In this tutorial, we will show you a Spring MVC hello world web application.
Technologies used :
- Spring 2.5.6
- JDK 1.6
- Eclipse 3.6
- Maven 3
1. MVC Basic
In Spring MVC web application, it consists of 3 standard MVC (Model, Views, Controller) components :
- Models – Domain objects that are processed by the service layer (business logic) or persistent layer (database operation).
- Views – Display data, normally it’s a JSP page written with the Java Standard Tag Library (JSTL).
- Controllers – URL mapping and interact with service layer for business processing and return a Model.
The following figures demonstrates how the Spring MVC web application handles a web request.
Figure 1.1 – Image is copied from Spring MVC reference with slightly modified.
这个图片比较全面的说明了 spring mvc的工作过程， 很重要的， 需要多多理解。
Figure 1.2 – Image is copied from this book : Spring Recipes
Note
In Spring MVC , the core dispatcher component is the DispatcherServlet, which act as the front-controller (design pattern). Every web request has to go through this DispatcherServlet, and the DispatcherServlet will dispatch the web request to suitable handlers.
2. Directory Structure
A standard Maven project directory structure.
3. Maven
Declares the spring-webmvc dependency, Maven will help you manage the transitive dependencies automatically (download other dependencies that are required by spring-webmvc, like spring-context or spring-beans).
If you are using the JSP page with JSTL technology, include the jstl dependency also.
pom.xml
<project xmlns="http://maven.apache.org/POM/4.0.0"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://maven.apache.org/POM/4.0.0
http://maven.apache.org/maven-v4_0_0.xsd">
<modelVersion>4.0.0</modelVersion>
<groupId>com.mkyong.common</groupId>
<artifactId>spring2-mvc-xml-hello-world</artifactId>
<packaging>war</packaging>
<version>1.0-SNAPSHOT</version>
<name>Spring 2 MVC</name>
<properties>
<jdk.version>1.6</jdk.version>
<spring.version>2.5.6</spring.version>
<jstl.version>1.2</jstl.version>
<servletapi.version>2.5</servletapi.version>
</properties>
<dependencies>
<dependency>
<groupId>org.springframework</groupId>
<artifactId>spring-webmvc</artifactId>
<version>${spring.version}</version>
</dependency>
<dependency>
<groupId>javax.servlet</groupId>
<artifactId>jstl</artifactId>
<version>${jstl.version}</version>
</dependency>
<dependency>
<groupId>javax.servlet</groupId>
<artifactId>servlet-api</artifactId>
<version>${servletapi.version}</version>
<scope>provided</scope>
</dependency>
</dependencies>
<build>
<plugins>
<plugin>
<groupId>org.apache.maven.plugins</groupId>
<artifactId>maven-compiler-plugin</artifactId>
<version>3.3</version>
<configuration>
<source>${jdk.version}</source>
<target>${jdk.version}</target>
</configuration>
</plugin>
<plugin>
<groupId>org.eclipse.jetty</groupId>
<artifactId>jetty-maven-plugin</artifactId>
<version>9.2.11.v20150529</version>
<configuration>
<scanIntervalSeconds>10</scanIntervalSeconds>
<webApp>
<contextPath>/spring2</contextPath>
</webApp>
</configuration>
</plugin>
<plugin>
<groupId>org.apache.maven.plugins</groupId>
<artifactId>maven-eclipse-plugin</artifactId>
<version>2.9</version>
<configuration>
<downloadSources>true</downloadSources>
<downloadJavadocs>true</downloadJavadocs>
<wtpversion>2.0</wtpversion>
<wtpContextName>spring2</wtpContextName>
</configuration>
</plugin>
</plugins>
</build>
</project>
4. Spring Controller
Spring comes with many Controllers, normally, you just need to extend the AbstractController, and override the handleRequestInternal() method.
HelloWorldController.java
package com.mkyong.common.controller;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import org.springframework.web.servlet.ModelAndView;
import org.springframework.web.servlet.mvc.AbstractController;
public class HelloWorldController extends AbstractController{
@Override
protected ModelAndView handleRequestInternal(HttpServletRequest request,
HttpServletResponse response) throws Exception {
ModelAndView model = new ModelAndView("HelloWorldPage");
model.addObject("msg", "hello world");
return model;
}
}
4.1 ModelAndView(“HelloWorldPage”) – To identify which view should return back to the user, in this example HelloWorldPage.jsp will be returned.
4.2 model.addObject(“msg”, “hello world”) – Add a “hello world” string into a model named “msg”, later you can use EL ${msg} to display the “hello world” string.
5. View (JSP page)
In this case, “view” is a JSP page, you can display the value “hello world” that is stored in the model “msg” via expression language (EL) ${msg}.
HelloWorldPage.jsp
<%@ taglib prefix="c" uri="http://java.sun.com/jsp/jstl/core"%>
<html>
<body>
<h1>Spring MVC Hello World Example</h1>
<h2>${msg}</h2>
</body>
</html>
Note If the ${msg} is displayed as it is, not the value inside the “msg” model, it may caused by the old JSP 1.2 descriptor, which make the expression languages disabled by default, see the
solution here.
6. Spring XML Configuration
6.1 Declared the Spring Controller and viewResolver.
mvc-dispatcher-servlet.xml
<beans xmlns="http://www.springframework.org/schema/beans"
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-2.5.xsd">
<bean name="/welcome.htm"
class="com.mkyong.common.controller.HelloWorldController" />
<bean id="viewResolver"
class="org.springframework.web.servlet.view.InternalResourceViewResolver" >
<property name="prefix">
<value>/WEB-INF/pages/</value>
</property>
<property name="suffix">
<value>.jsp</value>
</property>
</bean>
</beans>
1. Controller – Declared a bean name /welcome.htm and map it to HelloWorldController. It means, if an URL with /welcome.htm pattern is requested, the HelloWorldController controller will handle the request.
2. viewResolver – Define how Spring will look for the view template. In this case, the controller HelloWorldController will return a view named HelloWorldPage, the viewResolver will find the file with following mechanism : prefix + view name + suffix, which is /WEB-INF/pages/HelloWorldPage.jsp.
Note Actually, you don’t need to define the
BeanNameUrlHandlerMapping in the
web.xml, by default, if no handler mapping can be found, the DispatcherServlet will create a
BeanNameUrlHandlerMapping automatically. See this article –
BeanNameUrlHandlerMapping example for detail.
6.2 In web.xml, declared a DispatcherServlet servlet to act as the front-controller to handle all the entire web request which end with htm extension.
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 Web MVC Application</display-name>
<servlet>
<servlet-name>mvc-dispatcher</servlet-name>
<servlet-class>
org.springframework.web.servlet.DispatcherServlet
</servlet-class>
<load-on-startup>1</load-on-startup>
</servlet>
<servlet-mapping>
<servlet-name>mvc-dispatcher</servlet-name>
<url-pattern>*.htm</url-pattern>
</servlet-mapping>
</web-app>
Note
The mvc-dispatcher is used to define which file to load the Spring XML configurations. By default, it will look for Spring XML configuration file by joining the servlet name mvc-dispatcher with -servlet.xml.In this example, Spring will look for this file – mvc-dispatcher-servlet.xml.
7. Demo
7.1 To run this project with Maven :
$ mvn jetty:run
7.2 To run this project in Eclipse IDE, create Eclipse project settings with the following Maven command :
$ mvn eclipse:eclipse
Imports the project manually and start with the server plugin.
URL : http://localhost:8080/spring2/welcome.htm
How it works?
- http://localhost:8080/spring2/welcome.htm is requested.
- URL is end with “.htm” extension, so it will redirect to “DispatcherServlet” and send requests to the default BeanNameUrlHandlerMapping.
- BeanNameUrlHandlerMapping return HelloWorldController to the DispatcherServlet.
- DispatcherServlet forward request to the HelloWorldController.
- HelloWorldController process it and return a ModelAndView object, with view name “HelloWorldPage”.
- DispatcherServlet received the ModelAndView and call the viewResolver to process it.
- viewResolver return the
/WEB-INF/pages/HelloWorldPage.jsp back to the DispatcherServlet. - DispatcherServlet return the “HelloWorldPage.jsp” back to the user.
Download Source Code
References
- Spring MVC documentation
