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Java/Android JSONArray inside JSONObject returning null

I'm developing an app for android that communicates with a server and receives JSON responses from it. Recently I changed the responses structure to contain more information about the requests.
Initially my responses where just the response from a mysqli_query encoded to JSON by the php function json_encode, and looked like this:
[
{"id":"31","description":"Hello"},
{"id":"32","description":"World"},
]
And to retrieve the objects, I would just create a new JSONArray object by calling my_json_array=new JSONArray(response) and iterate over it.
But now, my new responses contain extra data, like this:
{
"error":false,
"idCode":0,
"message":[
{
"id":"32",
"description":"Hello"
},
{
"id":"31",
"description":"World"
}
]
}
So now, as far as I understand, I need to convert this response to a JSONObject, and then extract the message as a JSONarray object by calling my_json_object.getJSONArray("message");.
I can extract the data from the "error" and the "idCode" fields normally, but when I try to extract the JSONArray from "message" it returns null, and no exceptions are thrown except for the NullPointerException.
I've validated the JSON string here, escaped the characters that could be problematic for java like the double quotes, removed uppercases, written the response as a single line, removed the double quotes surrounding the "id" value, used single quotes instead of double quotes, used harcoded string instead of the response from the server, checked the unicode representation of the string to see if contains any invalid characters (and it looks like it doesn't) and I don't know what else to do. Something to notice: the method toString() on the object returns the string "null", and based on the toString() method of the JSONObjects, it seems like the problem comes from the JSONStringer library, and going deeper on the classes it looks like the exception that there is a nesting problem, but I can't find any problem in my JSON string.
The important part of the code:
public String getResponse(){
web_helper.sendRequest();
//everything fine over here
return web_helper.getResponse();
}
public void printData(){ throws JSONExpection
JSONObject my_json_object=new JSONObject(getResponse());
System.out.println("error: "+my_json_object.getBoolean("error"));
System.out.println("idCode: "+my_json_object.getInt("idCode"));
JSONArray my_json_array=my_json_object.getJSONArray("message");
//not sure if the next part works because my_json_array is null
for(int i=0; i<my_json_array.length(); i++){
JSONObject obj=my_json_array.getJSONObject(i);
System.out.println("id: "+obj.getInt("id"));
System.out.println("description: "+obj.getString("description"));
}
}
Any help is appreciated, thank you in advance!.

Processing: how to check if JSON Objects are bound

Since the Processing forum is down I hope one of you guys can help me out.
I made a Processing sketch that pulls data from an API (test here: http://www.europeana.eu/portal/api/console.html ) in JSON-format and reads some fields of this data for visualization. Everything works fine so far except when there are fields that are not bound to every JSONObject.
This is the code for the retrieval of the data:
JSONObject json;
json = loadJSONObject("data.json"); // loading my JSON file into the object
JSONArray CHOData = json.getJSONArray("items"); // array of the items I want data from
for (int i = 0; i < CHOData.size(); i++) {
JSONObject CHO = CHOData.getJSONObject(i); // get a specific item
JSONArray previewObj = CHO.getJSONArray("edmPreview"); // this field is an array, so I need to store it in a JSONArray object first
String[] previewArray = previewObj.getStringArray(); // here I store it in my actual string array
String preview = previewArray[0]; // I only need the first element
}
As you can see, I want the first string of the "edmPreview" array in the object. When I run the sketch, I get an error: "JSONObject["edmPreview"] not found."
This is of course because not every item has such an object. But how can I test if there is an object with this name in an item? I tried with if(CHO.getJSONObject("edmPreview") != null), but same error. Is there a way to look into the JSONObject and check the data values for something called "edmPreview"? There is no such function explained in the Processing reference.
The JSON file essentially looks as follows:
{
"items": [
{
"id": "someID",
"edmPreview": [
"http://europeanastatic.eu/api/image?uri=someimage.jpg"
],
// some other fields
}, // some other items
]
}
I'm new to this JSON-stuff, so maybe I miss something important... Thanks for the help!

So I found the answer myself, but not in the Processing reference, but in the actual reference for the JSONObject class in Java (http://www.json.org/javadoc/org/json/JSONObject.html). I tried some of the methods there and found that hasKey() (which is actually something I came up with myself, combining the method "has()" with the term "key", pure coincidence) as a boolean value works very well:
String preview = "";
if (CHO.hasKey("edmPreview")) {
JSONArray previewObj = CHO.getJSONArray("edmPreview");
String[] previewArray = previewObj.getStringArray();
preview = previewArray[0];
}
So now I learned that Processing is essentially just Java and sometimes not every method is written in the Reference. :-)

Parsing a json file in JAVA

I have json file. Now, a field names "refs" isn't available in every array. So, what is procedure to parse this kind of field. Because, when I try to parse the json file, 1st array don't have "refs" field but 2nd array hasn't. That's why it throw Null Pointer exception. I tried with this code
JSONArray jsonArray = new JSONArray(tokener);
for (int index = 0; index < jsonArray.length(); index++) {
JSONObject jsonObject = jsonArray.getJSONObject(index);
if(!jsonObject.getString("refs").equalsIgnoreCase(null)){
String refs = jsonObject.getString("refs");
}
}
But, it's not working. What is the way to handle this situation or what is the way to solve that problem. Thank you.

If you are not sure that the key is present, call has to check first.

the problem is in your if statement....
if(!jsonObject.getString("refs").equalsIgnoreCase(null)){
What you should be writing is:
if(!jsonObject.has("refs")){
Hope that helps

Try this
if(jsonObject.has("refs")){
refs = jsonObject.getString("refs");
}

You can do it by just replacing 'if' condition like this, It works for me hope useful to u also.
if(jObj.optString("refs") != null)

How to obtain the content from Multi-Level JSON format in JAVA?

For example, a kind of JSON as below:
{ "x":"1","y":"2","z":{"a":"1","b":"2","c":"3"}}
Put this as string in JSONObject argument:
JSONObject jaob=new JSONObject(xxx)
and from method "get("x")" of JSONObject I can obtain the value "1"
jaob.get("x")
But how to get "a" of the second level JSON format "z"???
When I try to obtain by
JSONObject(jaob.get("z").toString()).get("a")
but it doesn't work.
Does any one have the idea?
Any response is appreciated, thanks

jaob.getJSONObject("Z").getString("a")
alternatively, you could use getLong or getString on a.
If you read the javadocs it's pretty easy stuff. The reason yours didn't work is that get returns a java.lang.Object not a JSONObject or JSONArray.

Have you tried
JSONObject jaob = new JSONObject(xxx);
jaob.getJSONArray("z");
//or
jaob.getJSONObject("z");
they both return JSONObject according to JSONObject

Java JSONArray from Javascript JSONArray

I am passing a json object from javascript to a java servlet using ajax.
var jsonObj = JSON.stringify(objArray); //Then I pass it to Java using ajax.
In my Java I am getting the json string from the request, then creating a jsonarray, then looping through that array and i'm getting errors when trying to pull one of the json objects from the array.
String dataObj = request.getParameter("obj");
String sql = request.getParameter("sql");
ArrayList<Object> returnArray = new ArrayList<Object>();
int key;
//Get type of object being passed.
JSONArray jsonArray = JSONArray.fromObject(dataObj);
for(int i=0; i<jsonArray.size(); i++) {
String obj = new Gson().toJson(jsonArray.getJSONObject(i)); //This is where i'm getting an error
String className = getClassName(jsonArray.getJSONObject(i));
Class targetClass = null;
try {
targetClass = Class.forName(className);
} catch (ClassNotFoundException e) {
e.printStackTrace();
}
//Create Object
Object data = new Gson().fromJson(obj, targetClass);
I'm posting the relevant code, the for loop isn't closed because the rest of the code is quite long, and this is the part where i'm getting the error.
net.sf.json.JSONException: JSONArray[0] is not a JSONObject.
Here is what the json array looks like when its passed in from javascript. This is a println of the jsonArray object.
[{"number":"(123) 456-7050","type":"Home","contactId":1,"id":16662,"className":"beans.PhoneNumber","position":0}]
With one object in it, this code works. But as soon as I get 2 or more, my error comes up.
[[{"number":"(123) 456-7050","type":"Home","contactId":1,"id":16662,"className":"beans.PhoneNumber","position":1},{"number":"(555) 555-1233","type":"Mobile","contactId":1,"id":16656,"className":"beans.PhoneNumber","position":0},{"number":"(999) 999-9999","type":"Home","contactId":1,"id":16664,"className":"beans.PhoneNumber","position":3},{"number":"(222) 222-2222","type":"Home","contactId":1,"id":16666,"className":"beans.PhoneNumber","position":4}]]
It almost looks like when i'm passing more than one object, it create an array of an array, which could be why its not working. But how do I avoid doing that when i'm passing a jsonarray from javascript? Using just the dataObj I have no access to size or get to loop through it.

[
[
{
"number":"(123) 456-7050","type":"Home",
"contactId":1,
"id":16662,
"className":"beans.PhoneNumber",
"position":1
},
{
"number":"(555) 555-1233",
"type":"Mobile",
"contactId":1,
"id":16656,
"className":"beans.PhoneNumber",
"position":0
},
{
"number":"(999) 999-9999",
"type":"Home",
"contactId":1,
"id":16664,
"className":"beans.PhoneNumber",
"position":3
},
{
"number":"(222) 222-2222",
"type":"Home",
"contactId":1,
"id":16666,
"className":"beans.PhoneNumber",
"position":4
}
]
]
This is not an array of objects. This is an array of arrays of objects. According to your description, you are expecting something like the following to be fed to your Java:
[{"foo":"bar"}, {"bar":"baz"}]
But you are really trying to parse:
[[{"foo":"bar"}, {"bar":"baz"}]]

I am not completely sure, because you have not shared the json that you are trying to parse, but the most probable error you have is just what it says: the first element of the array is not JSONObject. Note that string values, lons and booleans are not JSONObjects. I would suggest you to use the more genereal JSONArray.get and check instance of what class it is. Maybe this can head you to the problem with the json you have. If I got it completely wrong - write back and I will try to help. In such a case it will be still useful to share the results of the proposed experiment.
EDIT:
This is double array -> maybe you using getJSONArray(int index) will help you. as the other answer mentioned - this is array of arrays. Also consider changing the javascript to reduce the level of arrays included.