準(zhǔn)備

新建工程

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pom.xml

<?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.neuedu</groupId>
  <artifactId>springMVC_demo02_response</artifactId>
  <version>1.0-SNAPSHOT</version>
  <packaging>war</packaging>

  <name>springMVC_demo02_response Maven Webapp</name>
  <!-- FIXME change it to the project's website -->
  <url>http://www.example.com</url>

  <properties>
    <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
    <maven.compiler.source>1.8</maven.compiler.source>
    <maven.compiler.target>1.8</maven.compiler.target>
    <spring.version>5.0.2.RELEASE</spring.version>
  </properties>

  <dependencies>
    <dependency>
      <groupId>org.springframework</groupId>
      <artifactId>spring-context</artifactId>
      <version>${spring.version}</version>
    </dependency>

    <dependency>
      <groupId>org.springframework</groupId>
      <artifactId>spring-web</artifactId>
      <version>${spring.version}</version>
    </dependency>

    <dependency>
      <groupId>org.springframework</groupId>
      <artifactId>spring-webmvc</artifactId>
      <version>${spring.version}</version>
    </dependency>

    <dependency>
      <groupId>javax.servlet</groupId>
      <artifactId>servlet-api</artifactId>
      <version>2.5</version>
      <scope>provided</scope>
    </dependency>

    <dependency>
      <groupId>javax.servlet.jsp</groupId>
      <artifactId>jsp-api</artifactId>
      <version>2.0</version>
      <scope>provided</scope>
    </dependency>
  </dependencies>

  <build>
    <finalName>springMVC_demo02_response</finalName>
    <pluginManagement><!-- lock down plugins versions to avoid using Maven defaults (may be moved to parent pom) -->
      <plugins>
        <plugin>
          <artifactId>maven-clean-plugin</artifactId>
          <version>3.1.0</version>
        </plugin>
        <!-- see http://maven.apache.org/ref/current/maven-core/default-bindings.html#Plugin_bindings_for_war_packaging -->
        <plugin>
          <artifactId>maven-resources-plugin</artifactId>
          <version>3.0.2</version>
        </plugin>
        <plugin>
          <artifactId>maven-compiler-plugin</artifactId>
          <version>3.8.0</version>
        </plugin>
        <plugin>
          <artifactId>maven-surefire-plugin</artifactId>
          <version>2.22.1</version>
        </plugin>
        <plugin>
          <artifactId>maven-war-plugin</artifactId>
          <version>3.2.2</version>
        </plugin>
        <plugin>
          <artifactId>maven-install-plugin</artifactId>
          <version>2.5.2</version>
        </plugin>
        <plugin>
          <artifactId>maven-deploy-plugin</artifactId>
          <version>2.8.2</version>
        </plugin>
      </plugins>
    </pluginManagement>
  </build>
</project>

web.xml

<!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>
  <display-name>Archetype Created Web Application</display-name>

  <!--配置前端控制器-->
  <servlet>
    <servlet-name>dispatcherServlet</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>dispatcherServlet</servlet-name>
    <url-pattern>/</url-pattern>
  </servlet-mapping>


  <!--配置解決中文亂碼的過(guò)濾器-->
  <filter>
    <filter-name>characterEncodingFilter</filter-name>
    <filter-class>org.springframework.web.filter.CharacterEncodingFilter</filter-class>
    <init-param>
      <param-name>encoding</param-name>
      <param-value>UTF-8</param-value>
    </init-param>
  </filter>
  <filter-mapping>
    <filter-name>characterEncodingFilter</filter-name>
    <url-pattern>/*</url-pattern>
  </filter-mapping>
</web-app>

springMVC.xml

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
       xmlns:mvc="http://www.springframework.org/schema/mvc"
       xmlns:context="http://www.springframework.org/schema/context"
       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
        http://www.springframework.org/schema/mvc
        http://www.springframework.org/schema/mvc/spring-mvc.xsd
        http://www.springframework.org/schema/context
        http://www.springframework.org/schema/context/spring-context.xsd">

    <!-- 開(kāi)啟注解掃描 -->
    <context:component-scan base-package="com.neuedu"/>


    <!-- 視圖解析器對(duì)象 -->
    <bean id="internalResourceViewResolver" class="org.springframework.web.servlet.view.InternalResourceViewResolver">
        <property name="prefix" value="/WEB-INF/pages/"/>
        <property name="suffix" value=".jsp"/>
    </bean>

    <!-- 開(kāi)啟SpringMVC框架注解的支持 -->
    <mvc:annotation-driven />
</beans>

1. 返回值分類(lèi)

1.1字符串

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 <a href="user/testString" >testString</a>

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實(shí)體類(lèi)User

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package com.neuedu.domain;

import java.io.Serializable;

public class User implements Serializable {
    private String username;
    private String password;
    private Integer age;

    public String getUsername() {
        return username;
    }

    public void setUsername(String username) {
        this.username = username;
    }

    public String getPassword() {
        return password;
    }

    public void setPassword(String password) {
        this.password = password;
    }

    public Integer getAge() {
        return age;
    }

    public void setAge(Integer age) {
        this.age = age;
    }
}

UserController類(lèi)

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package com.neuedu.controller;

import com.neuedu.domain.User;
import org.springframework.stereotype.Controller;
import org.springframework.ui.Model;
import org.springframework.web.bind.annotation.RequestMapping;

@Controller
@RequestMapping("/user")
public class UserController {

    /**
     * 返回String
     * @param model
     * @return
     */
    @RequestMapping("/testString")
    public String testString(Model model){
        System.out.println("testString方法執(zhí)行了...");
        // 模擬從數(shù)據(jù)庫(kù)中查詢(xún)出User對(duì)象
        User user = new User();
        user.setUsername("哈哈");
        user.setPassword("123");
        user.setAge(30);
        // model對(duì)象
        model.addAttribute("user",user);
        return "success";
    }
}

success.jsp

    <h3>執(zhí)行成功</h3>
    ${user.age}
    ${user.password}

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1.2 void

<a href="user/testVoid" >testVoid</a>


    /**
     * 是void
     * 請(qǐng)求轉(zhuǎn)發(fā)一次請(qǐng)求桩砰，不用編寫(xiě)項(xiàng)目的名稱(chēng)
     */
    @RequestMapping("/testVoid")
    public void testVoid(HttpServletRequest request, HttpServletResponse response) throws Exception {
        System.out.println("testVoid方法執(zhí)行了...");
        // 編寫(xiě)請(qǐng)求轉(zhuǎn)發(fā)的程序
        // request.getRequestDispatcher("/WEB-INF/pages/success.jsp").forward(request,response);

        // 重定向
        // response.sendRedirect(request.getContextPath()+"/index.jsp");

        // 設(shè)置中文亂碼
        response.setCharacterEncoding("UTF-8");
        response.setContentType("text/html;charset=UTF-8");

        // 直接會(huì)進(jìn)行響應(yīng)
        response.getWriter().print("你好");

        return;
    }

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1.3 ModelAndView

ModelAndView 是 SpringMVC 為我們提供的一個(gè)對(duì)象，該對(duì)象也可以用作控制器方法的返回值钾怔。
該對(duì)象中有兩個(gè)方法：

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<a href="user/testModelAndView" >testModelAndView</a>


    /**
     * 返回ModelAndView
     * @return
     */
    @RequestMapping("/testModelAndView")
    public ModelAndView testModelAndView(){
        // 創(chuàng)建ModelAndView對(duì)象
        ModelAndView mv = new ModelAndView();
        System.out.println("testModelAndView方法執(zhí)行了...");
        // 模擬從數(shù)據(jù)庫(kù)中查詢(xún)出User對(duì)象
        User user = new User();
        user.setUsername("哈哈");
        user.setPassword("456");
        user.setAge(30);

        // 把user對(duì)象存儲(chǔ)到mv對(duì)象中幔欧，也會(huì)把user對(duì)象存入到request對(duì)象
        mv.addObject("user",user);

        // 跳轉(zhuǎn)到哪個(gè)頁(yè)面
        mv.setViewName("success");

        return mv;
    }

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2 轉(zhuǎn)發(fā)和重定向

2.1 forward

   /**
     * 使用關(guān)鍵字的方式進(jìn)行轉(zhuǎn)發(fā)或者重定向
     * @return
     */
    @RequestMapping("/testForwardOrRedirect")
    public String testForwardOrRedirect(){
        System.out.println("testForwardOrRedirect方法執(zhí)行了...");

        // 請(qǐng)求的轉(zhuǎn)發(fā)
        return "forward:/pages/success.jsp";
    }

需要注意的是微姊，如果用了 formward ：則路徑必須寫(xiě)成實(shí)際視圖 url亭螟，不能寫(xiě)邏輯視圖。
它相當(dāng)于“request.getRequestDispatcher("url").forward(request,response)”法褥。使用請(qǐng)求轉(zhuǎn)發(fā)谒臼，既可以轉(zhuǎn)發(fā)到 jsp朝刊，也可以轉(zhuǎn)發(fā)到其他的控制器方法。

2.2 Redirect 重定向

   /**
     * 使用關(guān)鍵字的方式進(jìn)行轉(zhuǎn)發(fā)或者重定向
     * @return
     */
    @RequestMapping("/testForwardOrRedirect")
    public String testForwardOrRedirect(){
        System.out.println("testForwardOrRedirect方法執(zhí)行了...");
        // 重定向
        return "redirect:/index.jsp";
    }

它相當(dāng)于“response.sendRedirect(url)”屋休。需要注意的是坞古，如果是重定向到 jsp 頁(yè)面，則 jsp 頁(yè)面不能寫(xiě)在 WEB-INF 目錄中劫樟，否則無(wú)法找到痪枫。

3. ResponseBody響應(yīng)json數(shù)據(jù)

作用：
該注解用于將 Controller 的方法返回的對(duì)象，通過(guò) HttpMessageConverter 接口轉(zhuǎn)換為指定格式的數(shù)據(jù)如：json,xml 等叠艳，通過(guò) Response 響應(yīng)給客戶端

需求：
使用@ResponseBody 注解實(shí)現(xiàn)將 controller 方法返回對(duì)象轉(zhuǎn)換為 json 響應(yīng)給客戶端奶陈。

前置知識(shí)點(diǎn)：
Springmvc 默認(rèn)用 MappingJacksonHttpMessageConverter 對(duì) json 數(shù)據(jù)進(jìn)行轉(zhuǎn)換，需要加入jackson 的包附较。

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3.1 準(zhǔn)備

過(guò)濾靜態(tài)資源

導(dǎo)入jquery.js

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response.jsp

    <script src="/js/jquery-3.4.1.js"></script>

    <script>
        // 頁(yè)面加載吃粒，綁定單擊事件
        $(function(){
            $("#btn").click(function(){
                alert("hello btn");
            });
        });

    </script>


<button id="btn">發(fā)送ajax的請(qǐng)求</button>

3.1 使用說(shuō)明

點(diǎn)擊按鈕并沒(méi)有反應(yīng)
原理：web.xml文件中的前端控制器dispatcherServlet會(huì)進(jìn)行攔截
解決：告訴它，哪些靜態(tài)資源不能攔截拒课，在springMVC.xml中設(shè)置

    <!--前端控制器徐勃，哪些靜態(tài)資源不攔截-->
    <mvc:resources location="/css/" mapping="/css/**"/>
    <mvc:resources location="/images/" mapping="/images/**"/>
    <mvc:resources location="/js/" mapping="/js/**"/>

或者可以寫(xiě)成：

<mvc:default-servlet-handler></mvc:default-servlet-handler>

編寫(xiě)原生ajax請(qǐng)求

// 發(fā)送ajax請(qǐng)求
                $.ajax({
                    // 編寫(xiě)json格式，設(shè)置屬性和值
                    url:"user/testAjax",
                    contentType:"application/json;charset=UTF-8",
                    data:'{"username":"hehe","password":"123","age":30}',
                    dataType:"json",
                    type:"post",
                    success:function(data){
                        // data服務(wù)器端響應(yīng)的json的數(shù)據(jù)早像，進(jìn)行解析
                    }
                });

服務(wù)器UserController處理ajax請(qǐng)求數(shù)據(jù)

    /**
     * 模擬異步請(qǐng)求響應(yīng)
     */
    @RequestMapping("/testAjax")
    public void testAjax(@RequestBody String body){
        System.out.println("testAjax方法執(zhí)行了...");
        System.out.println(body);
    }

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3.2 使用示例

向pom.xml導(dǎo)入坐標(biāo)

<dependency>
      <groupId>com.fasterxml.jackson.core</groupId>
      <artifactId>jackson-databind</artifactId>
      <version>2.9.0</version>
    </dependency>
    <dependency>
      <groupId>com.fasterxml.jackson.core</groupId>
      <artifactId>jackson-core</artifactId>
      <version>2.9.0</version>
    </dependency>
    <dependency>
      <groupId>com.fasterxml.jackson.core</groupId>
      <artifactId>jackson-annotations</artifactId>
      <version>2.9.0</version>
    </dependency>

   /**
     * 模擬異步請(qǐng)求響應(yīng)
     */
    @RequestMapping("/testAjax")
    public @ResponseBody User testAjax(@RequestBody User user){
        System.out.println("testAjax方法執(zhí)行了...");
        // 客戶端發(fā)送ajax的請(qǐng)求僻肖，傳的是json字符串，后端把json字符串封裝到user對(duì)象中
        System.out.println(user);

        // 做響應(yīng)卢鹦，模擬查詢(xún)數(shù)據(jù)庫(kù)
        user.setUsername("haha");
        user.setAge(40);
        // 做響應(yīng)
        return user;
    }

// 發(fā)送ajax請(qǐng)求
                $.ajax({
                    // 編寫(xiě)json格式臀脏，設(shè)置屬性和值
                    url:"user/testAjax",
                    contentType:"application/json;charset=UTF-8",
                    data:'{"username":"hehe","password":"123","age":30}',
                    dataType:"json",
                    type:"post",
                    success:function(data){
                        // data服務(wù)器端響應(yīng)的json的數(shù)據(jù)，進(jìn)行解析
                        alert(data);
                        alert(data.username);
                        alert(data.password);
                        alert(data.age);
                    }
                });