概括
HttpMessageConverter，报文信息转换器，用于在HTTP请求和响应之间进行转换的策略接口，即将请求报文转换为Java对象，或将Java对象转换为响应报文。
HttpMessageConverter提供了两个注解和两个类型：@RequestBody，@ResponseBody，RequestEntity，ResponseEntity
环境
<dependencies>
<!-- SpringMVC -->
<dependency>
<groupId>org.springframework</groupId>
<artifactId>spring-webmvc</artifactId>
<version>5.3.1</version>
</dependency>
<!-- 日志 -->
<dependency>
<groupId>ch.qos.logback</groupId>
<artifactId>logback-classic</artifactId>
<version>1.2.3</version>
</dependency>
<!-- ServletAPI -->
<dependency>
<groupId>javax.servlet</groupId>
<artifactId>javax.servlet-api</artifactId>
<version>3.1.0</version>
<scope>provided</scope>
</dependency>
<!-- Spring5和Thymeleaf整合包 -->
<dependency>
<groupId>org.thymeleaf</groupId>
<artifactId>thymeleaf-spring5</artifactId>
<version>3.0.12.RELEASE</version>
</dependency>
</dependencies>
<!--自动扫描包-->
<context:component-scan base-package="com.fly.controller"/>
<!-- 配置Thymeleaf视图解析器 -->
<bean id="viewResolver" class="org.thymeleaf.spring5.view.ThymeleafViewResolver">
<property name="order" value="1"/>
<property name="characterEncoding" value="UTF-8"/>
<property name="templateEngine">
<bean class="org.thymeleaf.spring5.SpringTemplateEngine">
<property name="templateResolver">
<bean class="org.thymeleaf.spring5.templateresolver.SpringResourceTemplateResolver">
<!-- 视图前缀 -->
<property name="prefix" value="/WEB-INF/templates/"/>
<!-- 视图后缀 -->
<property name="suffix" value=".html"/>
<property name="templateMode" value="HTML5"/>
<property name="characterEncoding" value="UTF-8" />
</bean>
</property>
</bean>
</property>
</bean>
<!-- springMVC.xml -->
<mvc:view-controller path="/" view-name="index"/>
<mvc:annotation-driven />
<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>
<init-param>
<param-name>forceResponseEncoding</param-name>
<param-value>true</param-value>
</init-param>
</filter>
<filter-mapping>
<filter-name>CharacterEncodingFilter</filter-name>
<url-pattern>/*</url-pattern>
</filter-mapping>
<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>
<!DOCTYPE html>
<html lang="en" xmlns:th="http://www.thymeleaf.org">
<head>
<meta charset="UTF-8">
<title>首页</title>
</head>
<body>
</body>
</html>
@RequestBody
获取请求体,在控制器方法中用@RequestBody标识一个形参，前请求的请求体就会为当前注解所标识的形参赋值。
<!--index.html-->
<form th:action="@{/testRequestBody}" method="post" enctype="text/plain">
用户名：
<label>
<input name="userName">
</label><br>
密码：
<label>
<input type="password" name="password">
</label>
<input type="submit">
</form>
package com.fly.controller;
import org.springframework.stereotype.Controller;
import org.springframework.web.bind.annotation.RequestBody;
import org.springframework.web.bind.annotation.RequestMapping;
/**
* @author 26414
*/
@Controller
public class HttpController {
@RequestMapping("/testRequestBody")
public String testRequestBody(@RequestBody String requestBody) {
System.out.println("requestBody = " + requestBody);
return "success";
}
}
<!DOCTYPE html>
<html lang="en" xmlns:th="http://www.thymeleaf.org">
<head>
<meta charset="UTF-8">
<title>success</title>
</head>
<body>
<!--success.html-->
<h2>success</h2>
</body>
</html>
RequestEntity
RequestEntity是封装请求报文的一种类型，需要在控制器方法的形参中设置该类型的形参，当前请求的请求报文就会赋值给该形参
/**
*HttpController
*/
@RequestMapping("/testRequestEntity")
public String testRequestEntity(RequestEntity<String> requestEntity) {
System.out.println("requestEntity.getHeaders() = " + requestEntity.getHeaders());
System.out.println("requestEntity.getBody() = " + requestEntity.getBody());
return "success";
}
<!--index.html-->
<form th:action="@{/testRequestEntity}" method="post" enctype="text/plain">
用户名：
<label>
<input name="userName">
</label><br>
密码：
<label>
<input type="password" name="password">
</label>
<input type="submit" value="RequestEntity">
</form>
@ResponseBody
@ResponseBody用于标识一个控制器方法，可以将该方法的返回值直接作为响应报文的响应体响应到浏览器
返回普通类型
/**
*HttpController
*/
@RequestMapping("/testResponseBody")
@ResponseBody
public String testResponseBody() {
return "hhh";
}
<!--index.html-->
<a th:href="@{/testResponseBody}">testResponseBody</a>
返回json
1：导入jackson的依赖
<dependency>
<groupId>com.fasterxml.jackson.core</groupId>
<artifactId>jackson-databind</artifactId>
<version>2.12.1</version>
</dependency>
2：在SpringMVC的核心配置文件中开启mvc的注解驱动
3：使用@ResponseBody注解
4：将Java对象直接作为控制器方法的返回值返回
package com.fly.entity;
/**
* @author 26414
*/
public class Person {
private Integer id;
public Person() {
}
public Person(Integer id, String name, Integer age) {
this.id = id;
this.name = name;
this.age = age;
}
private String name;
private Integer age;
public Integer getId() {
return id;
}
public void setId(Integer id) {
this.id = id;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public Integer getAge() {
return age;
}
public void setAge(Integer age) {
this.age = age;
}
}
/**
*HttpController
*/
@RequestMapping("/testResponseBodyJson")
@ResponseBody
public Person testResponseBodyJson() {
return new Person(1, "张三", 12);
}
<!--index.html-->
<a th:href="@{/testResponseBodyJson}">testResponseBodyJson</a>
@RestController
一个方便的注释，它本身带有@Controller和@ResponseBody注释。 携带该注释的类型被视为控制器，其中@RequestMapping方法默认假设@ResponseBody语义。
ResponseEntity
ResponseEntity用于控制器方法的返回值类型，该控制器方法的返回值就是响应到浏览器的响应报文