Programming for beginners: Spring: Working with WebApplicationInitializer

WebApplicationInitializer is used to configure ServletContext programatically. SpringServletContainerInitializer detect the classes that implements WebApplicationInitializer interface on application start up time.

Traditional XML based approach

web.xml

<web-app id="WebApp_ID" version="2.4"
 xmlns="http://java.sun.com/xml/ns/j2ee"
 xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
 xsi:schemaLocation="http://java.sun.com/xml/ns/j2ee 
   http://java.sun.com/xml/ns/j2ee/web-app_2_4.xsd">

 <display-name>Spring MVC Hello WorldApplication</display-name>

 <servlet>
  <servlet-name>HelloWorld</servlet-name>
  <servlet-class>org.springframework.web.servlet.DispatcherServlet</servlet-class>

  <init-param>
   <param-name>contextConfigLocation</param-name>
   <param-value>/WEB-INF/myWebAppConfigurations.xml</param-value>
  </init-param>
  <load-on-startup>1</load-on-startup>
 </servlet>

 <servlet-mapping>
  <servlet-name>HelloWorld</servlet-name>
  <url-pattern>/</url-pattern>
 </servlet-mapping>

</web-app>

We can rewrite above web.xml file programmatically like below.

ApplicationInitializer.java

package com.sample.myApp.initializers;

import javax.servlet.ServletContext;
import javax.servlet.ServletException;
import javax.servlet.ServletRegistration;

import org.springframework.web.WebApplicationInitializer;
import org.springframework.web.context.support.XmlWebApplicationContext;
import org.springframework.web.servlet.DispatcherServlet;

public class ApplicationInitializer implements WebApplicationInitializer {

 public void onStartup(ServletContext servletContext) throws ServletException {
  XmlWebApplicationContext appContext = new XmlWebApplicationContext();
  appContext.setConfigLocation("/WEB-INF/myWebAppConfigurations.xml");

  ServletRegistration.Dynamic dispatcher = servletContext.addServlet("HelloWorld",
    new DispatcherServlet(appContext));
  dispatcher.setLoadOnStartup(1);
  dispatcher.addMapping("/");
 }

}

Find the below working application.

HelloWorldController.java

package com.sample.myApp.controllers;

import org.springframework.stereotype.Controller;
import org.springframework.ui.ModelMap;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RequestMethod;

@Controller
@RequestMapping("/hello")
public class HelloWorldController {

 @RequestMapping(method = RequestMethod.GET)
 public String printHello(ModelMap model) {
  model.addAttribute("message", "Welcome to Spring MVC framework");

  return "hello";
 }

}

Create ‘hello.jsp’ file under WEB-INF/jsp folder.

hello.jsp

<%@ page language="java" contentType="text/html; charset=ISO-8859-1"
 pageEncoding="ISO-8859-1"%>
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=ISO-8859-1">
<title>Hello World Spring Web MVC</title>
</head>
<body>
 <h2>${message}</h2>
</body>
</html>

Create ‘myWebAppConfigurations.xml’ file under WEB-INF.

myWebAppConfigurations.xml

<beans xmlns="http://www.springframework.org/schema/beans"
 xmlns:context="http://www.springframework.org/schema/context"
 xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
 xsi:schemaLocation="
   http://www.springframework.org/schema/beans     
   http://www.springframework.org/schema/beans/spring-beans-3.0.xsd
   http://www.springframework.org/schema/context 
   http://www.springframework.org/schema/context/spring-context-3.0.xsd">

 <context:component-scan base-package="com.sample.myApp" />

 <bean
  class="org.springframework.web.servlet.view.InternalResourceViewResolver">
  <property name="prefix" value="/WEB-INF/jsp/" />
  <property name="suffix" value=".jsp" />
 </bean>

</beans>

index.jsp

<html>
<body>
 <h2>Hello World!</h2>
</body>
</html>

Project structure looks like below.

Run above application and hit the url http://localhost:8080/springdemo/hello.

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Programming for beginners

Monday, 12 November 2018

Spring: Working with WebApplicationInitializer

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