Why Struts 2

The new version Struts 2.0 is a combination of the Sturts action framework and Webwork. According to the Struts 2.0.1 release announcement, some key features are:

* Simplified Design - Programming the abstract classes instead of interfaces is one of design problem of struts1 framework that has been resolved in the struts 2 framework. Most of the Struts 2 classes are based on interfaces and most of its core interfaces are HTTP independent. Struts 2 Action classes are framework independent and are simplified to look as simple POJOs. Framework components are tried to keep loosely coupled.

* Simplified Actions - Actions are simple POJOs. Any java class with execute() method can be used as an Action class. Even we don't need to implement interfaces always. Inversion of Control is introduced while developing the action classes. This make the actions to be neutral to the underlying framework .
* No more ActionForms - ActionForms feature is no more known to the struts2 framework. Simple JavaBean flavored actions are used to put properties directly. No need to use all String properties.
* Simplified testability - Struts 2 Actions are HTTP independent and framework neutral. This enables to test struts applications very easily without resorting to mock objects.
* Intelligent Defaults - Most configuration elements have a default value which can be set according to the need. Even there are xml-based default configuration files that can be overridden according to the need.
* Improved results - Unlike ActionForwards, Struts 2 Results provide flexibility to create multiple type of outputs and in actual it helps to prepare the response.
* Better Tag features - Struts 2 tags enables to add style sheet-driven markup capabilities, so that we can create consistent pages with less code. Struts 2 tags are more capable and result oriented. Struts 2 tag markup can be altered by changing an underlying stylesheet. Individual tag markup can be changed by editing a FreeMarker template. Both JSP and FreeMarker tags are fully supported.
* Annotations introduced : Applications in struts 2 can use Java 5 annotations as an alternative to XML and Java properties configuration. Annotations minimize the use of xml.
* Stateful Checkboxes - Struts 2 checkboxes do not require special handling for false values.
* QuickStart - Many changes can be made on the fly without restarting a web container.
* customizing controller - Struts 1 lets to customize the request processor per module, Struts 2 lets to customize the request handling per action, if desired.
* Easy Spring integration - Struts 2 Actions are Spring-aware. Just need to add Spring beans!
* Easy plugins - Struts 2 extensions can be added by dropping in a JAR. No manual configuration is required!
* AJAX support - The AJAX theme gives interactive applications a significant boost.
The framework provides a set of tags to help you ajaxify your applications, even on Dojo. The AJAX features include:


1. AJAX Client Side Validation
2. Remote form submission support (works with the submit tag as well)
3. An advanced div template that provides dynamic reloading of partial HTML
4. An advanced template that provides the ability to load and evaluate JavaScript remotely
5. An AJAX-only tabbed Panel implementation
6. A rich pub-sub event model
7. Interactive auto complete tag

Struts 2 Architecture

Struts and webwork has joined together to develop the Struts 2 Framework. Struts 2 Framework is very extensible and elegant for the development of enterprise web application of any size. In this section we are going to explain you the architecture of Struts 2 Framework.

Request Lifecycle in Struts 2 applications

1. User Sends request: User sends a request to the server for some resource.

2. FilterDispatcher determines the appropriate action: The FilterDispatcher looks at the request and then determines the appropriate Action.

3. Interceptors are applied: Interceptors configured for applying the common functionalities such as workflow, validation, file upload etc. are automatically applied to the request.

4. Execution of Action: Then the action method is executed to perform the database related operations like storing or retrieving data from the database.

5. Output rendering: Then the Result renders the output.

6. Return of Request: Then the request returns through the interceptors in the reverse order. The returning request allows us to perform the clean-up or additional processing.

7. Display the result to user: Finally the control is returned to the servlet container, which sends the output to the user browser.

Image: Struts 2 high level overview of request processing:



Struts 2 Architecture

Struts 2 is a very elegant and flexible front controller framework based on many standard technologies like Java Filters, Java Beans, ResourceBundles, XML etc.

For the Model, the framework can use any data access technologies like JDBC, EJB, Hibernate etc and for the View, the framework can be integrated with JSP, JTL, JSF, Jakarta Velocity Engine, Templates, PDF, XSLT etc.

Exception Handling:

The Struts 2 Framework allows us to define exception handlers and inceptors.

* Exception Handlers:
Exception handlers allows us to define the exception handling procedure on global and local basis. Framework catches the exception and then displays the page of our choice with appropriate message and exception details.

* Interceptors:
The Interceptors are used to specify the "request-processing lifecycle" for an action. Interceptors are configured to apply the common functionalities like workflow, validation etc.. to the request.

Struts 2 Architecture

The following diagram depicts the architecture of Struts 2 Framework and also shows the the initial request goes to the servlet container such as tomcat, which is then passed through standard filer chain.

Image: Struts 2 Architecture



The filter chain includes:

* Action ContextCleanUp filter:
The ActionContextCleanUp filter is optional and it is useful when integration has to be done with other technologies like SiteMash Plugin.

* FilterDispatcher:
Next the FilterDispatch is called, which in turn uses the ActionMapper to determine whether to invoke an Action or not. If the action is required to be invoked, the FilterDispatcher delegates the control to the ActionProxy.

* ActionProxy:
The ActionProxy takes help from Configuration Files manager, which is initialized from the struts.xml. Then the ActionProxy creates an ActionInvocation, which implements the command pattern. The ActionInvocation process invokes the Interceptors (if configured) and then invokes the action. The the ActionInvocation looks for proper result. Then the result is executed, which involves the rendering of JSP or templates.

Then the Interceptors are executed again in reverse order. Finally the response returns through the filters configured in web.xml file. If the ActionContextCleanUp filter is configured, the FilterDispatcher does not clean the ThreadLocal ActionContext. If the ActionContextCleanUp filter is not present then the FilterDispatcher will cleanup all the ThreadLocals present.

In this section we have learnt about the Architecture of Struts 2 Framework.

Struts 2 History

Apache Struts is an open-source framework that is used for developing Java web application. Originally developed by the programmer and author Craig R. McClanahan, this was later taken over by the Apache Software
Foundation in 2002. Struts have provided an excellent framework for developing application easily by organizing JSP and Servlet based on HTML formats and Java code. Strut1 with all standard Java technologies and packages of Jakarta assists to create an extensible development environment. However, with the growing demand of web application, Strut 1 does not stand firm and needs to be changed with demand. This leads to the creation of Strut2, which is more developer friendly with features like Ajax, rapid development and extensibility.

Struts is a well-organized framework based on MVC architecture. In Model-View-Controller Architecture, Model stands for the business or database code, View represents the page design code and the Controller for navigational code. All these together makes Struts an essential framework for building Java applications. But with the development of new and lightweight MVC based framworks like Spring, Stripes and Tapestry, it becomes necessary to modify the Struts framework. So, the team of Apache Struts and another J2EE framework, WebWork of OpenSymphony joined hand together to develop an advanced framework with all possible developing features that will make it developer and user friendly.

Strut2 contains the combined features of Struts Ti and WebWork 2 projects that advocates higher level application by using the architecture of WebWork2 with features including a plugin framework, a new API, Ajax tags etc. So the Struts communities and the WebWork team brought together several special features in WebWork2 to make it more advance in the Open Source world. Later the name of WebWork2 has changed to Struts2. Hence, Apache Strut 2 is a dynamic, extensible framework for a complete application development from building, deploying and maintaining.

WebWork is a framework for web-application development that has been included in Struts framework 2.0 release. It has some unique concepts and constructs like its compatibility of working within existing Web APIs in Java rather than trying to replace them completely. It has been built specifically taking into account the developer’s productivity and code simplicity. Furthermore it is completely context dependent that provides a wrapper around XWork. When working on web applications the web work provides a context that helps web developer in specific implementations.

While, XWork provides a mechanism that is used for configuration and factory implementation management. This mechanism is dependencies inject mechanism.like Ajax, rapid development and extensibility.

Struts 2 Features

The strut-2 framework is designed for the compilation of the entire development cycle including of building, developing and maintaining the whole application. It is very extensible as each class of the framework is based on an Interface and all the base classes are given an extra application and even you can add your own. The basic platform requirements are Servlet API 2.4, JSP API 2.0 and Java5.

Some of the general features of the current Apache Strut 2 framework are given below.

Architecture – First the web browser request a resource for which the Filter Dispatcher decides the suitable action. Then the Interceptors use the required functions and after that the Action method executes all the functions like storing and retrieving data from a database
. Then the result can be seen on the output of the browser in HTML, PDF, images or any other.


Tags - Tags in Strut 2 allow creating dynamic web applications with less number of coding. Not only these tags contain output data but also provide style sheet driven markup that in turn helps in creating pages with less code. Here the tags also support validation and localization of coding that in turn offer more utilization. The less number of codes also makes it easy to read and maintain.
MVC – The Model View Controller in Strut 2 framework acts as a coordinator between application’s model and web view. Its Controller and View components can come together with other technology to develop the model. The framework has its library and markup tags to present the data dynamically.

Configuration – Provides a deployment descriptor to initialize resources in XML format. The initialization takes place simply by scanning all the classes using Java packages or you can use an application configuration file to control the entire configuration. Its general-purpose defaults allow using struts directly Out of the box.

Configuration files are re-loadable that allows changes without restarting a web container.

Other Features:
• All framework classes are based on interfaces and core interfaces are independent from HTTP.
• Check boxes do not require any kind of special application for false values.
• Any class can be used as an action class and one can input properties by using any JavaBean directly to the action class.
• Strut 2 actions are Spring friendly and so easy to Spring integration.
• AJAX theme enables to make the application more dynamic.
• Portal and servlet deployment are easy due to automatic portlet support without altering code.
• The request handling in every action makes it easy to customize, when required.