Java Practical info : The Struts Configuration fileStruts Architecture

FormBean's and Validation

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<span style="font-family: "Georgia","serif"; font-size: 12.0pt; line-height: 115%;">In this post , you will learn
what form beans is, what its importance is, how to use form beans in struts
application, and then the validation mechanisms to validate the struts form
fields like programmatic and declarative, validation at server side and cliet
side. First we will start with what form beans is and what is its importance,
the following section describes what form beans is.<o:p></o:p></span></div>
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<b><span style="font-family: "Georgia","serif"; font-size: 12.0pt; line-height: 115%;">Form
Bean<o:p></o:p></span></b></div>
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<b><span style="font-family: "Georgia","serif"; font-size: 12.0pt; line-height: 115%;"><br></span></b></div>
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<span style="font-family: "Georgia","serif"; font-size: 12.0pt; line-height: 115%;">Form Bean in struts framework
is a simple java bean class that is a subtype of
org.apache.struts.action.ActionForm class. Form Beans provides a proper
mechanism to exchange the data between the view and actions with reduced
dependency i.e this serves as a transfer object pattern some times known as
Data Transfer Object(DTO). A part from this form beans separates the form data
conversions and validations from actions, which reduces the complexity of the
actions and provides a proper responsibility division. Note: It is not
recommended to use form beans as a Transfer Object for transferring the data
between the controller and Model since form beans are dependent on struts API
and it is not better practice to increase dependency in such a way.<o:p></o:p></span></div>
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<b><span style="font-family: "Georgia","serif"; font-size: 12.0pt; line-height: 115%;">Need of
Form Beans<o:p></o:p></span></b></div>
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<span style="font-family: "Georgia","serif"; font-size: 12.0pt; line-height: 115%;">Most of the Actions designed in
struts applications are required to process the form data and in all such an
actions if we try to obtain form data using getParameter() method of
ServletRequest, we will face the following problems<o:p></o:p></span></div>
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<span style="font-family: Wingdings; font-size: 12.0pt; line-height: 115%; mso-bidi-font-family: Wingdings; mso-fareast-font-family: Wingdings;"> Ø<span style="font-family: 'Times New Roman'; font-size: 7pt; line-height: normal;">  </span></span><span style="font-family: "Georgia","serif"; font-size: 12.0pt; line-height: 115%;">Dependency
between the view & actions increases<o:p></o:p></span></div>
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<span style="font-family: Wingdings; font-size: 12.0pt; line-height: 115%; mso-bidi-font-family: Wingdings; mso-fareast-font-family: Wingdings;"> Ø<span style="font-family: 'Times New Roman'; font-size: 7pt; line-height: normal;">  </span></span><span style="font-family: "Georgia","serif"; font-size: 12.0pt; line-height: 115%;">Data
conversions has to be performed from actions , which increases the complexity
of the action classes, affects the understandability of the action classes and
if the same conversions are required with different forms data then either
we  need to implement them independently
or need to develop out own library.<o:p></o:p></span></div>
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<span style="font-family: Wingdings; font-size: 12.0pt; line-height: 115%; mso-bidi-font-family: Wingdings; mso-fareast-font-family: Wingdings;"> Ø<span style="font-family: 'Times New Roman'; font-size: 7pt; line-height: normal;">  </span></span><span style="font-family: "Georgia","serif"; font-size: 12.0pt; line-height: 115%;">Affects
the productivity<o:p></o:p></span></div>
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<span style="font-family: Wingdings; font-size: 12.0pt; line-height: 115%; mso-bidi-font-family: Wingdings; mso-fareast-font-family: Wingdings;"> Ø<span style="font-family: 'Times New Roman'; font-size: 7pt; line-height: normal;">  </span></span><span style="font-family: "Georgia","serif"; font-size: 12.0pt; line-height: 115%;">If any
validations are required for the form fields , they have to be performed in
action class, which once again increases the complexity<o:p></o:p></span></div>
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<b><span style="font-family: "Georgia","serif"; font-size: 12.0pt; line-height: 115%;">Benefits
of Form Beans<o:p></o:p></span></b></div>
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<b><span style="font-family: "Georgia","serif"; font-size: 12.0pt; line-height: 115%;"><br></span></b></div>
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<span style="font-family: Wingdings; font-size: 12.0pt; line-height: 115%; mso-bidi-font-family: Wingdings; mso-fareast-font-family: Wingdings;"> Ø<span style="font-family: 'Times New Roman'; font-size: 7pt; line-height: normal;">  </span></span><span style="font-family: "Georgia","serif"; font-size: 12.0pt; line-height: 115%;">Form
Beans provides the following benefits:<o:p></o:p></span></div>
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<span style="font-family: Wingdings; font-size: 12.0pt; line-height: 115%; mso-bidi-font-family: Wingdings; mso-fareast-font-family: Wingdings;"> Ø<span style="font-family: 'Times New Roman'; font-size: 7pt; line-height: normal;">  </span></span><span style="font-family: "Georgia","serif"; font-size: 12.0pt; line-height: 115%;">Separates
the form data conversions and validations from actions<o:p></o:p></span></div>
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<span style="font-family: Wingdings; font-size: 12.0pt; line-height: 115%; mso-bidi-font-family: Wingdings; mso-fareast-font-family: Wingdings;"> Ø<span style="font-family: 'Times New Roman'; font-size: 7pt; line-height: normal;">  </span></span><span style="font-family: "Georgia","serif"; font-size: 12.0pt; line-height: 115%;">Serves
as a transfer object  between the view
and controller i.e this follows Transfer Object pattern some times known as
Data Transfer Object(DTO)<o:p></o:p></span></div>
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<b><span style="font-family: "Georgia","serif"; font-size: 12.0pt; line-height: 115%;"> </span></b><b><span style="font-family: "Georgia","serif"; font-size: 12.0pt; line-height: 115%;"> </span></b></div>
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<b><span style="font-family: "Georgia","serif"; font-size: 12.0pt; line-height: 115%;">Using
Form bean in Struts application:<o:p></o:p></span></b></div>
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<span style="font-family: "Georgia","serif"; font-size: 12.0pt; line-height: 115%;">Using form beans in struts
application is a simple two-step operation, first write a form bean class and
then configure the form bean to work with the struts application, the following
section describes about these two operation in detail.<o:p></o:p></span></div>
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<b><span style="font-family: "Georgia","serif"; font-size: 12.0pt; line-height: 115%;">Writing
a Struts Form bean class<o:p></o:p></span></b></div>
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<span style="font-family: "Georgia","serif"; font-size: 12.0pt; line-height: 115%;">The regular form bean class is a java class that satisfies
the following rules:<o:p></o:p></span></div>
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<span style="font-family: "Georgia","serif"; font-size: 12.0pt; line-height: 115%;"><br></span></div>
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<span style="font-family: Wingdings; font-size: 12.0pt; line-height: 115%; mso-bidi-font-family: Wingdings; mso-fareast-font-family: Wingdings;"> Ø<span style="font-family: 'Times New Roman'; font-size: 7pt; line-height: normal;">  </span></span><span style="font-family: "Georgia","serif"; font-size: 12.0pt; line-height: 115%;">The
form bean class should be a public non-abstract class<o:p></o:p></span></div>
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<span style="font-family: Wingdings; font-size: 12.0pt; line-height: 115%; mso-bidi-font-family: Wingdings; mso-fareast-font-family: Wingdings;"> Ø<span style="font-family: 'Times New Roman'; font-size: 7pt; line-height: normal;">  </span></span><span style="font-family: "Georgia","serif"; font-size: 12.0pt; line-height: 115%;">The
form bean class should be a subtype of org.apache.struts.action.ActionForm<o:p></o:p></span></div>
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<span style="font-family: Wingdings; font-size: 12.0pt; line-height: 115%; mso-bidi-font-family: Wingdings; mso-fareast-font-family: Wingdings;"> Ø<span style="font-family: 'Times New Roman'; font-size: 7pt; line-height: normal;">  </span></span><span style="font-family: "Georgia","serif"; font-size: 12.0pt; line-height: 115%;">Form
bean class should have no-argument constructor ,we are allowed to have multiple
constructors as per our applications requirement<o:p></o:p></span></div>
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<span style="font-family: Wingdings; font-size: 12.0pt; line-height: 115%; mso-bidi-font-family: Wingdings; mso-fareast-font-family: Wingdings;"> Ø<span style="font-family: 'Times New Roman'; font-size: 7pt; line-height: normal;">  </span></span><span style="font-family: "Georgia","serif"; font-size: 12.0pt; line-height: 115%;">The
form bean class should have a set and get method for each of the property that
it has to represented, where these set and get methods should be public as
written according to the java bean standards.<o:p></o:p></span></div>
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<span style="font-family: Wingdings; font-size: 12.0pt; line-height: 115%; mso-bidi-font-family: Wingdings; mso-fareast-font-family: Wingdings;"> Ø<span style="font-family: 'Times New Roman'; font-size: 7pt; line-height: normal;">  </span></span><span style="font-family: "Georgia","serif"; font-size: 12.0pt; line-height: 115%;">The
form bean class can optionally override reset()and validate() methods of Action
Form, you will learn more about reset() and validate() methods in detail in the
next post.<o:p></o:p></span></div>
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<span style="font-family: "Georgia","serif"; font-size: 12.0pt; line-height: 115%;">The following code snippet shows a regular form bean class
that is designed to represent a login form with two properties, uname of type
java.lang.String and pass of type java.lang.String.<o:p></o:p></span></div>
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FormBean's and Validation

In this post , you will learn what form beans is, what its importance is, how to use form beans in struts application, and then the valid...

The Action Class

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<span style="font-family: "Georgia","serif"; font-size: 12.0pt; line-height: 115%;">The action class is a class
that is a subtype of org.apache.struts.action.Action. The action class that is
a part of controller provdes an entry point where we can start with our
application code to process the request. As shown in the architecture RequestProcessor
invokes the action by invoking the execute() method of the action , where the
action takes the responsibility to communicate with the model components and
prepare the data for the view that is required to prepare presentation. We need
to the view that is required to prepare presentation. We need to configure the
action I the struts configuration file using <action> tag configure the
action in the struts configuration file using <action> tag and map it to
a unique path so that the RequestProcessor can dispatch the request to our
action when a client makes a request with the specified path the following
snippet shows the mapping configuration in struts configuration file.<o:p></o:p></span></div>
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Code Snippet</div>
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<action path=”/login”</div>
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                Type=”com.chandra.struts.LoginAction”/></div>
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<br></div>
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<span style="font-family: "Georgia","serif"; font-size: 12.0pt; line-height: 115%;">Now as we know the basic
elements of the struts architecture we will now start with a first simple
struts application that can explain about the basic configurations and as we
move on we will learn the other elements of the struts architecture like form
beans , exception handlers, plugins etc., The following post explains a basic
struts example.<o:p></o:p></span></div>
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<b><span style="font-family: "Georgia","serif"; font-size: 12.0pt; line-height: 115%;">Writing
your first Struts Application<o:p></o:p></span></b></div>
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<b><span style="font-family: "Georgia","serif"; font-size: 12.0pt; line-height: 115%;"><br></span></b></div>
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<span style="font-family: "Georgia","serif"; font-size: 12.0pt; line-height: 115%;">Here to make the first example
simple we are implementing a login process which is a well known process, this
example consists of a Login.html which provides an entry point for this
application by providing login view allowing the user to make a login action,
the Login.html is shown in the following listing.<o:p></o:p></span></div>
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<span style="font-family: "Georgia","serif"; font-size: 12.0pt; line-height: 115%;"><br></span></div>
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<b>Login.html<o:p></o:p></b></div>
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<b><br></b></div>
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<html></div>
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 <body></div>
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   <form action=”login.do”><pre></div>
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  User Name :
<input type=”text” name=”uname”/></div>
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 Password  : <Input type=”password” name =”pass”/></div>
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</pre></form></div>
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</body></div>
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</html></div>
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<span style="font-family: "Georgia","serif"; font-size: 12.0pt; line-height: 115%;">The request make using the
Login.html is recived by the ActionServlet which then dispatches the request to
the RequestProcessor. The RequestProcessor after some request processing tasks
it invokes the execute method on the action class object, the LoaginAction
class to process the login request is shown in the following <o:p></o:p></span></div>
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<b><span style="font-family: "Georgia","serif"; font-size: 12.0pt; line-height: 115%;">LoginAction.java<o:p></o:p></span></b></div>
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<b><span style="font-family: "Georgia","serif"; font-size: 12.0pt; line-height: 115%;"><br></span></b></div>
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Package com.chandra.struts;</div>
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Import org.apache.struts.action.*;</div>
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Import javax.servlet.http.*;</div>
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/**</div>
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<span style="font-family: Symbol; mso-bidi-font-family: Symbol; mso-fareast-font-family: Symbol;">·<span style="font-family: 'Times New Roman'; font-size: 7pt;">        
</span></span>@author Chandra</div>
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*/</div>
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Public class LoginAction extends Action{</div>
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                Public  ActionFrward execute(ActionMapping
am,ActionForm af,HttpServletRequest req,</div>
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                                                                                HttpServletResponse
res)throws Exception{</div>
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                String
uname= req.getParameter(“uname”);</div>
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                String
pass=req.getParameter(“pass”);</div>
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                LoginModel
lm = new LoginModel();</div>
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                String
type=lm.validate(uname,pass);</div>
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                If(type==null)return
am.findForward(“notValid”);</div>
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                Return am.findForward(type);</div>
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}//execute</div>
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}//class</div>
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<br></div>
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<span style="font-family: "Georgia","serif"; font-size: 12.0pt; line-height: 115%;">As show in the above
LoginAction execute() method is invoking the validate() method on the
LogingModel object where LoginModel is a plain java classs designed to perform
business logic operation in this case validate the login details, the listing shows
the LoginModel.java<o:p></o:p></span></div>
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<br></div>
</div>

The Action Class

The action class is a class that is a subtype of org.apache.struts.action.Action. The action class that is a part of controller provdes...

The RequestProcessor

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<span style="font-family: "Georgia","serif"; font-size: 12.0pt; line-height: 115%;"><br></span></div>
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<span style="font-family: "Georgia","serif"; font-size: 12.0pt; line-height: 115%;">The RequestProcessor  of Struts framework is an implementation of
Application Controller pattern that takes many infrastructure responsibilities
mainly Action management and View Management. The RequestProcessor is a plain
Java class. The object is created and initialized by the Action Servlet while
the ActionServlet is being initialized as explained in the above section, this
class implements importantly three public methods that allows the ActionServlet
to initialize the module, delegate request to process, and destroy the module,
the method signature of these methods is shown in the below given snippet.<o:p></o:p></span></div>
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<span style="font-family: "Georgia","serif"; font-size: 12.0pt; line-height: 115%;"><br></span></div>
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Code Snippet</div>
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  1.<span style="font-size: 7pt;">      
</span>Public void init                   (org.apche.struts.action.ActionServlet,org.apache.struts.config.</div>
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ModuleConfig)throws
javax.servlet.ServletException</div>
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<br></div>
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  2.<span style="font-size: 7pt;">      
</span>Public void process          (javax.servlet.http.HttpServletRequest,javax.servlet.http</div>
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.HttpServletReesponse)throws java.io.IOException,</div>
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Javax.servlet.ServletException</div>
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<br></div>
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  3.<span style="font-size: 7pt;">      
</span>Public void destroy()</div>
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<br></div>
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<br></div>
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<span style="font-family: "Georgia","serif"; font-size: 12.0pt; line-height: 115%;">As shown in the above code
snippet init() method of the RequestProessor takes two arguments one is
ActionServlet and the second is ModuleConfig. As described in the above section
in the initialization process of ActionServlet, it creates a ModuleConfig object
encapsulating the descriptions of the module configured in the respective
struts configuration file. The ActionServlet creates an instance of
RequestProcessor instance newly created injecting its instance reference(i.e
ActionServlet) and ModuleConfilg, which initializes the RequestProcessor
instance making it prepared to handle the client request for this module. In
case of any problem in initialization, RequestProcessor throws a
ServletException to the ActionServlet.<o:p></o:p></span><br>
<span style="font-family: "Georgia","serif"; font-size: 12.0pt; line-height: 115%;"></span><br>
</div></div>

The RequestProcessor

The RequestProcessor of Struts framework is an implementation of Application Controller pattern that takes many infrastructure respo...