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Struts Interview Questions

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The Apache Struts web framework is a free open-source solution for creating Java web applications.

Web applications differ from conventional websites in that web applications can create a dynamic response. Many websites deliver only static pages. A web application can interact with databases and business logic engines to customize a response.

Web applications based on JavaServer Pages sometimes commingle database code, page design code, and control flow code. In practice, we find that unless these concerns are separated, larger applications become difficult to maintain.

One way to separate concerns in a software application is to use a Model-View-Controller (MVC) architecture. The Model represents the business or database code, the View represents the page design code, and the Controller represents the navigational code. The Struts framework is designed to help developers create web applications that utilize a MVC architecture.

The framework provides three key components:

  • A "request" handler provided by the application developer that is mapped to a standard URI.
  • A "response" handler that transfers control to another resource which completes the response.
  • A tag library that helps developers create interactive form-based applications with server pages.

The main purpose of using MVC pattern is to decouple the GUI from the Data. It also gives the ability to provide multiple views for the same Data. MVC pattern separates objects into three important sections:-
Model: – This section is specially for maintaining data. It is actually where your business logic, querying database, database connection etc. is actually implemented.
Views: – Displaying all or some portion of data, or probably different view of data. View is responsible for look and feel, Sorting, formatting etc.
Controller: – They are event handling section which affects either the model or the view. Controller responds to the mouse or keyboard input to command model and view to change. Controllers are associated with views. User interaction triggers the events to change the model, which in turn calls some methods of model to update its state to notify other registered views to refresh their display.

Below are the folders from point of view of root folder.

META-INF: – This directory has the Meta information.

WEB-INF/classes: – This location has the actual JAVA classes.

WEB-INF/classes/ApplicationResources.properties:- Contains text which application can use. For instance error messages.

WEB-INF/lib/struts.jar:- Contains the Struts servlet, helper classes, taglib code etc.

WEB-INF/*.tld:- The Struts tag libraries.

WEB-INF/struts-config.xml:- A Struts configuration file.

WEB-INF/web.xml:- Configuration file for the servlet container

Index.jsp:- All JSP files come in the root directory as this one Index.jsp.

Feature

Struts 1

Struts 2

Action classes

Struts 1 requires Action classes to extend an abstract base class. A common problem in Struts 1 is programming to abstract classes instead of interfaces.

An Struts 2 Action mayimplement an Actioninterface, along with other interfaces to enable optional and custom services. Struts 2 provides a base ActionSupport class to implement commonly used interfaces. Albeit, the Action interface is not required. Any POJO object with a executesignature can be used as an Struts 2 Action object.

Threading Model

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. The singleton strategy places restrictions on what can be done with Struts 1 Actions and requires extra care to develop. Action resources must be thread-safe or synchronized.

Struts 2 Action objects are instantiated for each request, so there are no thread-safety issues. (In practice, servlet containers generate many throw-away objects per request, and one more object does not impose a performance penalty or impact garbage collection.)

Servlet Dependency

Struts 1 Actions have dependencies on the servlet API since the HttpServletRequest and HttpServletResponse is passed to the executemethod 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 2 Actions can still access the original request and response, if required. However, other architectural elements reduce or eliminate the need to access the HttpServetRequest or HttpServletResponse directly.

Testability

A major hurdle to testing Struts 1 Actions is that the executemethod exposes the Servlet API. A third-party extension, Struts TestCase, offers a set of mock object for Struts 1.

Struts 2 Actions can be tested by instantiating the Action, setting properties, and invoking methods. Dependency Injection support also makes testing simpler.

Harvesting Input

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. DynaBeans can used as an alternative to creating conventional ActionForm classes, but, here too, developers may be redescribing existing JavaBeans.

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. The Action properties can be accessed from the web page via the taglibs. Struts 2 also supports the ActionForm pattern, as well as POJO form objects and POJO Actions. Rich object types, including business or domain objects, can be used as input/output objects. The ModelDriven feature simplifies taglb references to POJO input objects.

Expression Language

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).

Binding values into views

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. The ValueStack strategy allows reuse of views across a range of types which may have the same property name but different property types.

Type Conversion

Struts 1 ActionForm properties are usually all Strings. Struts 1 uses Commons-Beanutils for type conversion. Converters are per-class, and not configurable per instance.

Struts 2 uses OGNL for type conversion. The framework includes converters for basic and common object types and primitives.

Validation

Struts 1 supports manual validation via a validatemethod on the ActionForm, or through an extension to the Commons Validator. Classes can have different validation contexts for the same class, but cannot chain to validations on sub-objects.

Struts 2 supports manual validation via the validatemethod and the XWork Validation framework. The Xwork Validation Framework supports chaining validation into sub-properties using the validations defined for the properties class type and the validation context.

Control Of Action Execution

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.

Interceptors in Struts2 are based on Intercepting Filters.

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