Check if JSONObject key exists

问题

I'm making api calls to a back-end who always has a JSONArray series and sometimes has a JSONArray places. In the code below, I am trying to write an if statement that says, whenever there is no places array, make another http request. However, I am not getting a nullpointer, it just throws a JSON Exception saying there is no value for places. What can I put as the terminating condition, for when places has no value? I have tried places == null and that hasn't worked.

try{
    JSONArray places = passingObject.getJSONArray("places");
    JSONArray series = passingObject.getJSONArray("series");

    if(some condition){
       //do something else
    }
}catch(JSONException e){
    Log.d("JSON EXCEPTION" e.getMessage());
}

回答1:

Or you can use http://www.json.org/javadoc/org/json/JSONObject.html#optJSONArray(java.lang.String)

JSONArray places = passingObject.optJSONArray("places");
if(places == null){...}

optJSONArray(); It returns null if there is no such key, or if its value is not a JSONArray.

回答2:

Check if the object has a key called places.

if (passingObject.has("places") {
    JSONArray places = passingObject.getJSONArray("places");
} else {
    askServerAgain();
}

来源：https://stackoverflow.com/questions/32470315/check-if-jsonobject-key-exists