使用GSON将String解析为JsonObject会产生IllegalStateException：这不是JSON对象

Question

I have the following code:

JsonParser parser = new JsonParser();
System.out.println("gson.toJson: "  + gson.toJson(roomList));
JsonObject json2 = parser.parse("{\"b\":\"c\"}").getAsJsonObject();
System.out.println("json2: " + json2);
JsonObject json = parser.parse(gson.toJson(roomList)).getAsJsonObject();
System.out.println("json: " + json);

It gives me the following output:

gson.toJson: [{"id":"8a3d16bb328c9ba201328c9ba5db0000","roomID":9411,"numberOfUsers":4,"roomType":"BigTwo"},{"id":"402881e4328b9f3a01328b9f3bb80000","roomID":1309,"numberOfUsers":4,"roomType":"BigTwo"},{"id":"402881e4328ba09101328ba09edd0000","roomID":1304,"numberOfUsers":4,"roomType":"BigTwo"},{"id":"402881e4328bb83601328bb8af640000","roomID":4383,"numberOfUsers":4,"roomType":"BigTwo"},{"id":"402881e4328bb83601328bd271fe0001","roomID":5000,"numberOfUsers":4,"roomType":"BigTwo"},{"id":"402881e4328bb83601328bd2e0e30002","roomID":2485,"numberOfUsers":4,"roomType":"BigTwo"},{"id":"402881e4328bb83601328bd3087b0003","roomID":6175,"numberOfUsers":4,"roomType":"BigTwo"},{"id":"402881e4328bb83601328bd35a840004","roomID":3750,"numberOfUsers":4,"roomType":"BigTwo"},{"id":"402881e4328bb83601328bd366250005","roomID":370,"numberOfUsers":4,"roomType":"BigTwo"},{"id":"402881e4328bb83601328bd3807d0006","roomID":9477,"numberOfUsers":4,"roomType":"BigTwo"}]
json2: {"b":"c"}
java.lang.IllegalStateException: This is not a JSON Object.

Can someone please help me parse my Json string to JsonObject? I have checked in http://jsonlint.com/ that my json is valid though.

Answer 1

It's because due to the JSON structure.. I have to put it into a JSONObject first, like so

JsonObject jsonObj = new JsonObject();
jsonObj.addProperty(ServerConstants.JSONoutput, gson.toJson(roomList));

Then I would deserialize like

 List<RoomData> roomList = gson.fromJson(jsonObj.get(CardGameConstants.JSONoutput).toString(), listType);
            for (RoomData roomData : roomList) {
                System.out.println(roomData.getRoomID());
            }

Answer 2

The problem with the code is that roomList is not a JsonObject as evident in the printed output. It's actually a JsonArray .

To fix the code, call .getAsJsonArray() (instead of .getAsJsonObject() )

JsonParser parser = new JsonParser();
System.out.println("gson.toJson: "  + gson.toJson(roomList));
JsonObject json2 = parser.parse("{\"b\":\"c\"}").getAsJsonObject();
System.out.println("json2: " + json2);
JsonArray json = parser.parse(gson.toJson(roomList)).getAsJsonArray();
System.out.println("json: " + json);

Answer 3

This should give you some basic idea.

ArrayList<String> roomTypes = new ArrayList<String>();

JSONArray jsonArray = new JSONArray(jsonString);

for(int i =0; i<jsonArray.length(); i++){
    roomTypes.add(jsonArray.getJSONObject(i).getString("roomType"));
}