错误：JSONObject [“结果”]不是JSONObject

Question

I am fetching a JSONObject "result" from the following JSONObject:

{
    "success" : true,
    "message" : "",
    "result" : {
            "uuid" : "e606d53c-8d70-11e3-94b5-425861b86ab6"
        }
}

I am using this code:

    CloseableHttpClient httpclient = HttpClients.createDefault();
    String url = "some url";
    HttpGet httpget20 = new HttpGet(url);
    httpget20.setHeader("apisign",buildHmacSignature(url, apisecret));
      try (   CloseableHttpResponse response2 = httpclient.execute(httpget20)){
        HttpEntity entity = response2.getEntity();
        JSONObject obj2 = new JSONObject(EntityUtils.toString(entity));
        JSONObject result = obj2.getJSONObject("result");

obj2 is the whole json object including "success", "message" and "result". However, this line of code generates the following error message:

Exception in thread "AWT-EventQueue-0" org.json.JSONException: JSONObject["result"] is not a JSONObject.

I am not sure how a JSONObject can not be a JSONObject. Can someone explain the problem here?

Answer 1

JSONObject.getJSONObject can return a JSONObject only. It will not return boolean , long or String , and it will not return JSONObject.NULL in particular, because that is not a JSONObject itself (it says Java Object in the docs, and has a specific private type in the implementation).
Use isNull for checking it beforehand or just accept that it throws an exception and prepare for it. Of course you can also use the generic get and check the result against JSONObject.NULL afterwards, perhaps use instanceof , just none of these will make the code simpler and all of them will introduce casting/casting attempts at some point.

I was linking the Android docs for readability, but you can of course dig into source code too, like getJSONObject . You can find the NULL at the beginning of the same file if you are interested.