Bootstrapping a Spring Web MVC application programmatically

Since Spring framework 3.1+, developers are able to implement a 100% code-based approach for bootstrapping a Spring Web MVC application, without any XML configuration. This tutorial is going to explore how we can achieve that to build a completely XML-free sample Spring Web MVC application.

Usually we create a Spring’s application context file (e.g.  applicationContext.xml ) which configures beans definitions such as view resolver beans, controller beans, DAO beans, application-specific beans, etc. And then we declare Spring’s dispatcher servlet in the web deployment descriptor file ( web.xml ) in order to route all requests through the Spring Web MVC container. For example, following is a typical configuration for bootstrap the Spring’s dispatcher servlet in the  web.xml file:

XML-based approach:

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<? xml version = "1.0" encoding = "UTF-8" ?> < web-app xmlns:xsi = "http://www.w3.org/2001/XMLSchema-instance"      xmlns = "http://java.sun.com/xml/ns/javaee"      xmlns:web = "http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd"      xsi:schemaLocation="http://java.sun.com/xml/ns/javaee          http://java.sun.com/xml/ns/javaee/web-app_3_0.xsd"      id = "WebApp_ID" version = "3.0" >            < display-name >SpringWebMVCApp</ display-name >        < servlet >          < servlet-name >SpringController</ servlet-name >          < servlet-class >org.springframework.web.servlet.DispatcherServlet</ servlet-class >          < init-param >              < param-name >contextConfigLocation</ param-name >              < param-value >/WEB-INF/applicationContext.xml</ param-value >          </ init-param >          < load-on-startup >1</ load-on-startup >      </ servlet >        < servlet-mapping >          < servlet-name >SpringController</ servlet-name >          < url-pattern >/</ url-pattern >      </ servlet-mapping >   </ web-app >

Since Servlet 3.0+, the above registration for Spring’s dispatcher servlet can be done programmatically (code-based), thanks to the Servlet 3.0’s new feature called shared libraries/runtimes pluggability which scans jar files bundled in the  WEB-INF\lib directory for implementations of the  ServletContainerInitializer  interface and invokes its  onStartup()  method which contains initialization/bootstrapping code, during servlet container/web application startup. In respond to this new feature, Spring 3.1+ provides its own implementation by the  SpringServletContainerInitializer  class which is bundled in configured in the  spring-web-VERSION.jar  file.

The  SpringServletContainerInitializer  class is bootstrapped automatically by any Servlet 3.0-compliant container (e.g. Apache Tomcat 7), and it will look for an implementation of the  WebApplicationInitializer  interface and invoke its onStartup()  method. Following is an example of a  WebApplicationInitializer ’s implementation that does the same thing as the XML-based approach above:

Code-based approach:

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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 SpringWebAppInitializer  implements WebApplicationInitializer {        @Override      public void onStartup(ServletContext container)  throws ServletException {          XmlWebApplicationContext appContext =  new XmlWebApplicationContext();          appContext.setConfigLocation( "/WEB-INF/applicationContext.xml" );                    ServletRegistration.Dynamic dispatcher = container.addServlet(                  "SpringDispatcher" ,  new DispatcherServlet(appContext));          dispatcher.setLoadOnStartup( 1 );          dispatcher.addMapping( "/" );      }   }

However, as we can see, the Spring’s application context configuration still remains XML-based:

1	appContext.setConfigLocation( "/WEB-INF/applicationContext.xml" );

We may configure the  applicationContext.xml  file as follows:

XML-based application context configuration:

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< beans xmlns = "http://www.springframework.org/schema/beans"      xmlns:xsi = "http://www.w3.org/2001/XMLSchema-instance"      xmlns:context = "http://www.springframework.org/schema/context"      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">        < bean name = "/" class = "net.codejava.spring.HomeController" />            < bean id = "viewResolver"          class = "org.springframework.web.servlet.view.InternalResourceViewResolver" >          < property name = "prefix" value = "/" />          < property name = "suffix" value = ".jsp" />      </ bean > </ beans >

So to replace this XML by a code-based approach, we can create a configuration class using Spring’s  @Configuration  and @Bean  annotations and register this configuration class by the  AnnotationConfigWebApplicationContext  class.

 

Here’s an example of a replacement for the  applicationContext.xml  above in Java code as follows:

Code-based application context configuration:

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package net.codejava.spring;   import org.springframework.context.annotation.Bean; import org.springframework.context.annotation.Configuration; import org.springframework.web.servlet.mvc.Controller; import org.springframework.web.servlet.view.InternalResourceViewResolver;   @Configuration public class ApplicationContextConfig {            @Bean (name =  "viewResolver" )      public InternalResourceViewResolver getViewResolver() {          InternalResourceViewResolver viewResolver =  new InternalResourceViewResolver();          viewResolver.setPrefix( "/" );          viewResolver.setSuffix( ".jsp" );          return viewResolver;      }            @Bean (name =  "/" )      public Controller getHomeController() {          return new HomeController();      } }

This configuration defines two beans, one for a typical Spring MVC’s view resolver and one for a controller. Code of the HomeController  class is as follows:

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package net.codejava.spring;   import javax.servlet.http.HttpServletRequest; import javax.servlet.http.HttpServletResponse;   import org.springframework.web.servlet.ModelAndView; import org.springframework.web.servlet.mvc.Controller;   public class HomeController  implements Controller {        @Override      public ModelAndView handleRequest(HttpServletRequest request,              HttpServletResponse response)  throws Exception {                    return new ModelAndView( "home" );      }   }

The  handleRequest()  method of this controller class simply returns a logical view name “home” which is mapped to the following  home.jsp  page:

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<%@ page language="java" contentType="text/html; charset=UTF-8"      pageEncoding="UTF-8"%> <!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=UTF-8" > < title >Spring MVC Bootstrap</ title > </ head > < body >      < div align = "center" >          < h1 >Welcome to Spring MVC Bootstrap demo!</ h1 >          < h3 >100% code-based approach, no XML at all!</ h3 >      </ div > </ body > </ html >

And register this configuration file using the  AnnotationConfigWebApplicationContext  class as follows:

1 2	AnnotationConfigWebApplicationContext appContext =  new AnnotationConfigWebApplicationContext(); appContext.register(ApplicationContextConfig. class );

Then we have our  SpringWebAppInitializer  class finalized as follows:

100% code-based approach:

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package net.codejava.spring;   import javax.servlet.ServletContext; import javax.servlet.ServletException; import javax.servlet.ServletRegistration;   import org.springframework.web.WebApplicationInitializer; import org.springframework.web.context.support.AnnotationConfigWebApplicationContext; import org.springframework.web.servlet.DispatcherServlet;   public class SpringWebAppInitializer  implements WebApplicationInitializer {        @Override      public void onStartup(ServletContext container)  throws ServletException {            AnnotationConfigWebApplicationContext appContext =  new AnnotationConfigWebApplicationContext();          appContext.register(ApplicationContextConfig. class );            ServletRegistration.Dynamic dispatcher = container.addServlet(                  "SpringDispatcher" ,  new DispatcherServlet(appContext));          dispatcher.setLoadOnStartup( 1 );          dispatcher.addMapping( "/" );      }   }

If we build this application in Eclipse IDE, we would have the following project structure:

Package and deploy this application on a Servlet 3.0-compliant server (Apache Tomcat) and access it in browser by the following URL:

http://localhost:8080/SpringMVCBootstrap

Output:

As we can see, this simple Spring Web MVC application is running perfectly! Thanks to the code-based approach, we don’t have to write any XML code at all! One big benefit of this approach is that we can package our application’s bootstrap code in a jar file and put it under  WEB-INF\lib  directory and the servlet container will automatically detect and initialize it.

Download the sample application (Eclipse project) to test this out yourself.