如何从JSON字符串获取数据？

Question

Here is my code:

try {
    JSONObject json = (JSONObject) new JSONTokener(result).nextValue();
    System.out.println(json);
    JSONObject json2 = json.getJSONObject("data");
    String test = json2.getString("headline");
    System.out.println(test);
} catch (JSONException e) {
    e.printStackTrace();
}

My String values start with the object data . So I am trying to get that object first and then capture the the object headline inside that.

My problem is, it is not taking the object data from the string. Once I reach the line JSONObject json2 = json.getJSONObject("data"); , it throws the exception. Please shed some light on this.

"data": [
    {
        "headline": "Close Update"
        "docSource": "MIDNIGHTTRADER",
        "source": "MTClosing",
        "dateTime": "2015-10-23T16:42:46-05:00",
        "link": "Markets/News",
        "docKey": "1413-A1067083-1B14K77PVTUM1O7PCAFMI3SJO4",
    },

Answer 1

The value for the key data is a JSON array containing one object, and not an object itself.

To get that object inside data , replace your line that throws an exception with the following:

JSONObject json2 = json.getJSONArray("data").get(0);

This gets the data array as a JSONArray object and then gets the 0th element, which is the object you want.

Answer 2

Your data "object", isn't actually an object, it's an array, notice the opening square bracket... I'm assuming in your actual code, it closes with one too.

"data": [{
  "headline": "Close Update"
  "docSource": "MIDNIGHTTRADER",
  "source": "MTClosing",
  "dateTime": "2015-10-23T16:42:46-05:00",
  "link": "Markets/News",
  "docKey": "1413-A1067083-1B14K77PVTUM1O7PCAFMI3SJO4",
}]

Try json.getJSONArray("data")[0] instead... or whatever index you need

try {
        JSONObject json = (JSONObject) new JSONTokener(result).nextValue();
        System.out.println(json);
        JSONObject json2 = json.getJSONArray("data")[0];
        String test = json2.getString("headline");
        System.out.println(test);
    }
catch (JSONException e) {
        e.printStackTrace();

Answer 3

Your problem is based on the fact that your service returns and array instead of a single json object, so from here you can follow this suggestions to process directly from the JSONArray Can't access getJSONArray in java , or, at server side you can encapsulate your response array into another object like this (java example):

public class Data<T> {

    private List<T> elements;

    public ObjectSugetionsDTO(){

And build the response like this:

return new ResponseEntity<Data<YourInternalRepresentation>>(
                    new Data<YourInternalRepresentation>(yourMethodCallForTheArray()),
                    HttpStatus.OK);

I have found the second way to be better at keeping my API cleaner and more readable

EDIT: Better way

I whould also suggest the use of retrofit ( http://square.github.io/retrofit/ ), by doing so, your service calls is resumed to (Example of calling and API that retrieves a list of users):

public class UserService {

    public static IUserService getUserService() {
        return RestAdapterManager.createService(IUserService.class );
    }

    public interface IUserService{
        @GET("/api/users")
        public void getAllUsers(Callback<List<User>> callback);

    }
}

and the service call itself

UserService.getUserService().getAllUsers(new Callback<List<User>>() {
                    @Override
                    public void success(List<User> users, Response response) {
                        Log.d("Exito! " , "" + users.size());
                    }

                    @Override
                    public void failure(RetrofitError error) {
                        Log.d("Fail!", error.getUrl());
                    }
                });

The simple inicialization of the connection object

public static <S> S createService(Class<S> serviceClass, String username, String password) {
    RestAdapter.Builder builder = new RestAdapter.Builder()
        .setEndpoint(API_BASE_URL);//Your api base url

    RestAdapter adapter = builder.setLogLevel(RestAdapter.LogLevel.FULL).build(); //change the logging level if you need to, full is TOO verbose
    return adapter.create(serviceClass);
}