JSON Parsing in Android

1. Android and JSON

1.1. Android and JSON

JSON is a very condense data exchange format. Android includes the json.org libraries which allow to work easily with JSON files.

1.2. Twitter

Twitter is a great source for JSON. You can just call a URI and retrieve JSON. Here are some examples:

Table 1. Twitter URI's

URI	Description
http://twitter.com/statuses/user_timeline/vogella.json	Get the timeline of user vogella .
http://search.twitter.com/search.json?q=android	Search for the term "android" on Twitter.
http://twitter.com/statuses/user_timeline/vogella.json	Returns the user data of user vogella .

Please note that some URI's return a JSONObject object while others return a JSONArray. The following coding uses an URI which returns an JSONArray.

2. Reading JSON

Create a new Android project "de.vogella.android.twitter.json" with the package "de.vogella.android.twitter.json" and the activity "ParseJSON".
Create the following coding for the activity. This will download the twitter feed for the user http://twitter.com/ and write the number of entries and the text messages to the Android log file.

package de.vogella.android.twitter.json;

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;

import org.apache.http.HttpEntity;
import org.apache.http.HttpResponse;
import org.apache.http.StatusLine;
import org.apache.http.client.ClientProtocolException;
import org.apache.http.client.HttpClient;
import org.apache.http.client.methods.HttpGet;
import org.apache.http.impl.client.DefaultHttpClient;
import org.json.JSONArray;
import org.json.JSONObject;

import android.app.Activity;
import android.os.Bundle;
import android.util.Log;

public class ParseJSON extends Activity {
	/** Called when the activity is first created. */
	@Override
	public void onCreate(Bundle savedInstanceState) {
		super.onCreate(savedInstanceState);
		setContentView(R.layout.main);
		String readTwitterFeed = readTwitterFeed();
	try {
		JSONArray jsonArray = new JSONArray(readTwitterFeed);
		Log.i(ParseJSON.class.getName(),
			"Number of entries " + jsonArray.length());
		for (int i = 0; i < jsonArray.length(); i++) {
		JSONObject jsonObject = jsonArray.getJSONObject(i);
		Log.i(ParseJSON.class.getName(), jsonObject.getString("text"));
		}
	} catch (Exception e) {
		e.printStackTrace();
	}
}

	public String readTwitterFeed() {
	StringBuilder builder = new StringBuilder();
	HttpClient client = new DefaultHttpClient();
	HttpGet httpGet = new HttpGet(
		"http://twitter.com/statuses/user_timeline/vogella.json");
	try {
		HttpResponse response = client.execute(httpGet);
		StatusLine statusLine = response.getStatusLine();
		int statusCode = statusLine.getStatusCode();
		if (statusCode == 200) {
			HttpEntity entity = response.getEntity();
			InputStream content = entity.getContent();
			BufferedReader reader = new BufferedReader(
					new InputStreamReader(content));
			String line;
			while ((line = reader.readLine()) != null) {
				builder.append(line);
			}
		} else {
		Log.e(ParseJSON.class.toString(), "Failed to download file");
	}
	} catch (ClientProtocolException e) {
		e.printStackTrace();
	} catch (IOException e) {
		e.printStackTrace();
	}
	return builder.toString();
}
} 

To run this example assign the uses-permission to your "AndroidManifest.xml" for "android.permission.INTERNET".

3. Write JSON

Writing JSON is very simple. Just create the JSONObject or JSONArray and use the toString() method.

public void writeJSON() {
	JSONObject object = new JSONObject();
	try {
		object.put("name", "Jack Hack");
		object.put("score", new Integer(200));
		object.put("current", new Double(152.32));
		object.put("nickname", "Hacker");
	} catch (JSONException e) {
		e.printStackTrace();
	}
	System.out.println(object);
}