Java JSONArray from Javascript JSONArray

Question

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.

James Sumners · Accepted Answer · 2012-01-13 14:24:23Z

1

    [
    [
        {
            "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"}]]

answered Jan 13, 2012 at 14:24

James Sumners

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4 Comments

ryandlf Over a year ago

When I create the JSONArray in java, it is creating the array of arrays. So I guess the original dataObj string is already an array, but how do I convert that for use in java so I can use a for loop on it etc?

James Sumners Over a year ago

Look at your JavaScript. You seem to have a bug where you add objects to the array. I cannot tell you anything else, because you didn't provide any JavaScript context.

ryandlf Over a year ago

In my javascript I am converting an array of object to what i'm thinking is a proper jsonArray using stringify. I verified that this is the problem, but I don't know how to avoid it. Before the I call the stringify on the array in javascript it is a perfectly working JS array. Should I be parsing it in prep for Java a different way?

ryandlf Over a year ago

Actually, this is an error in how i'm creating the javascript array. I verified that and the double occurs before I stringify. Your answer is correct for informing me of the initial problem, but i'll have the figure the rest out on my way as it goes a little to deep to get into with this question.

Boris Strandjev · Accepted Answer · 2012-01-13 14:35:10Z

0

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.

edited Jan 13, 2012 at 14:35

answered Jan 13, 2012 at 8:39

Boris Strandjev

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2 Comments

ryandlf Over a year ago

Get does not work either. I am assuming I am somehow building the array incorrectly. I am editing the question to include what the json array looks like when its passed in from javascript.

ryandlf Over a year ago

Please see comment above. The error is happening when I convert the javascript array using stringify in my javascript, but I don't know how else to convert it in prep for the java?

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