如何从Java中的Enum值返回具有所有属性的Enum对象

Question

I have got a scenario to return list of status as json which are available in Status Enum, My Enum Looks below

Example:-

public enum Status {

CREATED("100", "CREATED"), UPDATED("200", "UPDATED"), DELETED("300", "DELETED");

private final String id;
private final String name;

private Status(String id, String name) {
    this.id = id;
    this.name = name;
}

public String getId() {
    return id;
}

public String getName() {
    return name;
}

@Override
public String toString() {
    return name;
}

public List<Map<String, String>> lookup() {
    List<Map<String, String>> list = new ArrayList<>();
    for (Status s : values()) {
        Map<String, String> map = new HashMap<>();
        map.put("ID", s.getId());
        map.put("name", s.getName());
        list.add(map);
    }
    return list;

}
}

need the output like this:

[{id:"100",name:"CREATED"},{id:"200", name:"UPDATED"}...] I have written lookup method with List Of maps to build the response, Is there any better way or utility to convert the Enum to Object with all the properties available in Enum.

Is there any better way to do this?

Answer 1

You can use a library for JSON serialization like Gson or Jackson , and implement custom serialization in it.

Example Gson custom serializer :

class StatusSerializer implements JsonSerializer<Status> {
    public JsonElement serialize(Status status, Type typeOfSrc, JsonSerializationContext context) {
        JsonObject object = new JsonObject();
        object.addProperty("ID", status.getId());
        object.addProperty("name", status.getName());
        return object;
    }
}

You then use it as follows:

Gson gson = new GsonBuilder()
        .registerTypeAdapter(Status.class, new StatusSerializer())
        .create();
String json = gson.toJson(Status.CREATED);

which yields:

{"ID":"100","name":"CREATED"}

Answer 2

You can use Jackson to convert to JSON. Just include @JsonFormat(shape = Shape.OBJECT) at Enum declaration. This should give you the result.

Answer 3

Arrays.stream( Status.class.getEnumConstants() )
   .map( e -> Map.of( "id", e.getId(), "name", e.getName() )
   .collect( Collectors.toList() );

I'm on mobile and can't test but you get the general idea

Answer 4

You can use Stream API in Java 8. And use parallel to good perfomance.

List<Map<String, String>> list = Stream.of(Status.values()).parallel().map(temp -> {
        Map<String, String> obj = new HashMap<String, String>();
        obj.put("id", temp.getId());
        obj.put("name", temp.getName());
        return obj;
    }).collect(Collectors.toList());