Android - XML Parsers

XML stands for Extensible Mark-up Language.XML is a very popular format and commonly used for sharing data on the internet. This chapter explains how to parse the XML file and extract necessary information from it.

Android provides three types of XML parsers which are DOM,SAX and XMLPullParser. Among all of them android recommend XMLPullParser because it is efficient and easy to use. So we are going to use XMLPullParser for parsing XML.

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

< current>
   
   < city id="2643743" name="London">
      < coord lon="-0.12574" lat="51.50853"/>
      < country>GB
      < sun rise="2013-10-08T06:13:56" set="2013-10-08T17:21:45"/>
   < /city>
   
   < temperature value="289.54" min="289.15" max="290.15" unit="kelvin"/>
   < humidity value="77" unit="%"/>
   < pressure value="1025" unit="hPa"/>
< /current>

XML - Elements

An xml file consist of many components. Here is the table defining the components of an XML file and their description.

XML - Parsing

In the next step, we will create XMLPullParser object , but in order to create that we will first create XmlPullParserFactory object and then call its newPullParser() method to create XMLPullParser. Its syntax is given below −

private XmlPullParserFactory xmlFactoryObject = XmlPullParserFactory.newInstance();
private XmlPullParser myparser = xmlFactoryObject.newPullParser();

The next step involves specifying the file for XmlPullParser that contains XML. It could be a file or could be a Stream. In our case it is a stream.Its syntax is given below −/p>

myparser.setInput(stream, null);

The last step is to parse the XML. An XML file consist of events, Name, Text, AttributesValue e.t.c. So XMLPullParser has a separate function for parsing each of the component of XML file. Its syntax is given below −

int event = myParser.getEventType();
while (event != XmlPullParser.END_DOCUMENT)  {
   String name=myParser.getName();
   switch (event){
      case XmlPullParser.START_TAG:
      break;
      
      case XmlPullParser.END_TAG:
      if(name.equals("temperature")){
         temperature = myParser.getAttributeValue(null,"value");
      }
      break;
   }		 
   event = myParser.next(); 					
}

The method getEventType returns the type of event that happens. e.g: Document start , tag start e.t.c. The method getName returns the name of the tag and since we are only interested in temperature , so we just check in conditional statement that if we got a temperature tag , we call the method getAttributeValue to return us the value of temperature tag.

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

Example

Here is an example demonstrating the use of XML DOM Parser. It creates a basic application that allows you to parse XML.

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

Following is the content of the modified main activity file MainActivity.java.

package com.example.sairamkrishna.myapplication;

import java.io.InputStream;
import javax.xml.parsers.DocumentBuilder;
import javax.xml.parsers.DocumentBuilderFactory;
import org.w3c.dom.Document;
import org.w3c.dom.Element;
import org.w3c.dom.Node;
import org.w3c.dom.NodeList;
import android.app.Activity;
import android.os.Bundle;
import android.widget.TextView;

public class MainActivity extends Activity {
   TextView tv1;

   @Override
   public void onCreate(Bundle savedInstanceState) {
      super.onCreate(savedInstanceState);
      setContentView(R.layout.activity_main);
      tv1=(TextView)findViewById(R.id.textView1);
		
      try {
         InputStream is = getAssets().open("file.xml");

         DocumentBuilderFactory dbFactory = DocumentBuilderFactory.newInstance();
         DocumentBuilder dBuilder = dbFactory.newDocumentBuilder();
         Document doc = dBuilder.parse(is);

         Element element=doc.getDocumentElement();
         element.normalize();

         NodeList nList = doc.getElementsByTagName("employee");
			
         for (int i=0; i< nList.getLength(); i++) {

            Node node = nList.item(i);
            if (node.getNodeType() == Node.ELEMENT_NODE) {
               Element element2 = (Element) node;
               tv1.setText(tv1.getText()+"\nName : " + getValue("name", element2)+"\n");
               tv1.setText(tv1.getText()+"Surname : " + getValue("surname", element2)+"\n");
               tv1.setText(tv1.getText()+"-----------------------");
            }
         }
			
      } catch (Exception e) {e.printStackTrace();}

   }
	
   private static String getValue(String tag, Element element) {
      NodeList nodeList = element.getElementsByTagName(tag).item(0).getChildNodes();
      Node node = nodeList.item(0);
      return node.getNodeValue();
   }

}

Following is the content of Assets/file.xml

< ?xml version="1.0"?>
< records>
   < employee>
      < name>Sairamkrishna< /name>
      < surname>Mammahe< /surname>
      < salary>50000< /salary>
   < /employee>
	
   < employee>
      < name>Gopal < /name>
      < surname>Varma< /surname>
      < salary>60000< /salary>
   < /employee>
	
   < employee>
      < name>Raja< /name>
      < surname>Hr< /surname>
      < salary>70000< /salary>
   < /employee>
	
< /records>

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

< ?xml version="1.0" encoding="utf-8"?>
< 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" />
< /RelativeLayout>

Following is the content of AndroidManifest.xmlfile.

< ?xml version="1.0" encoding="utf-8"?>
< manifest xmlns:android="http://schemas.android.com/apk/res/android"
   package="com.example.sairamkrishna.myapplication" >
   < application
      android:allowBackup="true"
      android:icon="@mipmap/ic_launcher"
      android:label="@string/app_name"
      android:theme="@style/AppTheme" >
      
      < activity
         android:name=".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 application we just modified. I assume you had created your AVD while doing environment setup. To run the app from Android studio, open one of your project's activity files and click Run icon from the toolbar. Android studio 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 −