<dependency>
      <groupId>com.fasterxml.jackson.core</groupId>
      <artifactId>jackson-databind</artifactId>
      <version>2.9.8</version>
    </dependency>

function responseKV(){
  $.ajax({
    type:"post",
    url:'${pageContext.request.contextPath }/responseKV',
    //輸入是key/value時，默認就指定好了contentType了，不需要再指定了
    //contentType:'application/json;charset=utf-8',
    //data為key/value形式
    data:'name=json測試&price=999',
    success:function(data){
      alert(data);
    }
  });
}

// 輸入是key/value，輸出是json
// @ResponseBody 將返回值轉成json串響應給前臺
@RequestMapping("/responseKV")
@ResponseBody
public Item responseKV(Item item) {
  return item;
}

function requestJson(){
  $.ajax({
    type:"post",
    url:'${pageContext.request.contextPath }/requestJson',
    //輸入是json是 ，需要指定contentType為application/json
    contentType:'application/json;charset=utf-8',
    data:'{"name":"json測試","price":999}',
    success:function(data){
      alert(data.name);
    }
  });
}

@Controller
public class JsonController {
  // 輸入是json，輸出是json
  // @RequestBody 將請求的json串轉成java對象
  // @ResponseBody 將返回值轉成json串響應給前臺
  @RequestMapping("/requestJson")
  @ResponseBody
  public Item requestJson(@RequestBody Item item) {
    return item;
  }
}