cannot cast JSONObject to JSONArray

Question

I'm trying to convert the JSON data that i get back to an array so I can use the data in a listView.

I got the following code:

JSONObject jsonobject;
jsonobject = JSONFunctions.getJSONfromURL("example/url");

ArrayList<String> list = new ArrayList<String>();
JSONArray jsonArray = (JSONArray)jsonobject;
if (jsonArray != null) {
   //do something with it
}

Note: I don't have any experience with Java.
The method getJSONfromURL returns the JSON of the given URL that works just fine but the error is in JSONArray jsonArray = (JSONArray)jsonobject;

It gives the following error: cannot cast JSONObject to JSONArray I've also tried this: JSONArray jsonArray = (JSONObject)(JSONArray)jsonobject;

I can't figure out what i'm doing wrong.

So how can I cast my jsonobject to a normal array that I can use as data for my listView?

I'd take a look at the JSON you're getting back from the URL (and post it here if you can). Are you sure it's an array? Generally speaking, returning a top-level array is considered a security vulnerability. — Ian McLaird
– Ian McLaird, Commented Feb 25, 2015 at 14:08
This? json.org/javadoc/index.html There is no class named JSONFunctions. — xehpuk
– xehpuk, Commented Feb 25, 2015 at 14:08
Yes that's what i'm using. Im sorry for the misunderstanding JSONFunctions is a class that I wrote myself. — Bas
– Bas, Commented Feb 25, 2015 at 14:09
If you expect an array, you can use new JSONArray(String). — xehpuk
– xehpuk, Commented Feb 25, 2015 at 14:12

xehpuk · Accepted Answer · 2015-02-25 15:01:01Z

1

A JSONObject is distinct from a JSONArray. If you try new JSONObject("['test', 'array']"), you will get a JSONException: A JSONObject text must begin with '{' at 1 [character 2 line 1].

Try whether this works for you:

static JSONArray fromUrl(URL url) throws IOException {
    try (
        InputStream openStream = url.openStream();
        BufferedInputStream bis = new BufferedInputStream(openStream);
        Scanner scanner = new Scanner(bis, StandardCharsets.UTF_8.name());
    ) {
        if (!scanner.useDelimiter("\\A").hasNext()) {
            throw new EOFException("empty response");
        }
        return new JSONArray(scanner.next());
    }
}

answered Feb 25, 2015 at 15:01

xehpuk

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2 Comments

Bas Over a year ago

Thanks for your answer but your code throws an error at the last line return new JSONArray. Error: Unhandled exception:JSONException

xehpuk Over a year ago

@Bas In the sources I downloaded (github.com/douglascrockford/JSON-java/blob/master/…) it doesn't need to be handled because it extends RuntimeException. Then you have to handle the exception by adding a catch-clause or declare it to be thrown by putting it in the throws-clause (throws IOException, JSONException). But this is basic Java knowledge you should definitely acquire.

Schleis · Accepted Answer · 2015-02-25 14:58:53Z

0

JSONObject is like a Map in java. Key-value pair. So, you should iterate like iterating a Map:

Iterator iterator = jsonobject.keys();
JSONArray jsonArray = new JSONArray();

while (iterator.hasNext()){
    String key = (String) iterator.next(); // assuming the key to be a String
    // You can put the key also if you want. But, It does not make any sense to do so.
    jsonArray.put(jsonobject.get(key)); 
}

edited Feb 25, 2015 at 14:58

Schleis

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answered Feb 25, 2015 at 14:04

Paul-E

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