SpringMVC篇-处理 JSON：使用HttpMessageConverter

太过爱你忘了你带给我的痛 2023-10-04 11:45 6阅读 0赞

## 处理 JSON：使用HttpMessageConverter ##

使用示例:

*  加入 jar 包

> 其中。spring版本越高需要配置的json jar包的版本号就越高，否则会报错

![在这里插入图片描述][20210424002146231.png]

*  编写目标方法，使其返回 JSON 对应的对象或集合
 *  在方法上添加 @ResponseBody 注解

@ResponseBody
        @RequestMapping("/testJson")
        public Collection<Employee> testJson(){
        
            return employeeDao.getAll();
        }

<a href="testJson" id="testJson">Test Json</a>
    <script type="text/javascript" src="scripts/jquery-1.9.1.min.js"></script>
        <script type="text/javascript">
            $(function(){
        
                $("#testJson").click(function(){
        
                    var url = this.href;
                    var args = {
        };
                    $.post(url, args, function(data){
        
                        for(var i = 0; i < data.length; i++){
        
                            var id = data[i].id;
                            var lastName = data[i].lastName;
    
                            alert(id + ": " + lastName);
                        }
                    });
                    return false;
                });
            })
        </script>

### HttpMessageConverter`<T>` ###

> HttpMessageConverter`<t>`是 Spring3.0 新添加的一个接 口，负责将请求信息转换为一个对象（类型为 T），将对象（ 类型为 T）输出为响应信息

原理图解

![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzQ1NDA4Mzkw_size_16_color_FFFFFF_t_70]

**HttpMessageConverter`<T>`实现类**

![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzQ1NDA4Mzkw_size_16_color_FFFFFF_t_70 1]

> DispatcherServlet 默认装配 RequestMappingHandlerAdapter ，而 RequestMappingHandlerAdapter 默认装配如下 HttpMessageConverter
> 
> 前提： 加入 jackson jar 包后， RequestMappingHandlerAdapter 装配的 HttpMessageConverter

代码示例:

<br><br>
        <form action="testHttpMessageConverter" method="POST">
            File: <input type="file" name="file"/>
            Desc: <input type="text" name="desc"/>
            <input type="submit" value="Submit"/>
        </form>
    
        <br><br>
    
        <a href="testResponseEntity">Test ResponseEntity</a>

handler.java

@RequestMapping("/testResponseEntity")
        public ResponseEntity<byte[]> testResponseEntity(HttpSession session) throws IOException {
        
            byte [] body = null;
            ServletContext servletContext = session.getServletContext();
            System.out.println(servletContext.getContextPath());
            InputStream in = servletContext.getResourceAsStream("/files/abc.txt");
            body = new byte[in.available()];
            in.read(body);
    
            HttpHeaders headers = new HttpHeaders();
            headers.add("Content-Disposition", "attachment;filename=abc.txt");
    
            HttpStatus statusCode = HttpStatus.OK;
    
            ResponseEntity<byte[]> response = new ResponseEntity<byte[]>(body, headers, statusCode);
            return response;
        }
    
        @ResponseBody
        @RequestMapping("/testHttpMessageConverter")
        public String testHttpMessageConverter(@RequestBody String body){
        
            System.out.println(body);
            return "helloworld! " + new Date();
        }

[20210424002146231.png]: https://img-blog.csdnimg.cn/20210424002146231.png
[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzQ1NDA4Mzkw_size_16_color_FFFFFF_t_70]: https://img-blog.csdnimg.cn/20210424002134981.png?x-oss-process=image/watermark,type_ZmFuZ3poZW5naGVpdGk,shadow_10,text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzQ1NDA4Mzkw,size_16,color_FFFFFF,t_70
[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzQ1NDA4Mzkw_size_16_color_FFFFFF_t_70 1]: https://img-blog.csdnimg.cn/2021042400212422.png?x-oss-process=image/watermark,type_ZmFuZ3poZW5naGVpdGk,shadow_10,text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzQ1NDA4Mzkw,size_16,color_FFFFFF,t_70