Introduction To Struts

Introduction to Struts

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Agenda  Servlet

BackGround

– Servlets, JSP, web.xml – Request processing flow , issues with Servlets  Struts

Components  HelloWorld Application  Exercise

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Servlets  Servlet

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flow of execution

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JSP  JSP

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flow of execution

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Issues with JSP and servlets  Real

issues

– – – – – –

Servlets embed html into code JSP embeds code into GUI Project time increases Not modular Reuse is difficult Server side programmers are not comfortable with GUI code and vice versa – If target of GUI is changed, server side code gets affected. Unnat-e

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Struts Overview  MVC

architecture for Web based applications  Separates view (JSP) from model (java code).

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Struts overview (Request flow)

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Struts Components ActionServlet  ActionServlet

– This is the main struts class. It is a servlet. An application that uses struts directs all the requests to the ActionServlet class by specifying a url mapping in the web.xml file.

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Struts Components – strutsconfig.xml  Similar

to web.xml, this is specified as a parameter in web.xml  It contains two broad categories of information – Configuration information for struts – Action-mappings  Struts-config

entries

– Form beans, action-mappings Unnat-e

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Struts Components – ActionMappings  An

action mapping entry in the struts config file maps a url to a model and a view.  The model is an action class  The view is a jsp file

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Struts Components – Action Classes  Action

classes populate the model when a request is made – for example if a request is made to view the details of an employee with a particular id, then the model will retrieve the details of the employee using the id.  Action classes should be written by the application programmer  Action classes should extend org.apache.struts.action.Action Unnat-e

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Struts Components – Action classes  Action

classes need to override the following method  Public ActionForward execute  Takes following parameters – – – – Unnat-e

ActionMapping mapping ActionForm form HTTPRequest request HTTPResponse response 12 10/14/08

Struts Components – ActionForm  Action

classes need to access to form variables. In servlets, this is done via request.getParameter()  Struts allows the programmer to define a bean called an ActionForm object. This bean should contain variables with the same name as the variables in the form.  An entry should be made in the form-beans section of struts-config.xml for this class  An entry should be made in the action mapping for this url Unnat-e

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Struts Components – ActionForm population mechanism  When a request arrives, struts checks the struts

config.xml and retrieves the action-mapping corresponding to the url.  It checks if there is a name parameter corresponding to the action mapping  If there is a name parameter, struts finds out the corresponding class name from the form bean entry  It creates an object of this type.  It now traverses via all the members of this object via reflection, looks up corresponding variables from the request and populates the form Unnat-e object.

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Struts Components – request flow details  Tomcat

forwards request to ActionServlet  ActionServlet retrieves action-mapping from struts-config.xml  ActionServlet creates Actionform object  ActionServlet creates Action object  ActionServlet invokes execute on Action  Action performs action directly or by delegating to business logic  Action creates model and stores it into session  Action returns a Forward  Action Servlet retrieves JSP corresponding to Unnat-e Forward and forwards to the jsp

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Struts Components – JSP tag libs  Struts

provides a rich set of tag libraries which can be used in jsp pages  HTML tag libs can be used to create jsp forms rapidly  Logic tag libs are used to do evaluation of expressions and decision making  Bean tag libs are used to manipulate java beans, cookies, and http headers Unnat-e

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The first struts Application  Application

shows a small form with a

message  Enter Name  <submit> button  On submitting, it should show a screen with hardcoded details of username.

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