Map within a list java to JSON conversion issue

Question

I am using gson.toJson to convert my java objects to JSON and I have an issue with a particular structure.

Here is what my code looks like:

  user_info.setUser_data(Arrays.asList(new HashMap<String, String>() {{
            put("x", "y");
            put("x1", "y2");
        }}, new HashMap<String, String>() {{
            put("x", "y");
            put("x1", "y2");
        }}));
  user_info.setUser_data2(new HashMap<String, Object>() {{
            put("x", 5);
        }});

Where user_data element is written as follows: (user_data2 is set in the following manner)

    private List<?> user_data= new ArrayList<>();

    public List<?> getUser_data() {
        return user_data;
    }

 public void setUser_data(List<?> user_data) {
        this.user_data = user_data;
    }

But after using gson.toJson I am getting the following empty result for user_data while user_data2 is not even bein converted.

  "user_data":[
         null,
         null
      ]
   }

What I expect to get is :

"user_data": [
        {
            "x": "y",
            "x1": "y2"
        },
        {
            "x": "y",
            "x1": "y2"
        }
    ],
    "user_data2": {
        "x": 5
    }
}

What am I getting wrong here?

1) Don't use double-brace initializers. It's just an anti-pattern with several drawbacks (creates extra classes that may hold references to outer classes): https://stackoverflow.com/questions/55118740/how-to-use-double-brace-initialization-for-map-of-map . 2) Gson does not _really_ support anonymous class serialization because of being unable to deserialize them properly (because of the outer class reference). Here is a very old issue for that: https://github.com/google/gson/issues/298 — terrorrussia-keeps-killing, Jan 20 '21 at 10:01
3) Note that Gson _may_ serialize such objects in some cases, but I suspect you have declared your `user_data` as `List — terrorrussia-keeps-killing, Jan 20 '21 at 10:04

Map within a list java to JSON conversion issue

0 Answers0