Spring MVC
Spring MVC是目前主流的实现MVC设计模式的企业级开发框架，Spring框架的一个子模块，无需整合，开发起来更加便捷。
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什么是MVC设计模式
将应用程序分为Control、Model、View三层，Controller接受客户端请求，调用Model生成业务数据，传递个View。
Spring MVC就是对这套流程的封装，屏蔽了很多底层代码，开放出接口，使开发者更加轻松和便捷的开发出web应用
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Spring MVC的核心组件
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Spring MVC的工作流程
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SpringMVC流程非常复杂，实际开发起中很简单，因为大部分的组件不需要开发者创建、管理，只需要通过配置文件的方式完成配置即可。真正需要开发者进行处理的只有Handler、View。
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如何使用？
1.创建maven工程，pom.xml
????1???????<dependency>
????2?????????????<groupId>org.springframework</groupId>
????3?????????????<artifactId>spring-webmvc</artifactId>
????4?????????????<version>5.0.11.RELEASE</version>
????5?????????</dependency>
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2.在web.xml添加一个servlet。
????1?<!DOCTYPE web-app PUBLIC
????2???"-//Sun Microsystems, Inc.//DTD Web Application 2.3//EN"
????3???"http://java.sun.com/dtd/web-app_2_3.dtd" >
????4?
????5?<web-app>
????6?????<display-name>Archetype Created Web Application</display-name>
????7?????<servlet>
????8?????????<servlet-name>dispatcherServlet</servlet-name>
????9?????????<servlet-class>org.springframework.web.servlet.DispatcherServlet</servlet-class>
???10?????????<init-param>
???11?????????????<param-name>contextConfigLocation</param-name>
???12?????????????<param-value>classpath:springmvc.xml</param-value>
???13?????????</init-param>
???14?????</servlet>
???15?????
???16?????<servlet-mapping>
???17?????????<servlet-name>dispatcherServlet</servlet-name>
???18?????????<url-pattern>/</url-pattern>
???19?????</servlet-mapping>
???20?</web-app>
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3.springmvc.xml中进行配置
????1?<?xml version="1.0" encoding="UTF-8"?>
????2?<beans xmlns="http://www.springframework.org/schema/beans"
????3???????????????xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
????4???????????????xmlns:context="http://www.springframework.org/schema/context"
????5???????????????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">
????6?????????????????
????7?????????<!-- 自动扫描 -->
????8?????????<context:component-scan base-package="com.wiggin"></context:component-scan>
????9?????????
???10?????????<!-- 视图解析器(逻辑视图解析成物理视图) -->
???11?????????<bean class="org.springframework.web.servlet.view.InternalResourceViewResolver">
???12?????????????????<!-- 前置字符和后置字符 -->
???13?????????????????<property name="prefix" value="/"></property>
???14?????????????????<property name="suffix" value=".jsp"></property>
???15?????????</bean>
???16?</beans
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4.创建Handler
????1?package com.wiggin.controller;
????2?
????3?import org.springframework.stereotype.Controller;
????4?import org.springframework.web.bind.annotation.RequestMapping;
????5?
????6?@Controller // 交给了ioc以及包含了控制器功能
????7?public class HelloHandler {
????8?????????@RequestMapping("/index") // 返回给index视图
????9?????????public String index(){
???10?????????????????System.out.printf("执行了index..");
???11?????????????????return "index";
???12?????????}
???13?}
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注解：
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Spring MVC通过@RequestMapping注解将URL请求与业务方法进行映射，在Handler的类定义处以及方法定义处都可以添加@RequestMapping，在类定义处添加，相当于客户端多了一层访问路径。
相关参数：
1.value:指定URL请求地实际地址，是@RequestMapping的默认值
????1?@RequestMapping("/index") // 返回给index视图
????2?public String index(){
????3?????????System.out.printf("执行了index..");
????4?????????return "index";
????5?}
等于
????1???@RequestMapping(value = "/index") // 返回给index视图
????2?????????public String index(){
????3?????????????????System.out.printf("执行了index..");
????4?????????????????return "index";
????5?????????}
2.method: 指定请求method类型，GET,POST,PUT,DELET。
????1?@RequestMapping(value = "/index",method = RequestMethod.GET) // 返回给index视图
????2? public String index(){
????3?????????System.out.printf("执行了index..");
????4?????????return "index";
????5? }
index的方法只能使用GET请求。
3.parms: 请求中必须包含的参数，否则无法调用该方法
????1?@RequestMapping(value = "/index",method = RequestMethod.GET,params = {"name","id=10"}) // 返回给index视图
????2? public String index(){
????3?????????System.out.printf("执行了index..");
????4?????????return "index";
????5? }
关于参数绑定，在形参列表中通过添加@RequestParam注解完成Http请求参数与业务方法的形参的映射。
????1?@RequestMapping(value = "/index",method = RequestMethod.GET,params = {"name","age=10"}) // 返回给index视图
????2?public String index(String name,@RequestParam("age") int id){
????3?????????System.out.println(name);
????4?????????System.out.println(id);
????5?????????System.out.println("执行了index..");
????6?????????return "index";
????7?}
上述代码的中的请求参数name和age分别赋值给了形参name和age,HandlerAdaptor请求参数name和age的类型自动转型为形参name和age的形式。
执行原理：DispatcherServlet捕获url，根据HandlerMapping映射到Handler，即有@RequestMapping("/index")的@Controller，由springmvc执行方法，最后返回逻辑视图到DispatcherServlet中，由ViewResolver将返回视图名添加前后缀，变为物理视图，最后找到target文件所对应的jsp文件，将其返回给客户端。
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补充：Spring MVC也支持RESTful风格的URL。
传统类型 http://localhost:8080/hello/index?name=wiggin&age=10
REST： http://localhost:8080/hello/index/wiggin/10
????1?@RequestMapping("/rest/{name}/{age}")
????2?public String rest(@PathVariable("name") String name,@PathVariable("age") int age){
????3?????????System.out.println(name);
????4?????????System.out.println(age);
????5?????????return "index";
????6?}
REST风格URL必须要加@PathVariable来完成参数映射数映射
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Spring MVC通过映射可以直接在业务方法中获取cookie的值
????1?@RequestMapping("/cookie")
????2?public String cookie(@CookieValue(value = "JSESSIONID") String sessionId){
????3?????????System.out.println(sessionId);
????4?????????return "index";
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Spring MVC会根据请求参数名和javaBean属性名进行自动匹配，自动为对象填充属性值，同时支持及联属性。
????1?package com.wiggin.entity;
????2?
????3?import lombok.Data;
????4?
????5?@Data
????6?public class Address {
????7?????????private String value;
????8?}
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----
????1?package com.wiggin.entity;
????2?
????3?import lombok.Data;
????4?
????5?@Data
????6?public class User {
????7?????????private long id;
????8?????????private String name;
????9?????????private Address address;
???10?}
----
????1?<%--
????2?????Created by IntelliJ IDEA.
????3?????User: Administrator
????4?????Date: 2020/8/3
????5?????Time: 22:12
????6?????To change this template use File | Settings | File Templates.
????7?--%>
????8?<%@ page contentType="text/html;charset=UTF-8" language="java" %>
????9?<html>
???10?<head>
???11?????????<title>Title</title>
???12?</head>
???13?<body>
???14?????????<form action="/hello/save" method="post">
???15?????????????????用户id:<input type="text" name="id"></br>
???16?????????????????用户名:<input type="text" name="name"></br>
???17?????????????????用户地址:<input type="text" name="address.value"></br>
???18?????????????????<input type="submit" value="注册">
???19?????????</form>
???20?</body>
???21?</html>
----
????1?@RequestMapping(value = "/save",method = RequestMethod.POST)
????2?public String save(User user){
????3?????????System.out.println(user);
????4?????????return "index";
????5?}
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防止输入的值传入后台时中文出现乱码需要在web.xml中配置过滤器
????1?<!-- 过滤器 -->
????2?????<filter>
????3?????????<filter-name>encodingFilter</filter-name>
????4?????????<filter-class>org.springframework.web.filter.CharacterEncodingFilter</filter-class>
????5?????????<init-param>
????6?????????????<param-name>encoding</param-name>
????7?????????????<param-value>UTF-8</param-value>
????8?????????</init-param>
????9?????</filter>
???10?
???11?????<!-- 拦截所有的请求 -->
???12?????<filter-mapping>
???13?????????<filter-name>encodingFilter</filter-name>
???14?????????<url-pattern>/*</url-pattern>
???15?????</filter-mapping>
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Spring MVC默认是转发的形式来响应JSP
1.转发
????1?@RequestMapping("/forward")
????2?public String forward(){
????3?????????return "forward:/index.jsp";
????4?????????// 相当于 return "index";
????5?}
2.重定向
????1?@RequestMapping("/redirect")
????2?????????public String redirect(){
????3?????????????????return "redirect:/index.jsp";
????4?????????}
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原文：https://www.cnblogs.com/wigginess/p/13447383.html