How to interact with json when the return value of the controller method is a simple type?

This article mainly introduces the json data interaction controller method of springmvc. The return value is a simple type, which is very practical. Friends in need can refer to it

When the return value of the controller method is a simple type such as String How to interact with json?

Use @RequestBody

For example, the code is as follows:

@RequestMapping(value="/ceshijson",produces="application/json;charset=UTF-8")
@ResponseBody
public String ceshijson(@RequestBody String channelId) throws IOException{

 return channelId;

If the code is the above situation, the front desk sends json When using @RequestBody, it should be written like this (there are many ways to write it, just use it)

function channel(){
   //先获取选中的值
   var channelId = $("#channelId option:selected").val();
   //来判断发送的链接
   if(channelId ==2){


   $.ajax({
     url:"ceshijson",
     type:"post",
     dataType:'json',
     contentType:'application/json;charset=utf-8',
     data:JSON.stringify({'channelId':channelId}),
     success:function(data){
      alert(data.channelId);
     },
     error:function(XMLHttpRequest, textStatus, errorThrown){ 
     alert("Error") 
     alert(XMLHttpRequest.status); 
     alert(XMLHttpRequest.readyState); 
     alert(textStatus); 
     }
   });
   }
  }

Special attention needs to be paid here: As emphasized in the previous article, when @RequestBody is used, it requires String channelId to receive data as json String . That is, if data is written like this: data:{'channelId':channelId}, it is wrong. Because this is jsonobject form.

If you don’t want to use the JSON.stringify() function, then manually splice the strings yourself:

data:'{"channelId":'+channelId+'}'

Also note that channelId is in double quotes and cannot be written as Single quotes because this is a json syntax rule. If you change it to single quotes, that is,

**wrong way of writing

data:"{'channelId':"+channelId+"}"

, although it can be passed to the background, the data returned from the background will be undefined. That is, key must be surrounded by double quotes.

Do not use @RequestBody

 @RequestMapping(value="/ceshijson",produces="application/json;charset=UTF-8")
 @ResponseBody
 public String ceshijson(String channelId) throws IOException{
  Map<String,Object> map = new HashMap<String,Object>();
   map.put("channelId", channelId);
   ObjectMapper mapper = new ObjectMapper();
   channelId = mapper.writeValueAsString(map);
  return channelId;
 }

Front-end code

$.ajax({
   url:"ceshijson",
   type:"post",
   dataType:'json',
   //contentType:'application/json;charset=utf-8',
   data:"channelId="+channelId,
   success:function(data){
    alert(data);
   },
   error:function(XMLHttpRequest, textStatus, errorThrown){ 
     alert("Error") 
     alert(XMLHttpRequest.status); 
     alert(XMLHttpRequest.readyState); 
     alert(textStatus); 
    }
});

This method uses writeValueAsString in ObjectMapper to convert Java objects into json strings.

Summary: This method actually does not have much practical meaning, because data is generally not received in this way. Just understand!

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