Java : Convert Object consisting enum to Json Object

问题:

I am using org.json library to convert Object to Json format. Kindly check the below code snippet.

public enum JobStatus implements Serializable{      INCOMPLETE,      INPROGRESS,      ABORTED,      COMPLETED }  public class Job implements Serializable {     private string id;     private JobStatus status;     ... }  ...  // Create Job Object Job job = new Job("12345", JobStatus.INPROGRESS);  // Convert and print in JSON format System.out.println(new JSONObject(job).toString()); 

It shows the output like this :

 {"id":"12345", "status" : {}} 

It shows blank and adds Curly bases. What does it mean? Is anybody gone through this problem?

回答1:

First of all I highly recommend do not use this library (org.json), this is very old and unsupported (as i know) library. I suggest Jackson or Gson.

But if you really need JSONObject, you can add getter into enum:

 public enum JobStatus implements Serializable{     INCOMPLETE,     INPROGRESS,     ABORTED,     COMPLETED;      public String getStatus() {         return this.name();     } } 

result of serialization:

{"id":"12345","status":{"status":"INPROGRESS"}} 

As I know, JSONObject don't support correct serialization of enums which not have any additional data inside.

回答2:

It seems JSONObject doesn't support enums. You could alter your Job class to add a getter like this:

public String getStatus() {     return status.name(); } 

then, invoking new JSONObject(job).toString() produces:

{"id":"12345","status":"INPROGRESS"} 

回答3:

ObjectMapper mapper= new ObjectMapper();  new JSONObject(mapper.writeValueAsString(job)); 

would do the trick. Now Enums and DateTime types looks normal and is converted properly in json objects.

I came to this page as a person seeking answer and my research helped me to answer this question.

回答4:

for me, i made an interface that shuold be implemented by any enum i will have to use in Json, this interface forces the enum to know the proper enum itself from a value, and also it should return a value ... so every enum.CONSTANT is mapped to a value of any type (weather a number or a String)

so when i want to put this enum in a Json Object, i ask the enum.CONSTANT to give me it's value, and when i have this value (from Json), i can request from the enum to give me the proper enum.CONSTANT mapped to this value

the interface is as follows (you can copy it as it is) :

/**  *   * this interface is intended for {@code enums} (or similar classes that needs  * to be identified by a value) who are based on a value for each constant,  * where it has the utility methods to identify the type ({@code enum} constant)  * based on the value passed, and can declare it's value in the interface as  * well  *   * @param <T>  *            the type of the constants (pass the {@code enum} as a type)  * @param <V>  *            the type of the value which identifies this constant  */ public interface Valueable<T extends Valueable<T, V>, V> {      /**      * get the Type based on the passed value      *       * @param value      *            the value that identifies the Type      * @return the Type      */     T getType(V value);      /**      * get the value that identifies this type      *       * @return a value that can be used later in {@link #getType(Object)}      */     V getValue(); } 

now here is an example for a small enum implementing this interface:

public enum AreaType implements Valueable<AreaType, Integer> {     NONE(0),     AREA(1),     NEIGHBORHOOD(2);      private int value;      AreaType(int value) {         this.value = value;     }      @Override     public AreaType getType(Integer value) {          if(value == null){             // assume this is the default             return NONE;         }          for(AreaType a : values()){             if(a.value == value){ // or you can use value.equals(a.value)                 return a;             }         }         // assume this is the default         return NONE;     }      @Override     public Integer getValue() {         return value;     }  } 

to save this enum in a Json :

AreaType areaType = ...; jsonObject.put(TAG,areaType.getValue()); 

now to get your value from a Json Object :

int areaValue = jsonObject.optInt(TAG,-1); AreaType areaType = AreaType.NONE.getType(areaValue); 

so if the areaValue is 1 for example, the AreaType will be "Area", and so on

回答5:

You should have custom serializer for Enum. Please check http://www.baeldung.com/jackson-serialize-enums.

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