JSON 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. JSON Example: Twitter

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

Table 1. Twitter URIs

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/users/show/vogella.json	Returns the user data of user vogella.

Please note that some URIs return a JSONObject object while others return a 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/vogella 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);
}