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){
     **需要注意地方 start**
     var schoolBannerInfo = {
      "img": channelId,
      "title": channelId,
      "info": channelId,
      "channelId": channelId
     };
     **需要注意地方 end**

      $.ajax({
         url:"ceshijson",
         type:"post",
         dataType:'json',
         **需要注意地方 start**
         contentType:'application/json;charset=utf-8',
         data:JSON.stringify(schoolBannerInfo),
         **需要注意地方 end**
         success:function(data){
            alert(data);
         },
         error:function(XMLHttpRequest, textStatus, errorThrown){ 
          alert("Error") 
          alert(XMLHttpRequest.status); 
          alert(XMLHttpRequest.readyState); 
          alert(textStatus); 
          }
      });
     }
   }

public class SchoolBannerInfo {
  private Integer id;
  private Date createTime;
  private String img;
  private String title;
  private String info;
  private Integer seq;
  private Integer schoolId;
  private String type;
  private boolean enable;
  private String link;
  private String channelId;
}

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