send intent from service to activity

For this, you can use a BroadcastReceiver in your Activity.

Here is a great example I use to communicate continuously between Service <> Activity using BroadcastReceivers.

Here is another great example of communication between Service <> Activity. It uses Messenger and IncomingHandler.

BroadcastReceiver

I will make a quick example for your case.

This is your BroadcastReceiver for your Activity. It is going to receive your String:

//Your activity will respond to this action String
public static final String RECEIVE_JSON = "com.your.package.RECEIVE_JSON";

private BroadcastReceiver bReceiver = new BroadcastReceiver() {
    @Override
    public void onReceive(Context context, Intent intent) {
        if(intent.getAction().equals(RECEIVE_JSON)) {
            String serviceJsonString = intent.getStringExtra("json");
            //Do something with the string
        }
    }
};
LocalBroadcastManager bManager;

In your onCreate() of the activity

bManager = LocalBroadcastManager.getInstance(this);
IntentFilter intentFilter = new IntentFilter();
intentFilter.addAction(RECEIVE_JSON);
bManager.registerReceiver(bReceiver, intentFilter);

In your onDestroy() of the activity, make sure you unregister the broadcastReceiver.

bManager.unregisterReceiver(bReceiver);

And finally, in your Service onStart(), do this:

System.out.println("intent Received");
String jsonString = rottenTomatoesSearch(intent.getStringExtra("query"));
Intent RTReturn = new Intent(YourActivity.RECEIVE_JSON);
RTReturn.putExtra("json", jsonString);
LocalBroadcastManager.getInstance(this).sendBroadcast(RTReturn);

and your Activity will receive the intent with that json in it as an extra