泛型--->Result返回结果封装

controller的返回结果一般有两种：

    1.Rest API JSON 输出

    2.页面

目的：编写优雅的代码

实现：通过泛型对返回结果进行封装

代码如下：

一.控制层

 /**
      * 获取用户成功
      * @return
      */
     @RequestMapping("/getUser")
     @ResponseBody
     public Result<User> getUser(@RequestParam("id") int id){
         User user = userService.getUserById(id);
         System.out.println(user.toString());

         return Result.success(user);
     }

返回结果：{"code":0,"message":"SUCCESS","data":{"id":1,"name":"斗战胜佛"}}

 /**
      * 获取用户失败
      * @param id
      * @return
      */
     @RequestMapping("/getUserFailed")
     @ResponseBody
     public Result<CodeMsg> getUserFailed(@RequestParam("id") int id){
         User user = userService.getUserById(id);
         System.out.println(user.toString());

         return Result.error(CodeMsg.SERVER_ERROR);
     }

返回结果：{"code":500100,"message":"服务端异常","data":null}

二：Result类

 public class Result<T> {

     private int code;
     private String message;
     private T data;

     /**
      * 成功时调用
      * @param data
      * @param <T>
      * @return
      */
     public static <T> Result<T> success(T data){
         return new Result<T>(data);
     }

     /**
      * 失败时调用
      * @param codeMsg
      * @param <T>
      * @return
      */
     public static <T> Result error(CodeMsg codeMsg){
         return new Result<T>(codeMsg);
     }

     /**
      * 构造方法私有化，不允许外部new Result
      * @param data
      */
     private Result(T data){
         this.code = 0;
         this.message = "SUCCESS";
         this.data = data;
     }

     /**
      * 构造方法私有化，不允许外部new Result
      * @param codeMsg
      */
     private Result(CodeMsg codeMsg){
         if (null == codeMsg) {
             return;
         }
         this.code = codeMsg.getCode();
         this.message = codeMsg.getMessage();
     }

     public int getCode() {
         return code;
     }

     public void setCode(int code) {
         this.code = code;
     }

     public String getMessage() {
         return message;
     }

     public void setMessage(String message) {
         this.message = message;
     }

     public T getData() {
         return data;
     }

     public void setData(T data) {
         this.data = data;
     }
 }

三：CodeMsg类

 public class CodeMsg {

      private int code;
      private String message;

     /**
      * //通用模块异常 5001XX
      */
     public static CodeMsg SUCCESS = new CodeMsg(0,"SUCCESS");
      public static CodeMsg SERVER_ERROR = new CodeMsg(500100,"服务端异常");

      //登陆模块异常 5002XX
     //商品模块异常 5003XX
     //订单模块异常 5004XX
     //秒杀模块异常 5005XX

     private CodeMsg(int code, String message) {
         this.code = code;
         this.message = message;
     }

     public int getCode() {
         return code;
     }

     public String getMessage() {
         return message;
     }
 }