Tutorial: - Create a simple web application in net beans using Spring 3.0 MVC

Transcription

1 Tutorial: - Create a simple web application in net beans using Spring 3.0 MVC Objective: - After finishing this tutorial you will be able to do the following things. 1) Can explain the flow of control of a Spring web Appplication. 2) Can write simple applications of redirecting the pages. Tools and frmaeworks used :- Netbeans 7.0.1, Spring 3.0 Concept :- Spring 3.0 is a robust framework which provides MVC features very well for easy and maintainable application development A brief look at MVC, M- Model (A data reprsentation Unit which fetches the data from databse and the populated beans or entities are given back to controller. In a typical web application it is a class which is responsible for gathering the data from database.) V- View (In java world these are genreally jsp's or tiles, i component which is visible to the end user.) C Controller (This unit takes care of the incoming requests and navigate the flow, additinally it associates a view with the model) Spring MVC :- Since you are already familer with Servlets, we can try to understand the spring flow as follows 1) The deplyment descriptor (web.xml) points towards the entry of a spring application which is a severlet provided by Spring as DispatcherServlet. 2) The Dispathcer sevlet receives the request first. 3) The DispatcherServlet looks for an xml file called dispatcher-servlet.xml. 4) DispatcherServelt consults the dispatcher-servlet.xml file to indentify the proper controller for the request. 5) Once the controller is found, the code of the hander method in the Controller executes. 1

2 6) After processing the request a ModelView object is forwarded to Dispather servlet, the model view object consiste of The VIEW NAME and the MODEL Object. 7) Using the View Resolver the DispatcherServlet finds out the appropate view for the response. 8) The corresponding model is given to view 9) View creates the final response using the model provided. Hands on :- If the previos section is clear to you, you are good to go with the hands on now, let us approch our tutorial objective step by step. 1. Open Netbeans Create a new project and give a name as SpringMVC. 3. In frame work selection window select Spring. 4. A project with default prject structure will open. 5. Now open the web.xml file and delete the content of this file. 6. In web.xml write the following code, <?xml version="1.0" encoding="utf-8"?> <web-app version="3.0" xmlns=" xmlns:xsi=" xsi:schemalocation=" <servlet> <servletname>dispatcher</servl et-name> <servletclass>org.springframework.web.servlet.dispatcherservlet</ser vlet-class> <load-on-startup>1</load-on-startup> </s ervl et> <s ervl etma ppi ng > <servlet- 2

3 name>dispatcher</servle t-name> <urlpattern>*.htm</urlpattern> </servlet-mapping> <welcome-file-list> <welcomefile>redirect.jsp</welcom e-file> </w elcom e-filelist> </web -app> Code Explanation :- you can see a servelt named dispatcher is provided to you by Spring frame work, the load-on-start up attribut simply says about the priority of the loading class. In url-mapping you can see that we are attaching looking for.htm extension in order to hide the actual implementation. You can see a redirect.jsp file ourside WEB-INF, This is the only file which is oust side WEB-INF, rest of the jsp's are kept in a folder called jsp in WEB-INF in order to accessable only through the controller. 7.Now open the file called dispatcher-servlet.xml and delete its content. 8.Now write the following code in dispatcher servlet. <?xml version="1.0" encoding="utf-8"?> <beans xmlns=" xmlns:xsi=" xsi:schemalocation=" ma/beans <bean id="viewresolver" 3

4 class="org.springframework.web.servlet.view.internalresourceview Resolver" p:prefix="/web-inf/jsp/" p:suffix=".jsp" /> <bean name="/welcome.htm" class="com.cdac.controller.testcontroller" > <property name="message" value=" Anupam Says Hello!!! " /> </bean> </beans> Code Explanation :- The viewresolver will accept a string which is nothing but a view name and then attaching the given prefix and suffix it will look that view in to the created direstory, for example if a view name bingo is given then the look up formula will look like the following. Lookup for = p:prefix + given View name + p:suffix On sustitution we get a path like /WEB-INF/jsp/bingo.jsp ie it will look for the bingo.jsp file in a directory WEB-INF/jsp. The bean is simply pointing to a java class whcih has a property called message and we are making a setter injection to set a message to this class. Now in next step let us make the class called TestController mentioned in xml. 9. In source folder create a new package as com.cdac.controller. 10. right click on the package and select others => Spring framework =>AbstractController 11. Give the name of the new class as TestController 11. Modify the class TestController as follows 4

5 package com.cdac.controller; import javax.servlet.http.httpservletrequest; import javax.servlet.http.httpservletresponse; import org.springframework.web.servlet.modelandview; import org.springframework.web.servlet.mvc.abstractcontroller; /** * ANUPAM */ public class TestController extends AbstractController { private String message; public String getmessage() { return message; public void setmessage(string message) { this.message = message; public TestController() { protected ModelAndView handlerequestinternal( HttpServletRequest request, HttpServletResponse response) throws Exception { //throw new UnsupportedOperationException("Not yet implemented"); System.out.println("Inside handlerequestinternal"); return new ModelAndView("WelComePage", "WelcomeMessage", message); 5

6 Code Explanation :- Simply this class has a property called message. The task of the class is to process the request and and return a model view object to the DispatcherServlet with 3 paratmeters. The name of the view WelComePage The name of the attribute of the view page (model "WelcomeMessage" name) The object whcih represents the model message 13. Now generate the view of the corresponding controller. 14. Right click on WEB-INF/jsp folder and create a jsp named WelComePage.jsp 15. write the fllowing code in WelComePage.jsp. <%@page contenttype="text/html" pageencoding="utf-8"%> <!DOCTYPE html> <meta http-equiv="content-type" content="text/html; charset=utf-8"> <title>jsp Page</title> <h1>${welcomemessage </h1> </body> </html> Code Explanation :- You can clearly see the the WelComeMessage EL expression, this is what we are trying to set and get printed on the webpage. Now my job is to device a mechanism which will call my test servelt and show me WelComePage.jsp 16.Now open the redirect.jsp at root. 16. Modify the code as below. 6

7 contenttype="text/html" pageencoding="utf-8"%> <%-- response.sendredirect("index.htm"); --%> <% response.sendredirect("welcome.htm"); %> Code Expalantion :- Since the redirect.jsp is listed on the welcome-file-list in web.xml, certainly it will open first as soon as it encounters a send redirect it looks for the appropiate controller, which in our case is the TestController. Test controller sets the view and the model attribule with the injected value. After the view gets resolved the page WelComePage.jsp is rendered on the browser. 7