HttpMessageConverter

HttpMessageConverter:报文信息转换器，将请求报文转换为Java对象，或将Java对象转换为响应报文。它提供了两个注解和两个类型：
@RequestBody, @ResponseBody, RequestEntity, ResponseEntity(响应用的较多)

准备

创建模块并完成配置文件编写

success.html

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8" xmlns:th="http://www.thymeleaf.org">
    <title>Title</title>
</head>
<body>
success
</body>
</html>

web.xml

<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">
  <!--配置编码过滤器-->
  <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>
    <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>
  <!--配置请求方式put和delete的hiddenHttpMethodFilter-->
  <filter>
    <filter-name>HiddenHttpMethodFilter</filter-name>
    <filter-class>org.springframework.web.filter.HiddenHttpMethodFilter</filter-class>
  </filter>
  <filter-mapping>
    <filter-name>HiddenHttpMethodFilter</filter-name>
    <url-pattern>/*</url-pattern>
  </filter-mapping>
  <!--配置springMVC的前端控制器DispatcherServlet-->
  <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>
    <!--将前端控制器的时间提前到服务器启动时-->
    <load-on-startup>1</load-on-startup>
  </servlet>
  <servlet-mapping>
    <servlet-name>DispatcherServlet</servlet-name>
    <url-pattern>/</url-pattern>
  </servlet-mapping>
</web-app>

SpringMVC.xml

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
       xmlns:context="http://www.springframework.org/schema/context"
       xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
       xsi:schemaLocation="
       http://www.springframework.org/schema/context
       http://www.springframework.org/schema/context/spring-context.xsd
       http://www.springframework.org/schema/beans
       http://www.springframework.org/schema/beans/spring-beans.xsd">

    <!--开启扫描组件-->
    <context:component-scan base-package="com.louis"></context:component-scan>
    <!--配值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">
                        <property name="prefix" value="/WEB-INF/templates/"/>
                        <property name="suffix" value=".html"/>
                        <property name="templateMode" value="HTML5"/>
                        <property name="characterEncoding" value="UTF-8"/>
                    </bean>
                </property>
            </bean>
        </property>
    </bean>
</beans>

@RequestBody

@RequestBody可以获取请求体，需要在控制方法设置一个形参，使用@RequestBody进行标识，当前请求的请求体就会为当前注解所标识的形参赋值(只求POST请求方式才会有请求体)

HttpController

@Controller
public class HttpController {
    @RequestMapping("/testRequestBody")
    public String testRequestBody(@RequestBody String requestBody){
        System.out.println("requestBody = " + requestBody);
        return "success";
    }
}

index.html

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8" xmlns:th="http://www.thymeleaf.org">
    <title>首页</title>
</head>
<body>
<h3>首页</h3>
<form th:action="@{/testRequestBody}" method="post">
    <input type="text" name="username">
    <input type="text" name="password">
    <input type="submit" value="测试@RequestBody">
</form>
</body>
</html>

测试

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控制台

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RequestEntity

RequestEntity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，可以通过getHeaders()获取请求头信息，通过getBody()获取请求体信息。

index.html

<form th:action="@{/testRequestEntity}" method="post">
    <input type="text" name="username">
    <input type="text" name="password">
    <input type="submit" value="测试RequestEntity">
</form>

HttpController

@RequestMapping("/testRequestEntity")
public String testRequestEntity(RequestEntity<String> requestEntity){
    //当前的RequestEntity表示整个请求报文的信息
    System.out.println("获取请求头:" + requestEntity.getHeaders());
    System.out.println("获取请求体:" + requestEntity.getBody());
    return "success";
}

测试

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后端

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@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。将数据响应到浏览器的方法有如下两种。

①直接使用ServletAPI

index.html

<a th:href="@{/testResponse}">通过servletAPI的response对象响应浏览器数据</a>

HttpController

@RequestMapping("/testResponse")
public void testResponse(HttpServletResponse response) throws IOException {
    response.getWriter().write("hello response");
}

测试

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②使用@ResponseBody

为了便于区分将success中的内容修改为如下

<h3>success</h3>

index.html

<a th:href="@{/testResponseBody}">通过@ResponseBody响应浏览器数据</a>

HttpController

@RequestMapping("/testResponseBody")
@ResponseBody
public String testResponseBody(){
    /*加上@ResponseBody之后返回的就不再是视图名称，而是当前响应的响应体*/
    return "success";
}