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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.
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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.
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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.
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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.
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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.
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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.
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What are
the core classes of the Struts Framework? |
Core classes of Struts Framework are
ActionForm, Action, ActionMapping, ActionForward, ActionServlet
etc.
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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.
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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).
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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.
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