ToJson() 공개 메소드

public ToJson ( ) : string
리턴 string
 public MessageResult sendPush(PushPayload payload) 
 {
     Preconditions.checkArgument(payload != null, "pushPayload should not be empty");
     payload.Check();
     String payloadJson = payload.ToJson();
     return sendPush(payloadJson);
 }