Struts FAQS1

Struts

Describe Jakarta Struts Framework

It implements Model-View-Controller pattern in the framework and it is an open source
code. It saves time in design and implementation of a web based
application due to this framework and pattern as I is highly robust,
scalable and reliable.

What are the components of Struts?

Struts is based on the MVC design pattern. Struts components can be categories into Model, View and Controller.

Model: Components like business logic / business processes and data are
the part of Model.

View: JSP, HTML etc. are part of View

Controller: Action Servlet of Struts is part of Controller components
which works as front controller to handle all the requests.

Describe is ActionServlet

ActionServlet provides the "controller" in the Model-View-Controller (MVC) design pattern for web applications that is commonly known as "Model 2". This nomenclature
originated with a description in the JavaServerPages Specification, version 0.92, and has persisted ever since (in the absence of a better name).Controller is responsible for handling all the requests.

What is an Action Class used for?
An Action is an adapter between the contents of an incoming HTTP request and the corresponding business logic that should be executed to process this request. The controller
(ActionServlet) will select an appropriate Action for each request,
create an instance (if necessary), and call the perform method.

Actions must be programmed in a thread-safe manner, because the
controller will share the same instance for multiple simultaneous
requests. In this means you should design with the following items in
mind:

• Instance and static variables MUST NOT be used to
store information related to the state of a particular request. They
MAY be used to share global resources across requests for the same
action.

• Access to other resources (JavaBeans, session
variables, etc.) MUST be synchronized if those resources require
protection. (Generally, however, resource classes should be designed to
provide their own protection where necessary.

When an Action instance is first created, the controller servlet will
call setServlet() with a non-null argument to identify the controller
servlet instance to which this Action is attached. When the controller
servlet is to be shut down (or restarted), the setServlet() method will
be called with a null argument, which can be used to clean up any
allocated resources in use by this Action.


What is ActionForm?

An ActionForm is a JavaBean optionally associated with one or more ActionMappings. Such a bean will have had its properties initialized from the corresponding request
parameters before the corresonding action's perform() method is called.

When the properties of this bean have been populated, but before the
perform() method of the action is called, this bean's validate() method
will be called, which gives the bean a chance to verify that the
properties submitted by the user are correct and valid. If this method
finds problems, it returns an error messages object that encapsulates
those problems, and the controller servlet will return control to the
corresponding input form. Otherwise, the validate() method returns
null(), indicating that everything is acceptable and the corresponding
Action's perform() method should be called.

This class must be subclassed in order to be instantiated. Subclasses
should provide property getter and setter methods for all of the bean
properties they wish to expose, plus override any of the public or
protected methods for which they wish to provide modified
functionality.


What is Struts Validator Framework?

Struts Framework provides the
functionality to validate the form data. It can be use to validate the
data on the users browser as well as on the server side. Struts
Framework emits the java scripts and it can be used validate the form
data on the client browser. Server side validation of form can be
accomplished by sub classing your From Bean with DynaValidatorForm
class.


What are the core classes of the Struts Framework?

Core classes of Struts Framework
are ActionForm, Action, ActionMapping, ActionForward, ActionServlet etc.


What are Tag Libraries provided with Struts?

Struts provides a number of tag libraries that helps to create view components easily. These tag libraries are:

a) Bean Tags: Bean Tags are used to access the beans and their
properties.

b) HTML Tags: HTML Tags provides tags for creating the view components
like forms, buttons, etc..

c) Logic Tags: Logic Tags provides presentation logics that eliminate
the need for scriptlets.

d) Nested Tags: Nested Tags helps to work with the nested context.

What are difference between ActionErrors and ActionMessage?

ActionMessage: A class that
encapsulates messages. Messages can be either global or they are
specific to a particular bean property.

Each individual message is described by an ActionMessage object, which
contains a message key (to be looked up in an appropriate message
resources database), and up to four placeholder arguments used for
parametric substitution in the resulting message.

ActionErrors: A class that encapsulates the error messages being
reported by the validate() method of an ActionForm. Validation errors
are either global to the entire ActionForm bean they are associated
with, or they are specific to a particular bean property (and,
therefore, a particular input field on the corresponding form).

How you will handle exceptions in Struts?
In Struts you can handle the exceptions in two ways:

a) Declarative Exception Handling: You can either define global
exception handling tags in your struts-config.xml or define the
exception handling tags within .. tag.

Example:

key="database.error.duplicate"
path="/UserExists.jsp"
type="mybank.account.DuplicateUserException"/>

b) Programmatic Exception Handling: Here you can use try{}catch{} block
to handle the exception.