SpringMVC 原理

一、先来敲一个helloSpringMVC的代码。
1.pom.xml:因为springMVC 是spring框架的一部分，所以导包就还是spring-webmvc,再加上servlet、jsp、jstl包

<?xml version="1.0" encoding="UTF-8"?>
<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/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>
    <groupId>com.eiji</groupId>
    <artifactId>SpringMVC</artifactId>
    <packaging>pom</packaging>
    <version>1.0-SNAPSHOT</version>
    <modules>
        <module>springmvc-01-servlet</module>
        <module>springmvc-02-hellomvc</module>
    </modules>
    <dependencies>
        <!-- https://mvnrepository.com/artifact/log4j/log4j -->
        <dependency>
            <groupId>log4j</groupId>
            <artifactId>log4j</artifactId>
            <version>1.2.17</version>
        </dependency>
        <!--junit-->
        <dependency>
            <groupId>junit</groupId>
            <artifactId>junit</artifactId>
            <version>4.13</version>
            <scope>test</scope>
        </dependency>
        <dependency>
            <groupId>org.springframework</groupId>
            <artifactId>spring-webmvc</artifactId>
            <version>5.3.8</version>
        </dependency>
        <dependency>
            <groupId>javax.servlet</groupId>
            <artifactId>servlet-api</artifactId>
            <version>2.5</version>
        </dependency>
        <dependency>
            <groupId>javax.servlet.jsp</groupId>
            <artifactId>jsp-api</artifactId>
            <version>2.2</version>
        </dependency>
        <dependency>
            <groupId>javax.servlet</groupId>
            <artifactId>jstl</artifactId>
            <version>1.2</version>
        </dependency>
    </dependencies>
</project>

2.将项目添加web支持，右键Add Framework Support
3.web.xml:

<?xml version="1.0" encoding="UTF-8"?>
<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">
    <!--DispatcherServlet：springmvc的核心；请求分发器；前端控制器-->
    <servlet>
        <servlet-name>springMVC</servlet-name>
        <servlet-class>org.springframework.web.servlet.DispatcherServlet</servlet-class>
        <!--绑定spring配置文件-->
        <init-param>
            <param-name>contextConfigLocation</param-name>
            <param-value>classpath:springmvc-servlet.xml</param-value>
        </init-param>
        <!--启动等级-->
        <load-on-startup>1</load-on-startup>
    </servlet>
    <!--
    /   :匹配所有的请求，但不包括jsp
    /*  :匹配所有的请求，包括jsp
    -->
    <servlet-mapping>
        <servlet-name>springMVC</servlet-name>
        <url-pattern>/</url-pattern>
    </servlet-mapping>
</web-app>

4.springmvc-servlet.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"
       xsi:schemaLocation="http://www.springframework.org/schema/beans
       http://www.springframework.org/schema/beans/spring-beans.xsd">
    <!--处理器映射器-->
    <bean class="org.springframework.web.servlet.handler.BeanNameUrlHandlerMapping"/>
    <!--处理器适配器-->
    <bean class="org.springframework.web.servlet.mvc.SimpleControllerHandlerAdapter"/>
    <!--视图解析器-->
    <bean class="org.springframework.web.servlet.view.InternalResourceViewResolver" id="internalResourceViewResolver">
        <property name="prefix" value="/WEB-INF/jsp/"/>
        <property name="suffix" value=".jsp"/>
    </bean>
    <bean id="/hello" class="com.eiji.controller.HelloController"/>
</beans>

5.HelloController

public class HelloController implements Controller {
    public ModelAndView handleRequest(HttpServletRequest httpServletRequest, HttpServletResponse httpServletResponse) throws Exception {
        ModelAndView mv = new ModelAndView();
        // 业务代码
        String result = "hello springmmvc";
        mv.addObject("msg",result);
        // 视图跳转
        mv.setViewName("hello");
        return mv;
    }
}

6.jsp

二、原理解释
1.所有请求都会到web.xml 被捕获，进而到DispatcherServlet核心控制处，DispatcherServlet根据绑定的spring配置文件到达springmvc-config.xml。
2.处理器映射器BeanNameUrlHandlerMapping找到/hello，然后将解析后的信息返回DispatcherServlet核心控制处
3.处理器适配器SimpleControllerHandlerAdapter根据hello找到HelloController，HelloController经过处理之后会将想向前端传递的数据和请求的名字封装好，返回ModelAndView。
4.视图解析器会获取ModelAndView中的数据，然后解析ModelAndView的视图名字，然后拼接视图名字，找到对应的视图，最后将数据渲染到这个视图上。实际上视图解析器是将解析好的视图名字传递给DispatcherServlet，DispatcherServlet根据视图解析器解析的视图结果调用具体的视图，最后呈现。