1. 简介
Spring MVC是一个创建Web应用程序的框架，它是遵循Model-View-Controller的设计模式。
Spring MVC通过DispatcherServlet来接收请求，然后对应对具体的controllers, models和views.
2. 一个HelloWorld事例
1. 添加maven依赖
<dependency>
<groupId>org.springframework</groupId>
<artifactId>spring-webmvc</artifactId>
<version>5.3.37</version>
</dependency>
<dependency>
<groupId>javax.servlet</groupId>
<artifactId>javax.servlet-api</artifactId>
<version>3.1.0</version>
<scope>provided</scope>
</dependency>2. 在Web.xml中添加DispatcherServlet
<!DOCTYPE web-app PUBLIC
"-//Sun Microsystems, Inc.//DTD Web Application 2.3//EN"
"http://java.sun.com/dtd/web-app_2_3.dtd" >
<web-app xmlns="http://xmlns.jcp.org/xml/ns/javaee"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/javaee http://xmlns.jcp.org/xml/ns/javaee/web-app_4_0.xsd"
version="4.0">
<servlet>
<servlet-name>springmvc</servlet-name>
<servlet-class>org.springframework.web.servlet.DispatcherServlet</servlet-class>
<init-param>
<param-name>contextConfigLocation</param-name>
<param-value>classpath:springmvc.xml</param-value>
</init-param>
<load-on-startup>1</load-on-startup>
</servlet>
<servlet-mapping>
<servlet-name>springmvc</servlet-name>
<url-pattern>/</url-pattern>
</servlet-mapping>
</web-app>3. 在resources目录下面添加springmvc.xml
<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xmlns:mvc="http://www.springframework.org/schema/mvc"
xmlns:context="http://www.springframework.org/schema/context"
xsi:schemaLocation="
http://www.springframework.org/schema/beans
http://www.springframework.org/schema/beans/spring-beans.xsd
http://www.springframework.org/schema/context
http://www.springframework.org/schema/context/spring-context.xsd
http://www.springframework.org/schema/mvc
http://www.springframework.org/schema/mvc/spring-mvc.xsd">
<mvc:annotation-driven />
<context:component-scan base-package="com.example"/>
<bean id="viewResolver" class="org.springframework.web.servlet.view.InternalResourceViewResolver">
<property name="prefix" value="/"></property>
<property name="suffix" value=".jsp"></property>
</bean>
</beans>4. 添加controller
@Controller
@RequestMapping("/hello")
public class HelloController {
@GetMapping("/world")
public String world(Model model){
model.addAttribute("message", "hello world, everyone!");
return "hello";
}
}5. 添加hello.jsp文件
<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<%@ page isELIgnored="false"%>
<html>
<head>
<title>Title</title>
</head>
<body>
<h1>${message}</h1>
</body>
</html>6. 整个目录结构如下：
7. 启动，访问
http://localhost:8080/hello/world
3. 纯代码方式启动SpringMVC
1. 创建注册DispatcherServlet的类，Spring给我们提供了一个抽象的AbstractDispatcherServletInitializer，我们继承它就好了
public class ServletInitConfig extends AbstractDispatcherServletInitializer {
protected WebApplicationContext createServletApplicationContext() {
AnnotationConfigWebApplicationContext context = new AnnotationConfigWebApplicationContext();
context.register(SpringMvcConfig.class);
return context;
}
protected String[] getServletMappings() {
return new String[]{"/"};
}
protected WebApplicationContext createRootApplicationContext() {
return null;
}
}2. 添加SpringMvcConfig.java
@Configuration
@ComponentScan("com.example")
public class SpringMvcConfig {
@Bean
public InternalResourceViewResolver viewResolver(){
InternalResourceViewResolver viewResolver = new InternalResourceViewResolver();
viewResolver.setPrefix("/");
viewResolver.setSuffix(".jsp");
return viewResolver;
}
}3. 创建controller
@Controller
public class HelloController {
@RequestMapping("/hello")
public String hello(Model model){
model.addAttribute("message", "hello world 2!");
return "hello";
}
}4. 创建hello.jsp
<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<%@ page isELIgnored="false"%>
<html>
<head>
<title>Title</title>
</head>
<body>
<h2>${message}</h2>
</body>
</html>5. 代码结构如下，去除了前面的web.xml和springmvc.xml, 改用代码来配置
6. 访问：http://localhost:8080/hello
7. 原理
在Servlet3.0环境中，容器会在类路径中查找实现javax.servlet.ServletContainerInitializer接口的类，如果找到的话就用它来配置Servlet容器，servlet3.0赋予了web项目免去所有配置文件（web.xml）的能力。
可以自定义一个实现ServletContainerInitializer接口，这个类必须在jar包的META-INF/services/javax.servlet.ServletContainerInitializer文件里面进行声明，这个文件的内容就是自定义类的全类名。注意看下面spring-web模块里面的配置
SpringServletContainerInitializer类定义如下：
@HandlesTypes({WebApplicationInitializer.class})
public class SpringServletContainerInitializer implements ServletContainerInitializer {
public SpringServletContainerInitializer() {
}
public void onStartup(@Nullable Set<Class<?>> webAppInitializerClasses, ServletContext servletContext) throws ServletException {
}
}注意这个类上面的@HandlesTypes注解，servlet容器会扫描项目中的所有类，如果符合@HandlesTypes注解value值指定的类型，就会放在一个数组中，最终会传递给onStartup方法的第一个参数。
我们再来看一下AbstractDispatcherServletInitializer类, 它就实现了WebApplicationInitializer接口
public abstract class AbstractDispatcherServletInitializer extends AbstractContextLoaderInitializer
public abstract class AbstractContextLoaderInitializer implements WebApplicationInitialize