SpringMVC如何操作请求和响应报文的

前言

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

零、请求和响应报文小知识

# 一、@RequestBody
作用:该注解修饰的参数与请求体形成映射关系，并将请求体赋值给该形参

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

打印内容

RequestBody = username=admin&password=123456

二、RequestEntity

作用:该注解修饰的形参与请求报文请求映射关系，并将请求报文赋值给修饰的形参,就可以获取请求报文的内容

@RequestMapping("/testRequestEntity")
    public String testRequestEntity(RequestEntity<String> request){
        HttpHeaders headers = request.getHeaders();
        HttpMethod method = request.getMethod();
        Type type = request.getType();
        URI url = request.getUrl();
        String body = request.getBody();
        System.out.println("header = "+ headers + "\n method = "
        + method + "\n type = " + type + "\n URI = " + url
        + "\n body = " + body);
        return "success";
    }

打印内容

header = [host:"localhost:8080", connection:"keep-alive", content-length:"29", cache-control:"max-age=0", sec-ch-ua:"" Not A;Brand";v="99", "Chromium";v="100", "Google Chrome";v="100"", 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/100.0.4896.127 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_demo5/", accept-encoding:"gzip, deflate, br", accept-language:"zh-CN,zh;q=0.9", cookie:"Idea-aafc8dba=ffa8b7f0-935d-4c1b-ad7c-93ba1d53922c", Content-Type:"application/x-www-form-urlencoded;charset=UTF-8"]
 method = POST
 type = class java.lang.String
 URI = http://localhost:8080/springMVC_demo5/testRequestEntity
 body = username=admin&password=admin

三、 @ResponseBody(重点)

作用:将控制器方法的返回值响应到浏览器

@RequestMapping("/testResponseBody")
    @ResponseBody
    public String testResponseBody(){
        return "<font color='red'>success</font>";
    }

执行结果

原生servlet实现

@RequestMapping("/testResponseServletApi")
    public String testResponseServletApi(HttpServletResponse response) throws IOException {
        // 设置响应编码
        response.setContentType("text/html;character=UTF-8");
        response.getWriter().write("是你");
        return null;
    }

四、@RestController注解

该注解属于@ResponseBody和@Controller的复合注解,修饰类,为该控制器层下的每个方法添加@ResponseBody注解

五、ResponseEntity

六、 扩展知识

6.1 设置响应编码的方式

1. response.setContentType(“text/html; charset=UTF-8”);

第一种不仅发送到浏览器的内容会使用UTF-8编码，而且还通知浏览器使用UTF-8编码方式进行显示。所以总能正常显示中文

即：服务端用utf编码，并且告诉浏览器用utf-8的编码显示

2. response.setCharacterEncoding(“UTF-8”);

第二种仅仅是发送的浏览器的内容是UTF-8编码的，至于浏览器是用哪种编码方式显示不管。 所以当浏览器的显示编码方式不是UTF-8的时候，就会看到乱码，需要手动再进行一次设置。

6.2 SpringMVC处理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. 开启springMVC注解驱动

在SpringMVC的核心配置文件中开启mvc的注解驱动，此时在HandlerAdaptor中会自动装配一个消息转换器：MappingJackson2HttpMessageConverter，可以将响应到浏览器的Java对象转换为Json格式的字符串

<mvc:annotation-driven />

返回的java对象则自动会转为json对象

@RequestMapping("/testResponseUser")
    public User testResponseUser(User user){
        User user1 = new User("张三", "123456");
        return user1;
    }

打印内容

{"name":"张三","password":"123456"}

6.3 SpringMVC处理ajax

1. 请求超链接：

<div id="app">
	<a th:href="@{/testAjax}" @click="testAjax">testAjax</a><br>
</div>

2. 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">
    var vue = new Vue({
        el:"#app",
        methods:{
            testAjax:function (event) {
                axios({
                    method:"post",
                    url:event.target.href,
                    params:{
                        username:"admin",
                        password:"123456"
                    }
                }).then(function (response) {
                    alert(response.data);
                });
                event.preventDefault();
            }
        }
    });
</script>

3. 控制器方法：

@RequestMapping("/testAjax")
@ResponseBody
public String testAjax(String username, String password){
    System.out.println("username:"+username+",password:"+password);
    return "hello,ajax";
}

打印内容

username = admin password = 123456

总结

好好努力，加油陌生人!!!