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，HttpMessageConverter提供了两个注解和两个类型：@RequestBody ,@ResponseBody,RequestEntity,ResponseEntity

1、@RequestBody

@RequestBody可以获取请求体，需要在控制器方法设置一个形参，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

输出结果：
username=admin&password=123456

2、RequestEntity

RequestEntity封装请求实体的一种类型，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()获取请求体信息输出结果：
请求头:[host:”localhost:8080″, connection:”keep-alive”, content-length:”82″, cache-control:”max-age=0″, sec-ch-ua:”” Not;A Brand”;v=”99″, “Google Chrome”;v=”97″, “Chromium”;v=”97″”, sec-ch-ua-mobile:”?0″, sec-ch-ua-platform:””Windows””, upgrade-insecure-requests:”1″, origin:”http://localhost:8080″, user-agent:”Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/97.0.4692.99 Safari/537.36″, accept:”text/html,application/xhtml+xml,application/xml;q=0.9,image/avif,image/webp,image/apng,/;q=0.8,application/signed-exchange;v=b3;q=0.9″, sec-fetch-site:”same-origin”, sec-fetch-mode:”navigate”, sec-fetch-user:”?1″, sec-fetch-dest:”document”, referer:”http://localhost:8080/springMVC/”, accept-encoding:”gzip, deflate, br”, accept-language:”zh-CN,zh;q=0.9″, cookie:”JSESSIONID=EF6915CD7E434F56D482A5C9667CF03A”, Content-Type:”application/x-www-form-urlencoded;charset=UTF-8″]
请求体:username=admin&password=123

3、ResponseBody

@ResponseBody用于标识一个控制器方法，可以将方法的返回值直接作为响应报文的响应体响应到浏览器

    @RequestMapping(value = "/testResponseBody")
    @ResponseBody
    public String testResponseBody() {
        return "success";
    }

结果：浏览器页面显示success

4、SpringMVC处理json

@ResponseBody 处理json的步骤
a>导入jackson依赖

 <!--jackson-->
        <dependency>
            <groupId>com.fasterxml.jackson.core</groupId>
            <artifactId>jackson-databind</artifactId>
            <version>2.12.1</version>
        </dependency>

b>在SpringMVC的核心配置文件中开启mvc注解的驱动，此时在HandelerAdapter中会自动装配一个消息转换器，MappingJackon2HttpMessageConverter,可以响应到浏览器的java对象转换为json格式的字符串

<!--开启SpringMVC注解驱动-->
    <mvc:annotation-driven />

c>在处理器方法上使用@ResponseBody注解进行标识

d>将Java对象直接作为控制器方法的返回值返回，就会自动转换为json格式的字符串

    @RequestMapping(value = "/testResponseUser")
    @ResponseBody
    public User testResponseUser() {
        return new User(1001,"admin","123456",23,"男");
    }

浏览器页面中展示的结果 {“id”:1001,”age”:23,”sex”:”男”,”password”:”123456″,”username”:”admin”}

5、SpringMVC处理ajax

a>请求超链接

<div id="app">
    <a th:href="@{/testAxios}">SpringMVC处理ajax</a>
</div>

通过vue和axios处理点击事件

<script type="text/javascript" th:src="@{/static/js/vue.js}"></script>
<script type="text/javascript" th:src="@{/static/js/axios.min.js}"></script>
<script type="text/javascript">
    new Vue({
        el:"#app",
        methods:{
            testAxios:function (event) {
                axios({
                    method:"post",
                    url:event.target.href,
                    params:{
                        uesername:"admin",
                        password:"123456",
                    }
                }).then(function (response) {
                        alert(response.data);
                });
                    event.preventDefault()
            }
        }
    });
</script>

c>控制器方法

    @RequestMapping(value = "/testAxios")
    @ResponseBody
    public String testAxios(String username,String password) {
        System.out.println("username"+","+password);
        return "hello.axios";
    }