Android JSON Parser

JSON stands for JavaScript Object Notation.It is an independent data exchange format and is the best alternative for XML. This chapter explains how to parse the JSON file and extract necessary information from it.

Android provides four differnet classes to manipulate JSON data. These classes areJSONArray,JSONObject,JSONStringer and JSONTokenizer.

The first step is to identify the fields in the JSON data in which you are interested in. For example. In the JSON given below we interested in getting temperature only.

{

"sys":
   {
      "country":"GB",
      "sunrise":1381107633,
      "sunset":1381149604
   },
"weather":[
   {
      "id":711,
      "main":"Smoke",
      "description":"smoke",
      "icon":"50n"
   }
],
"main":
   {
      "temp":304.15,
      "pressure":1009,
   }
}

JSON - Elements

An JSON file consist of many components. Here is the table defining the compoents of an JSON file and their description:

Sr.No	Component & description
1	Array([) In a JSON file , square bracket ([) represents a JSON array
2	Objects({) In a JSON file, curly bracket ({) represents a JSON object
3	Key A JSON object contains a key that is just a string. Pairs of key/value make up a JSON object
4	Value Each key has a value that could be string , integer or double e.t.c

JSON - Parsing

For parsing a JSON object, we will create an object of class JSONObject and specify a string containing JSON data to it. Its syntax is:

String in;
JSONObject reader = new JSONObject(in);

The last step is to parse the JSON. An JSON file consist of different object with different key/value pair e.t.c. So JSONObject has a separate function for parsing each of the component of JSON file. Its syntax is given below:

JSONObject sys  = reader.getJSONObject("sys");
country = sys.getString("country");
   
JSONObject main  = reader.getJSONObject("main");
temperature = main.getString("temp");

The method getJSONObject returns the JSON object. The method getString returns the string value of the specified key.

Apart from the these methods , there are other methods provided by this class for better parsing JSON files. These methods are listed below:

Sr.No	Method & description
1	get(String name) This method just Returns the value but in the form of Object type
2	getBoolean(String name) This method returns the boolean value specified by the key
3	getDouble(String name) This method returns the double value specified by the key
4	getInt(String name) This method returns the integer value specified by the key
5	getLong(String name) This method returns the long value specified by the key
6	length() This method returns the number of name/value mappings in this object..
7	names() This method returns an array containing the string names in this object.

Example

Here is an example demonstrating the use of JSONObject class. It creates a basic Weather application that allows you to parse JSON from google weather api and show the result.

To experiment with this example , you can run this on an actual device or in an emulator.

Steps	Description
1	You will use Eclipse IDE to create an Android application and name it as JSONParser under a package com.example.jsonparser. While creating this project, make sure you Target SDK and Compile With at the latest version of Android SDK to use higher levels of APIs.
2	Modify src/MainActivity.java file to add necessary code.
3	Modify the res/layout/activity_main to add respective XML components
4	Modify the res/values/string.xml to add necessary string components
5	Create a new java file under src/HandleJSON.java to fetch and parse XML data
6	Modify AndroidManifest.xml to add necessary internet permission
7	Run the application and choose a running android device and install the application on it and verify the results

Following is the content of the modifed main activity filesrc/com.example.jsonparser/MainActivity.java.

package com.example.jsonparser;

import android.os.Bundle;
import android.app.Activity;
import android.view.Menu;
import android.view.View;
import android.widget.EditText;

public class MainActivity extends Activity {

   private String url1 = "http://api.openweathermap.org/data/2.5/weather?q=";
   private EditText location,country,temperature,humidity,pressure;
   private HandleJSON obj;
   @Override
   protected void onCreate(Bundle savedInstanceState) {
      super.onCreate(savedInstanceState);
      setContentView(R.layout.activity_main);
      location = (EditText)findViewById(R.id.editText1);
      country = (EditText)findViewById(R.id.editText2);
      temperature = (EditText)findViewById(R.id.editText3);
      humidity = (EditText)findViewById(R.id.editText4);
      pressure = (EditText)findViewById(R.id.editText5);
   }

   @Override
   public boolean onCreateOptionsMenu(Menu menu) {
      // Inflate the menu; this adds items 
      //to the action bar if it is present.
      getMenuInflater().inflate(R.menu.main, menu);
      return true;
   }

   public void open(View view){
      String url = location.getText().toString();
      String finalUrl = url1 + url;
      country.setText(finalUrl);
      obj = new HandleJSON(finalUrl);
      obj.fetchJSON();

      while(obj.parsingComplete);
      country.setText(obj.getCountry());
      temperature.setText(obj.getTemperature());
      humidity.setText(obj.getHumidity());
      pressure.setText(obj.getPressure());

   }
}

Following is the content of src/com.example.jsonparser/HandleXML.java.

package com.example.jsonparser;

import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.io.StringWriter;
import java.io.UnsupportedEncodingException;
import java.net.HttpURLConnection;
import java.net.URL;
import java.util.ArrayList;
import java.util.List;
import java.util.Map;

import org.json.JSONObject;
import org.xmlpull.v1.XmlPullParser;
import org.xmlpull.v1.XmlPullParserFactory;

import android.annotation.SuppressLint;

public class HandleJSON {
   private String country = "county";
   private String temperature = "temperature";
   private String humidity = "humidity";
   private String pressure = "pressure";
   private String urlString = null;

   public volatile boolean parsingComplete = true;
   public HandleJSON(String url){
      this.urlString = url;
   }
   public String getCountry(){
      return country;
   }
   public String getTemperature(){
      return temperature;
   }
   public String getHumidity(){
      return humidity;
   }
   public String getPressure(){
      return pressure;
   }

   @SuppressLint("NewApi")
   public void readAndParseJSON(String in) {
      try {
         JSONObject reader = new JSONObject(in);

         JSONObject sys  = reader.getJSONObject("sys");
         country = sys.getString("country");

         JSONObject main  = reader.getJSONObject("main");
         temperature = main.getString("temp");

         pressure = main.getString("pressure");
         humidity = main.getString("humidity");

         parsingComplete = false;



        } catch (Exception e) {
           // TODO Auto-generated catch block
           e.printStackTrace();
        }

   }
   public void fetchJSON(){
      Thread thread = new Thread(new Runnable(){
         @Override
         public void run() {
         try {
            URL url = new URL(urlString);
            HttpURLConnection conn = (HttpURLConnection) url.openConnection();
            conn.setReadTimeout(10000 /* milliseconds */);
            conn.setConnectTimeout(15000 /* milliseconds */);
            conn.setRequestMethod("GET");
            conn.setDoInput(true);
            // Starts the query
            conn.connect();
         InputStream stream = conn.getInputStream();

      String data = convertStreamToString(stream);

      readAndParseJSON(data);
         stream.close();

         } catch (Exception e) {
            e.printStackTrace();
         }
         }
      });

       thread.start();   
   }
   static String convertStreamToString(java.io.InputStream is) {
      java.util.Scanner s = new java.util.Scanner(is).useDelimiter("\\A");
      return s.hasNext() ? s.next() : "";
   }
}

Following is the modified content of the xml res/layout/activity_main.xml.

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
   xmlns:tools="http://schemas.android.com/tools"
   android:layout_width="match_parent"
   android:layout_height="match_parent"
   android:paddingBottom="@dimen/activity_vertical_margin"
   android:paddingLeft="@dimen/activity_horizontal_margin"
   android:paddingRight="@dimen/activity_horizontal_margin"
   android:paddingTop="@dimen/activity_vertical_margin"
   tools:context=".MainActivity" >

   <TextView
      android:id="@+id/textView1"
      android:layout_width="wrap_content"
      android:layout_height="wrap_content"
      android:layout_alignParentLeft="true"
      android:layout_alignParentTop="true"
      android:layout_marginTop="15dp"
      android:text="@string/location"
      android:textAppearance="?android:attr/textAppearanceMedium" />

   <EditText
      android:id="@+id/editText1"
      android:layout_width="wrap_content"
      android:layout_height="wrap_content"
      android:layout_alignBottom="@+id/textView1"
      android:layout_alignParentRight="true"
      android:ems="10" />

   <TextView
      android:id="@+id/textView2"
      android:layout_width="wrap_content"
      android:layout_height="wrap_content"
      android:layout_alignLeft="@+id/textView1"
      android:layout_below="@+id/textView1"
      android:layout_marginTop="68dp"
      android:text="@string/country"
      android:textAppearance="?android:attr/textAppearanceSmall" />

   <TextView
      android:id="@+id/textView3"
      android:layout_width="wrap_content"
      android:layout_height="wrap_content"
      android:layout_below="@+id/textView2"
      android:layout_marginTop="19dp"
      android:text="@string/temperature"
      android:textAppearance="?android:attr/textAppearanceSmall" />

   <TextView
      android:id="@+id/textView4"
      android:layout_width="wrap_content"
      android:layout_height="wrap_content"
      android:layout_alignLeft="@+id/textView3"
      android:layout_below="@+id/textView3"
      android:layout_marginTop="32dp"
      android:text="@string/humidity"
      android:textAppearance="?android:attr/textAppearanceSmall" />

   <TextView
      android:id="@+id/textView5"
      android:layout_width="wrap_content"
      android:layout_height="wrap_content"
      android:layout_alignLeft="@+id/textView4"
      android:layout_below="@+id/textView4"
      android:layout_marginTop="21dp"
      android:text="@string/pressure"
      android:textAppearance="?android:attr/textAppearanceSmall" />

   <EditText
      android:id="@+id/editText2"
      android:layout_width="wrap_content"
      android:layout_height="wrap_content"
      android:layout_above="@+id/textView3"
      android:layout_toRightOf="@+id/textView3"
      android:ems="10" >

      <requestFocus />
   </EditText>

   <EditText
      android:id="@+id/editText3"
      android:layout_width="wrap_content"
      android:layout_height="wrap_content"
      android:layout_alignBaseline="@+id/textView3"
      android:layout_alignBottom="@+id/textView3"
      android:layout_alignLeft="@+id/editText2"
      android:ems="10" />

   <EditText
      android:id="@+id/editText4"
      android:layout_width="wrap_content"
      android:layout_height="wrap_content"
      android:layout_above="@+id/textView5"
      android:layout_alignLeft="@+id/editText1"
      android:ems="10" />

   <EditText
      android:id="@+id/editText5"
      android:layout_width="wrap_content"
      android:layout_height="wrap_content"
      android:layout_alignBaseline="@+id/textView5"
      android:layout_alignBottom="@+id/textView5"
      android:layout_alignRight="@+id/editText4"
      android:ems="10" />

   <Button
      android:id="@+id/button1"
      android:layout_width="wrap_content"
      android:layout_height="wrap_content"
      android:layout_alignLeft="@+id/editText2"
      android:layout_below="@+id/editText1"
      android:onClick="open"
      android:text="@string/weather" />

</RelativeLayout>

Following is the content of the res/values/string.xml.

<?xml version="1.0" encoding="utf-8"?>
<resources>
   <string name="app_name">JSONParser</string>
   <string name="action_settings">Settings</string>
   <string name="hello_world">Hello world!</string>
   <string name="location">Location</string>
   <string name="country">Country:</string>
   <string name="temperature">Temperature:</string>
   <string name="humidity">Humidity:</string>
   <string name="pressure">Pressure:</string>
   <string name="weather">Weather</string>
</resources>

Following is the content of AndroidManifest.xml file.

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
   package="com.example.jsonparser"
   android:versionCode="1"
   android:versionName="1.0" >

   <uses-sdk
      android:minSdkVersion="8"
      android:targetSdkVersion="17" />
   <uses-permission android:name="android.permission.INTERNET"/>

   <application
      android:allowBackup="true"
      android:icon="@drawable/ic_launcher"
      android:label="@string/app_name"
      android:theme="@style/AppTheme" >
   <activity
      android:name="com.example.jsonparser.MainActivity"
      android:label="@string/app_name" >
      <intent-filter>
         <action android:name="android.intent.action.MAIN" />

         <category android:name="android.intent.category.LAUNCHER" />
      </intent-filter>
   </activity>
</application>
</manifest>

Let's try to run our JSONParser application we just modified. I assume you had created your AVD while doing environment setup. To run the app from Eclipse, open one of your project's activity files and click Run . icon from the toolbar. Eclipse installs the app on your AVD and starts it and if everything is fine with your setup and application, it will display following Emulator window:

Now what you need to do is to enter any location in the location field. For example , i have entered newyork. Press the weather button , when you enter the location. The following screen would appear in you AVD:

Now when you press the weather button, the application will contact the Google Weather API and will request for your necessary JSON location file and will parse it. In case of newyork following file would be returned:

London Temperature from google weather api

Note that this temperature is in kelvin, so if you want to convert it into more understandble format , you have to convert it into Celcius.