1.What
is MVC?
Model-View-Controller (MVC) is a design
pattern put together to help control change. MVC decouples interface from
business logic and data.
Model : The model contains
the core of the application's functionality. The model encapsulates the state
of the application. Sometimes the only functionality it contains is state. It
knows nothing about the view or controller.
View: The view provides the presentation of
the model. It is the look of the application. The view can access the
model getters, but it has no knowledge of the setters. In addition, it knows
nothing about the controller. The view should be notified when changes to the
model occur.
Controller:The controller reacts
to the user input. It creates and sets the model.
2.What is a framework?
A framework is made up of the
set of classes which allow us to use a library in a best possible way for a
specific requirement.
3.What is Struts
framework?
Struts framework is an
open-source framework for developing the web applications in Java EE, based on
MVC-2 architecture. It uses and extends the Java Servlet API. Struts is robust
architecture and can be used for the development of application of any size.
Struts framework makes it much easier to design scalable, reliable Web
applications with Java.
4.What are the
components of Struts?
Struts components can be
categorize into Model, View and Controller:
Model: Components like business logic
/business processes and data are the part of model.
View: HTML, JSP are the view components.
Controller: Action Servlet of Struts is part of
Controller components which works as front controller to handle all the
requests.
5.What are the core
classes of the Struts Framework?
Struts is a set of cooperating
classes, servlets, and JSP tags that make up a reusable MVC 2 design.
JavaBeans
components for managing application state and behavior.
Event-driven
development (via listeners as in traditional GUI development).
Pages
that represent MVC-style views; pages reference view roots via the JSF
component tree.
6.What is
ActionServlet?
ActionServlet is a simple
servlet which is the backbone of all Struts applications. It is the main
Controller component that handles client requests and determines which Action
will process each received request. It serves as an Action factory – creating
specific Action classes based on user’s request.
7.What is role of ActionServlet?
ActionServlet performs the role
of Controller:
Process
user requests
Determine
what the user is trying to achieve according to the request
Pull
data from the model (if necessary) to be given to the appropriate view,
Select
the proper view to respond to the user
Delegates
most of this grunt work to Action classes
Is
responsible for initialization and clean-up of resources
8.What is the ActionForm?
ActionForm is javabean which
represents the form inputs containing the request parameters from the View
referencing the Action bean.
9.What are the important methods of ActionForm?
The important methods of ActionForm are : validate() & reset().
10.Describe validate() and reset() methods ?
validate()
: Used to validate properties after they have been populated; Called before
FormBean is handed to Action. Returns a collection of ActionError as ActionErrors.
Following is the method signature for the validate()
method.
public ActionErrors validate(ActionMapping mapping,HttpServletRequest request)
reset(): reset() method
is called by Struts Framework with each request that uses the defined
ActionForm. The purpose of this method is to reset all of the ActionForm's data
members prior to the new request values being set.
11.What is ActionMapping?
Action mapping contains all the
deployment information for a particular Action bean. This class is to determine
where the results of the Action will be sent once its processing is complete.
12.How is the Action Mapping specified ?
We can specify the action mapping in the configuration
file called struts-config.xml. Struts framework creates ActionMapping object from <ActionMapping>
configuration element of struts-config.xml file
<action-mappings>
<action path="/submit"
type="submit.SubmitAction"
name="submitForm"
input="/submit.jsp"
scope="request"
validate="true">
<forward name="success" path="/success.jsp"/>
<forward name="failure" path="/error.jsp"/>
</action>
</action-mappings>
13.What is role of Action Class?
An Action Class performs a role
of an adapter between the contents of an incoming HTTP request and the
corresponding business logic that should be executed to process this request.
14.In which method of Action class the business logic is
executed ?
In the execute() method
of Action class the business logic is executed.
public ActionForward execute(
ActionMapping mapping,
ActionForm form,
HttpServletRequest request,
HttpServletResponse response)
throws Exception ;
execute() method of Action class:
Perform
the processing required to deal with this request
Update
the server-side objects (Scope variables) that will be used to create the next
page of the user interface
Return
an appropriate ActionForward object
15.What design patterns are used in Struts?
Struts is based on model 2 MVC (Model-View-Controller)
architecture. Struts controller uses the command design pattern and the
action classes use the adapter design pattern. The process() method of the RequestProcessor uses the template
method design pattern. Struts also implement the following J2EE design
patterns.
Service
to Worker
Dispatcher
View
Composite
View (Struts Tiles)
Front
Controller
View
Helper
Synchronizer
Token
16.Can
we have more than one struts-config.xml file for a single Struts application?
Yes, we can have more than one
struts-config.xml for a single Struts application. They can be configured as
follows:
<servlet>
<servlet-name>action</servlet-name>
<servlet-class>
org.apache.struts.action.ActionServlet
</servlet-class>
<init-param>
<param-name>config</param-name>
<param-value>
/WEB-INF/struts-config.xml,
/WEB-INF/struts-admin.xml,
/WEB-INF/struts-config-forms.xml
</param-value>
</init-param>
.....
<servlet>
17.What is the directory structure of
Struts application?
The directory structure of Struts
application :
18.What is the difference between
session scope and request scope when saving formbean ?
when the scope is request,the
values of formbean would be available for the current request.
when the scope is session,the values of formbean would be available
throughout the session.
19.What
are the important tags of struts-config.xml ?
The five important sections are:
20.What are the different kinds of
actions in Struts?
The different kinds of actions in
Struts are:
ForwardAction
IncludeAction
DispatchAction
LookupDispatchAction
SwitchAction
21.What
is DispatchAction?
The DispatchAction class is used to
group related actions into one class. Using this class, you can have a method
for each logical action compared than a single execute method. The
DispatchAction dispatches to one of the logical actions represented by the
methods. It picks a method to invoke based on an incoming request parameter.
The value of the incoming parameter is the name of the method that the
DispatchAction will invoke.
22.How to use DispatchAction?
To use the DispatchAction, follow these
steps :
Create
a class that extends DispatchAction (instead of Action)
In
a new class, add a method for every function you need to perform on the service
– The method has the same signature as the execute() method of an Action class.
Do
not override execute() method – Because
DispatchAction class itself provides execute() method.
Add
an entry to struts-config.xml
23.What is the use of
ForwardAction?
The ForwardAction
class is useful when you’re trying to integrate Struts into an existing
application that uses Servlets to perform business logic functions. You can use
this class to take advantage of the Struts controller and its functionality,
without having to rewrite the existing Servlets. Use ForwardAction to forward a request to another resource in your
application, such as a Servlet that already does business logic processing or
even another JSP page. By using this predefined action, you don’t have to write
your own Action class. You just have to set up the struts-config file properly to use ForwardAction.
24.What is IncludeAction?
The IncludeAction
class is useful when you want to integrate Struts into an application that uses
Servlets. Use the IncludeAction class to include another resource in the
response to the request being processed.
25.What is the difference between ForwardAction and
IncludeAction?
The difference is that you need to use the IncludeAction only if the action is going to be included by another
action or jsp. Use ForwardAction to forward a request to another resource in your
application, such as a Servlet that already does business logic processing or
even another JSP page.
26.What is LookupDispatchAction?
The LookupDispatchAction
is a subclass of DispatchAction. It does a reverse lookup on the resource bundle to
get the key and then gets the method whose name is associated with the key into
the Resource Bundle.
27.What is the use of LookupDispatchAction?
LookupDispatchAction is useful
if the method name in the Action is not driven by its name in the front end,
but by the Locale independent key into the resource bundle. Since the key is
always the same, the LookupDispatchAction shields your application from the
side effects of I18N.
28.What is difference
between LookupDispatchAction and DispatchAction?
The difference between
LookupDispatchAction and DispatchAction is that the actual method that gets
called in LookupDispatchAction is based on a lookup of a key value instead of
specifying the method name directly.
29.What is SwitchAction?
The SwitchAction class provides
a means to switch from a resource in one module to another resource in a
different module. SwitchAction is useful only if you have multiple modules in
your Struts application. The SwitchAction class can be used as is, without
extending.
30.What if <action> element has <forward> declaration with
same name as global forward?
In this case the global forward is not used. Instead
the <action> element’s <forward>
takes precendence.
31.What is
DynaActionForm?
A specialized subclass of ActionForm that allows the creation of form beans with dynamic
sets of properties (configured in configuration file), without requiring the
developer to create a Java class for each type of form bean.
32.What are the steps need to use DynaActionForm?
Using a DynaActionForm
instead of a custom subclass of ActionForm is relatively straightforward. You
need to make changes in two places:
In
struts-config.xml: change your <form-bean> to be an org.apache.struts.action.DynaActionForm instead of
some subclass of ActionForm
<form-bean name="loginForm"type="org.apache.struts.action.DynaActionForm" >
<form-property name="userName" type="java.lang.String"/>
<form-property name="password" type="java.lang.String" />
</form-bean>
In
your Action subclass that
uses your form bean:
o
import
org.apache.struts.action.DynaActionForm
o
downcast
the ActionForm parameter in execute() to a DynaActionForm
o
access
the form fields with get(field) rather than getField()
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import org.apache.struts.action.Action;
import org.apache.struts.action.ActionForm;
import org.apache.struts.action.ActionForward;
import org.apache.struts.action.ActionMapping;
import org.apache.struts.action.ActionMessage;
import org.apache.struts.action.ActionMessages;
import org.apache.struts.action.DynaActionForm;
public class DynaActionFormExample extends Action {
public ActionForward execute(ActionMapping mapping, ActionForm form,
HttpServletRequest request, HttpServletResponse response)
throws Exception {
DynaActionForm loginForm = (DynaActionForm) form;
ActionMessages errors = new ActionMessages();
if (((String) loginForm.get("userName")).equals("")) {
errors.add("userName", new ActionMessage(
"error.userName.required"));
}
if (((String) loginForm.get("password")).equals("")) {
errors.add("password", new ActionMessage(
"error.password.required"));
}
...........
33.How to display validation errors on jsp page?
<html:errors/> tag displays all the errors. <html:errors/> iterates over ActionErrors request attribute.
34.What are the various Struts tag libraries?
The various Struts tag
libraries are:
HTML
Tags
Bean
Tags
Logic
Tags
Template
Tags
Nested
Tags
Tiles
Tags
35.What is the use of
<logic:iterate>?
<logic:iterate> repeats the nested body content of this tag over a
specified collection.
<table border=1>
<logic:iterate id="customer" name="customers">
<tr>
<td><bean:write name="customer" property="firstName"/></td>
<td><bean:write name="customer" property="lastName"/></td>
<td><bean:write name="customer" property="address"/></td>
</tr>
</logic:iterate>
</table>
36.What are differences between <bean:message> and
<bean:write>
<bean:message>: is used to retrive keyed values from resource
bundle. It also supports the ability to include parameters that can be
substituted for defined placeholders in the retrieved string.
<bean:message key="prompt.customer.firstname"/>
<bean:write>: is used to retrieve and print the value of the bean
property. <bean:write> has no body.
<bean:write name="customer" property="firstName"/>
37.How the exceptions are handled in struts?
Exceptions in Struts are
handled in two ways:
Programmatic exception handling : Explicit
try/catch blocks in any code that can throw exception. It works well when
custom value (i.e., of variable) needed when error occurs.
Declarative exception handling :You can
either define <global-exceptions> handling tags
in your struts-config.xml or define the
exception handling tags within <action></action> tag. It works
well when custom page needed when error occurs. This approach applies only to
exceptions thrown by Actions.
<global-exceptions>
<exception key="some.key"
type="java.lang.NullPointerException"
path="/WEB-INF/errors/null.jsp"/>
</global-exceptions>
or
<exception key="some.key"
type="package.SomeException"
path="/WEB-INF/somepage.jsp"/>
38.What is difference
between ActionForm and DynaActionForm?
An
ActionForm represents an
HTML form that the user interacts with over one or more pages. You will provide
properties to hold the state of the form with getters and setters to access
them. Whereas, using DynaActionForm there is no
need of providing properties to hold the state. Instead these properties and
their type are declared in the struts-config.xml
The
DynaActionForm bloats up the
Struts config file with the xml based definition. This gets annoying as the
Struts Config file grow larger.
The
DynaActionForm is not
strongly typed as the ActionForm. This means there is no compile time checking
for the form fields. Detecting them at runtime is painful and makes you go
through redeployment.
ActionForm
can be cleanly organized in packages as against the flat organization in the
Struts Config file.
ActionForm
were designed to act as a Firewall between HTTP and the Action classes, i.e.
isolate and encapsulate the HTTP request parameters from direct use in Actions.
With DynaActionForm, the property
access is no different than using request.getParameter( .. ).
DynaActionForm construction
at runtime requires a lot of Java Reflection (Introspection) machinery that can
be avoided.
39.How can we make message resources definitions file
available to the Struts framework environment?
We can make message resources definitions file
(properties file) available to Struts framework environment by adding this file
to struts-config.xml.
40.What
is the life cycle of ActionForm?
The lifecycle of ActionForm invoked by the RequestProcessor is as follows:
Retrieve
or Create Form Bean associated with Action
"Store"
FormBean in appropriate scope (request or session)
Reset
the properties of the FormBean
Populate
the properties of the FormBean
Validate
the properties of the FormBean
Pass
FormBean to Action