end of this article on Struts 2 Tutorial. If you want to know more about Java you can refer to our other Java Blogs.

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