SpringMVC @ResponseBody注解 json转换返回406

落日映苍穹つ 2022-06-07 00:59 254阅读 0赞

## 1、描述 ##

SpringMVC通过@RequestMapping注解，自动将对象转换为接送返回。浏览器请求后却返回406错误码。

@Controller
    public class IndexAction { 
        @RequestMapping("/userList")
        public @ResponseBody List<TXUser> userList(String updated_at){
            System.out.println(updated_at);
            TXUser user1=new TXUser();
            user1.setAccount("a1");
            user1.setCode("11");
            user1.setCreated_at(new Date());
            user1.setName("user1");
            TXUser user2=new TXUser();
            user2.setAccount("a2");
            user2.setCode("22");
            user2.setCreated_at(new Date());
            user2.setName("user2");
    
            List<TXUser> userslist=new ArrayList<TXUser>();
            userslist.add(user1);
            userslist.add(user2);
            return userslist;
        }
    
        @RequestMapping("/index")
        public String index(){
            return "index";
        }
    }

## 2、原因 ##

网上找过相关解决方法，但都是修改SpringMVC配置文件添加Converter。我对应修改后均无效。通过debug，发现返回406的原因是因为**org.springframework.web.servlet.mvc.method.annotation.AbstractMessageConverterMethodProcessor**中的**writeWithMessageConverters**方法出现异常。

List<MediaType> requestedMediaTypes = getAcceptableMediaTypes(servletRequest);
    List<MediaType> producibleMediaTypes = getProducibleMediaTypes(servletRequest, returnValueClass);
    Set<MediaType> compatibleMediaTypes = new LinkedHashSet<MediaType>();
    for (MediaType requestedType : requestedMediaTypes) {
        for (MediaType producibleType : producibleMediaTypes) {
            if (requestedType.isCompatibleWith(producibleType)) {
                compatibleMediaTypes.add(getMostSpecificMediaType(requestedType, producibleType));
            }
        }
    }

以上代码中，各个变量的值最后分别为

<table> 
 <thead> 
  <tr> 
   <th>变量</th> 
   <th>值</th> 
  </tr> 
 </thead> 
 <tbody> 
  <tr> 
   <td>requestedMediaTypes</td> 
   <td>[text/html]</td> 
  </tr> 
  <tr> 
   <td>producibleMediaTypes</td> 
   <td>[application/json;charset=UTF-8,application/x-www-form-urlencoded;charset=UTF-8,application/json;charset=UTF-8,application/*+json;charset=UTF-8]</td> 
  </tr> 
  <tr> 
   <td>compatibleMediaTypes</td> 
   <td>[]</td> 
  </tr> 
 </tbody> 
</table>

其中requestedMediaTypes为浏览器向SpringMVC的请求头，由于不匹配SpringMVC对应的请求头，最后返回406。

## 3、解决办法 ##

找到对应原因，通过网络查找资料后，发现修改web.xml文件  
原：

<servlet>
        <servlet-name>spring-mvc</servlet-name>
        <servlet-class>org.springframework.web.servlet.DispatcherServlet</servlet-class>
        <init-param>
            <param-name>contextConfigLocation</param-name>
            <param-value>classpath:spring-mvc.xml</param-value>
        </init-param>
    </servlet>
    <servlet-mapping>
        <servlet-name>spring-mvc</servlet-name>
        <url-pattern>*.htm</url-pattern>
    </servlet-mapping>

修改后：

修改xml后，浏览器再次请求后，正常返回json，不会返回406错误码了。  
此时再次debug，三个变量的值分别为

<table> 
 <thead> 
  <tr> 
   <th>变量</th> 
   <th>值</th> 
  </tr> 
 </thead> 
 <tbody> 
  <tr> 
   <td>requestedMediaTypes</td> 
   <td>[text/html,application/xhtml+xml, image/webp,application/xml;q=0.9,* /*;q=0.8]</td> 
  </tr> 
  <tr> 
   <td>producibleMediaTypes</td> 
   <td>[application/json;charset=UTF-8,application/x-www-form-urlencoded;charset=UTF-8,application/json;charset=UTF-8, application/*+json;charset=UTF-8]</td> 
  </tr> 
  <tr> 
   <td>compatibleMediaTypes</td> 
   <td>[application/json;charset=UTF-8;q=0.8,application/x-www-form-urlencoded;charset=UTF-8;q=0.8,application/*+json;charset=UTF-8;q=0.8]</td> 
  </tr> 
 </tbody> 
</table>