SpringMVC：HttpMessageConverter

HttpMessageConverter

报文信息转换器。

将请求报文转换成java对象，将java对象转换成响应报文。

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

@RequestBody

<form th:action="@{/testRequest}" method="post">
    <input type="text" name="username"><br>
    <input type="text" name="password"><br>
    <input type="submit" value="提交"><br>
</form>

@RequestMapping("/testRequest")
public String testRequest(@RequestBody String requestBody){
    System.out.println(requestBody);
    return "success";
}
//打印结果为username=admin&password=admin

RequestEntity

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

@RequestMapping("/testRequestEntity")
public String testRequestEntity(RequestEntity<String> requestEntity){
    System.out.println(requestEntity.getHeaders());
    System.out.println(requestEntity.getBody());
    return "success";
}
//打印结果为[host:"localhost:8080", connection:"keep-alive", content-length:"25", cache-control:"max-age=0", sec-ch-ua:""Google Chrome";v="95", "Chromium";v="95", ";Not A Brand";v="99"", 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/95.0.4638.54 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_4/", accept-encoding:"gzip, deflate, br", accept-language:"zh-CN,zh;q=0.9", cookie:"JSESSIONID=265D329EF9F022E755E85C6065DC7E4F", Content-Type:"application/x-www-form-urlencoded;charset=UTF-8"]
//另一结果为username=123&password=123

@ResponseBody

@RequestMapping("/testResponseBody")
@ResponseBody
public String testResponseBody(){
    return "hello world";
}
//结果为：在浏览器中的一个新页面上打印hello world

@ResponseBody处理json的步骤：

a>导入jackson的依赖

<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 />

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

浏览器的页面中展示的结果：

{"id":1001,"username":"admin","password":"123456","age":23,"sex":"男"}

处理ajax

使用Vue响应ajax

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

<script>
    var vue = new Vue({
        el:"#div",
        methods:{
            //点击事件
            testAjax:function (event){
                axios({
                    //请求方法
                    method:"post",
                    //请求url
                    url:event.target.href,
                    //请求参数
                    params:{
                        username:"admin",
                        password:"admin"
                    }
                    //回调函数——指请求成功或是失败执行的函数。
                }).then(function (response){
                    alert(response.data);
                })
                //用来取消event的默认动作。
                event.preventDefault();

            }
        }
    });
</script>

@RestController

@RestController注解是springMVC提供的一个复合注解，标识在控制器的类上，就相当于为类添加了@Controller注解，并且为其中的每个方法添加了@ResponseBody注解

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

1、文件下载

使用ResponseEntity实现下载文件的功能

@RequestMapping("/testDown")
public ResponseEntity<byte[]> testResponseEntity(HttpSession session) throws IOException {
    //获取ServletContext对象
    ServletContext servletContext = session.getServletContext();
    //获取服务器中文件的真实路径
    String realPath = servletContext.getRealPath("/static/img/1.jpg");
    //创建输入流
    InputStream is = new FileInputStream(realPath);
    //创建字节数组
    byte[] bytes = new byte[is.available()];
    //将流读到字节数组中
    is.read(bytes);
    //创建HttpHeaders对象设置响应头信息
    MultiValueMap<String, String> headers = new HttpHeaders();
    //设置要下载方式以及下载文件的名字
    headers.add("Content-Disposition", "attachment;filename=1.jpg");
    //设置响应状态码
    HttpStatus statusCode = HttpStatus.OK;
    //创建ResponseEntity对象
    ResponseEntity<byte[]> responseEntity = new ResponseEntity<>(bytes, headers, statusCode);
    //关闭输入流
    is.close();
    return responseEntity;
}

标签：HttpMessageConverter,SpringMVC,ResponseBody,sec,ResponseEntity,注解,new,admin
来源： https://www.cnblogs.com/Boerk/p/15869542.html