TUTORIAL PART 1 : INTRODUCTION TO STRUTS2
Apache Struts2 was originally known as WebWork 2. After working independently for several years, the WebWork and Struts communities joined forces to create Struts2. This new version of Struts is simpler to use and closer to how Struts was always meant to be.
Struts 2 is a pull-MVC framework. i.e. the data that is to be displayed to user has to be pulled from the Action.
Struts2 supports annotation based configurations which are easy to create and more intuitive. Action class in Struts 2 act as the model in the web application. Unlike Struts, Struts 2 Action class are plain POJO objects thus simplifying the testing of the code. Struts2 also comes with power APIs to configure Interceptors that reduce greatly the coupling in application. The view part of Struts 2 is highly configurable and it supports different result-types such as Velocity, FreeMarker, JSP
The
FilterDispatcher filter is called which consults the ActionMapper to determine whether an Action should be invoked.If ActionMapper finds an Action to be invoked, the FilterDispatcher delegates control to ActionProxy.
ActionProxy reads the configuration file such as struts.xml. ActionProxy creates an instance of ActionInvocation class and delegates the control.
ActionInvocation is responsible for command pattern implementation. It invokes the Interceptors one by one (if required) and then invoke the Action.
Once the Action returns, the ActionInvocation is responsible for looking up the proper result associated with the Action result code mapped in
struts.xml.The Interceptors are executed again in reverse order and the response is returned to the Filter (In most cases to
FilterDispatcher). And the result is then sent to the servlet container which in turns send it back to client.Comparison of Struts 1 and Struts 2
Let us see the basic difference between Struts 1 and 2 framework.Unlike Struts 1, Struts 2 does not need to implement Action class. The Action in Struts 2 is a POJO object. Thus making it easy to unit test the code.
Struts 1 Actions are singletons and must be thread-safe since there will only be one instance of a class to handle all requests for that Action. Struts 2 Action objects are instantiated for each request, so there are no thread-safety issues.
Struts 1 Actions have dependencies on the servlet API since the
HttpServletRequest and HttpServletResponse is passed to the execute method when an Action is invoked. Struts 2 Actions are not coupled to a container. Most often the servlet contexts are represented as simple Maps, allowing Actions to be tested in isolation.Struts 1 uses an ActionForm object to capture input. Like Actions, all ActionForms must extend a base class. Since other JavaBeans cannot be used as ActionForms, developers often create redundant classes to capture input. Struts 2 uses Action properties as input properties, eliminating the need for a second input object. Input properties may be rich object types which may have their own properties.
Struts 1 integrates with JSTL, so it uses the JSTL EL. The EL has basic object graph traversal, but relatively weak collection and indexed property support. Struts 2 can use JSTL, but the framework also supports a more powerful and flexible expression language called “Object Graph Notation Language” (OGNL).
Struts 1 uses the standard JSP mechanism for binding objects into the page context for access. Struts 2 uses a “ValueStack” technology so that the taglibs can access values without coupling your view to the object type it is rendering.
Struts 1 supports separate Request Processors (lifecycles) for each module, but all the Actions in the module must share the same lifecycle. Struts 2 supports creating different lifecycles on a per Action basis via Interceptor Stacks. Custom stacks can be created and used with different Actions, as needed.
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