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The pitfalls I have recently stepped on in my work will be used for the results.Result<T>Encapsulation, but I stepped on two big pits of FastJson and construction method. Share it, please be careful not to step on the same pit.

1. Test code

1. CreatedResult<String>Object, serialized to JSON string
2. Deserialize JSON strings toResult<String>Object

   public static void main(String[] args) {
            // Create an object
            Result<String> result = new Result<String>()
                    .setRet(-1)
                    .setData(null)
                    .setError(new (404).addErrorDetail("id", 9, ""));
            // Serialize the object into a JSON string
            String resultJson = (result,
                    ,
                    );
            (resultJson);
    ​
            // Deserialization
            Result<String> resultFromJson = (resultJson, new TypeReference<Result<String>>() {
            });
            (resultFromJson);
     }

   Serialized JSON string

   {
   	"data":null,
   	"error":{
   		"code":404,
   		"details":[
   			{
   				"data":9,
   				"field":"id",
   				"msg":""
   			}
   		]
   	},
   	"ret":-1
   }

   It has to do with the construction method.creatorConstructorDetermined asError(int code)This construction method, and this construction method is onlyint codeThis parameter is created in deserializationWhen, that's itcodeAssignment of fields without deserializationdetailsField.

Solution

• Adding construction methodError(int code, List<ErrorDetail> details)
• Result<T>Adding the parameterless construction method
  At this point, the problem is solved.

summary

• JSON deserialization is closely related to constructing methods. It is recommended that each class provide parameterless constructing methods.
• If a certain class is not designed to provide a parameterless construction method, special attention should be paid to the above two issues. It is recommended to provide a full-parameter construction method.

Related Class Definitions

Correct Result<T>

import ;
 import ;

 import ;
 import ;


 @Data
 @Accessors(chain = true)
 public class Result<T> {

     /**
      * ret >= 0 success;
      * ret < 0 error;
      */
     private int ret;

     private T data;

     private Error error;

     @Data
     @Accessors(chain = true)
     public static class Error {

         private int code;

         private List<ErrorDetail> details;

         public Error(int code) {
              = code;
              = new ArrayList<>();
         }

         /**
          * Pay special attention to the modification of the construction method, and do not put it before the previous construction method, otherwise it will cause FastJson reverse-sequence listing problems.
          * <p>
          * public Error(CmnCode code) {
          * = ();
          * = new ArrayList<>();
          * }
          */

         public Error(int code, List<ErrorDetail> details) {
              = code;
             if (null == details) {
                  = new ArrayList<>();
             } else {
                  = details;
             }
         }

         public Error addErrorDetail(String msg) {
             (new ()
                     .setMsg(msg));
             return this;
         }

         public Error addErrorDetail(String field, String msg) {
             (new ()
                     .setField(field)
                     .setMsg(msg));
             return this;
         }

         public Error addErrorDetail(Object data, String msg) {
             (new ()
                     .setData(data)
                     .setMsg(msg));
             return this;
         }

         public Error addErrorDetail(String field, Object data, String msg) {
             (new ()
                     .setField(field)
                     .setData(data)
                     .setMsg(msg));
             return this;
         }
     }

     @Data
     @Accessors(chain = true)
     public static class ErrorDetail {

         /**
          * error field;
          */
         private String field;

         /**
          * error field value;
          */
         private Object data;

         /**
          * error field message;
          */
         private String msg;
     }
 }

CmnCode Enumeration

import ;


public enum CmnCode implements Serializable {

    /**
     * ok
     */
    OK(200),

    BAD_REQUEST(400),
    UNAUTHORIZED(401),
    FORBIDDEN(403),
    NOT_FOUND(404),
    METHOD_NOT_ALLOWED(405),
    NOT_ACCEPTABLE(406),
    CONFLICT(409),
    PRECONDITION_FAILED(412),
    UNSUPPORTED_MEDIA_TYPE(415),
    PROTOCOL_NOT_MATCH(444),
    INTERNAL_ERROR(500),
    GATEWAY_ERROR(502),
    SERVICE_UNAVAILABLE(503),
    GATEWAY_TIMEOUT(504);

    private int code;

    CmnCode(int code) {
         = code;
    }

    public static CmnCode fromHttpStatus(int httpStatus) {
        for (CmnCode cmnCode : values()) {
            if (() == httpStatus) {
                return cmnCode;
            }
        }
        return INTERNAL_ERROR;
    }

    public int getCode() {
        return code;
    }

    public CmnCode setCode(int code) {
         = code;
        return this;
    }
}

Result<T> that caused the problem

@Data
@Accessors(chain = true)
public class Result<T> {

    /**
     * ret >= 0 success;
     * ret < 0  error;
     */
    private int ret;
    
    private T data;

    private Error error;

    @Data
    @Accessors(chain = true)
    public static class Error {

        private int code;

        private List<ErrorDetail> details;

        public Error(CmnCode cmnCode) {
             = ();
             = new ArrayList<>();
        }

        public Error(int code) {
             = code;
             = new ArrayList<>();
        }
    }
}