如果json可能具有不同的结构，如何将json转换为java对象

Question

I want to use java to make read return value from a url. The response json may be

{
   token:"blablablabla",
   expired: 7200
}

or of the form:

{
    errcode: 201
    errmsg: "out of limited"
}

I currently used jackson to convert json to java object. Yet in my condition, the response json may be different. All the example and tutorial I had found deal with a json string of only one form.

I would like to know what is the best practice when dealing with this situation.Currently I just catch (JsonMappingException e) and try again to convert to a different class.

Answer 1

The correct answer would be for the response to carry a clear marking that indicates what class it's intended to represent.

Without that, you're stuck with either trying things at random, or coming up with an alternative loading mechanism.

One approach might be to read the JSON into a tree or map or other tagged-data structure and then uses reflection to try to find a class whose fields match the field names given by the JSON... which would be a rather painful and fragile way to approach the problem.

Or you can skip the latter stage and just work with the abstract data structure, much as XML users work with the Document Object Model. Of course you wouldn't have access to any of the methods on specific objects this way, and you'd still have to come up with some sort of logic that recognized enough of the content to do something useful with it... but it would let you examine and manipulate those contents without having to know a priori which object was returned.

Answer 2

From what I understand, errcode and errmsg are common response attributes. So you may want to create an abstract class or interface like JsonResponse which holds these common attributes and have all the response classes () inherit JsonResponse . So in your code you can first check if the response has an error or not by checking these attributes.

Eg

public abstract Class JsonResponse {
  private String errcode;
  private String errmsg;
  //getters...
  //setters...
}

and,

public class MyResponse extends JsonResponse {
  private String token;
  private String expired;
  //getters...
  //setters...
}

EDIT: Changed to 'abstract class' as corrected by Allan.