XML Parsing in Android using DOM Parser

Android DOM(Document Object Model) parser is a program that parses an XML document and extracts the required information from it. This parser uses an object-based approach for creating and parsing the XML files. In General, a DOM parser loads the XML file into the Android memory to parse the XML document. This results in more consumption of memory. The document is parsed through every possible node in the XML file. The XML file that contains the information to be extracted includes the following four main components:

1. Prolog: The XML file will start with a prolog. Prolog contains the information about a file, which is available in the first line.
2. Events: Events such as document start and end, tag start and end, etc. are contained in the XML file
3. Text: It is a simple text present in between the opening and closing XML tag elements.
4. Attributes: They are the additional properties of a tag present within the label.

Note that we are going to implement this project using the Kotlin language.  One may also perform XML Parsing in another two ways. Please refer to the below articles:

• XML Parsing in Android using SAX Parser
• XML Parsing in Android using XmlPullParser

What we are going to do?

1. We need to have an XML file with some information so that we would make one. Place this file under the assets folder. This file is called and would be parsed.
2. We want to show this data in the form of a list to implement a list view.
3. In the Main program, we called the information file (under the assets folder) from the assets folder, and this is provided as an input stream.
4. Using a DocumentBuilderFactory, we would create a new instance.
5. Using a DocumentBuilder, we generate a new document builder.
6. Using a Document method, we parse the input stream.
7. As the information is in the form of nodes, we would create a NodeList and iterate through every node using a FOR loop.
8. Specific information would be extracted in this loop and added to a list (declared earlier in the code).
9. Using a ListAdapter, the data is broadcasted into the list view layout file.

Approach

To parse an XML file using a DOM parser in Android, we follow the following steps:

Step 1: Create a New Project

To create a new project in Android Studio please refer to How to Create/Start a New Project in Android Studio. Note that select Kotlin as the programming language.

Step 2: Create an assets folder

Create an assets folder under the main folder in the Project Layout. Create an Android Resource File in this folder, where we shall put the information in the form of XML. Name this file as information.xml. For doing so refer to the following steps:

Click on Project as shown on the left side of the below image. 

Expand until you find the main folder, right-click on it, go to New > Folder > Assets Folder

Then just click on the Finish button.

Now the asset folder is created successfully. Right-Click on the Assets Folder > New > Android Resource FIle 

Give it name Information, change type to XML, and finish.

Note: Sometimes, right-clicking on the Assets folder and creating an Android Resource File creates a file in the res folder. If this happens, cut our file and paste it directly into the assets folder. This happens due to some internal settings.

Paste this information which is in the form of XML, that is to be displayed in the information.xml file. Below is the code for the  information.xml file.

XML

<?xml version="1.0" encoding="utf-8"?>
<users>
    <user>
        <name>Steve</name>
        <designation>Apple</designation>
    </user>
    <user>
        <name>Sundar</name>
        <designation>Google</designation>
    </user>
    <user>
        <name>Jeff</name>
        <designation>Amazon</designation>
    </user>
</users>

Step 3: Working with the activity_main.xml file

Now go to the activity_main.xml file which represents the UI of the application. Create a ListView as shown. Below is the code for the activity_main.xml file.

XML

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="fill_parent"
    android:layout_height="fill_parent"
    android:orientation="vertical">

    <!--ListView to display the list-->
    <ListView
        android:id="@+id/user_list"
        android:layout_width="fill_parent"
        android:layout_height="wrap_content"
        android:dividerHeight="1dp" />
</LinearLayout>

Step 4: Create another layout file

Go to app > res > layout > right-click > New > Layout Resource File and name the file as list. list.xml file is used to show the data in the ListView. Below is the code for the list.xml file.

XML

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="fill_parent"
    android:layout_height="wrap_content"
    android:orientation="horizontal"
    android:padding="5dip">

    <!--textView to show the name node-->
    <TextView
        android:id="@+id/name"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:textSize="17dp"
        android:textStyle="bold" />

    <!--textView to show the designation node-->
    <TextView
        android:id="@+id/designation"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_below="@id/name"
        android:layout_marginTop="7dp"
        android:textColor="#343434"
        android:textSize="14dp" />

</RelativeLayout>

Step 5: Working with the MainActivity.kt file

Finally, go to the MainActivity.kt file, and refer to the following code. Below is the code for the MainActivity.kt file. Comments are added inside the code to understand the code in more detail.

Kotlin

import android.os.Bundle
import android.widget.ListAdapter
import android.widget.ListView
import android.widget.SimpleAdapter
import androidx.appcompat.app.AppCompatActivity
import org.w3c.dom.Document
import org.w3c.dom.Element
import org.w3c.dom.Node
import org.w3c.dom.NodeList
import org.xml.sax.SAXException
import java.io.IOException
import java.io.InputStream
import javax.xml.parsers.DocumentBuilder
import javax.xml.parsers.DocumentBuilderFactory
import javax.xml.parsers.ParserConfigurationException

open class MainActivity : AppCompatActivity() {
    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)

        // Try and Catch for avoiding the application to crash
        try {

            // This list will contain the data from the information.xml file
            val userList: ArrayList<HashMap<String, String?>> = ArrayList()

            // This listView will display the data from the information.xml file
            val lv = findViewById<ListView>(R.id.user_list)

            // The information.xml file will be taken in the form of input stream
            val istream: InputStream = assets.open("information.xml")

            // Steps to convert this input stream into a list
            val builderFactory: DocumentBuilderFactory = DocumentBuilderFactory.newInstance()
            val docBuilder: DocumentBuilder = builderFactory.newDocumentBuilder()
            val doc: Document = docBuilder.parse(istream)
            val nList: NodeList = doc.getElementsByTagName("user")

            // Iterating through this list
            for (i in 0 until nList.length) {
                if (nList.item(0).nodeType === Node.ELEMENT_NODE) {
                    val user: HashMap<String, String?> = HashMap()
                    val elm: Element = nList.item(i) as Element
                    user["name"] = getNodeValue("name", elm)
                    user["designation"] = getNodeValue("designation", elm)
                    userList.add(user)
                }
            }

            // Using Adapter to broadcast the information extracted
            val adapter: ListAdapter = SimpleAdapter(
                this,
                userList,
                R.layout.list,
                arrayOf("name", "designation"),
                intArrayOf(R.id.name, R.id.designation)
            )
            lv.adapter = adapter
        } catch (e: IOException) {
            e.printStackTrace()
        } catch (e: ParserConfigurationException) {
            e.printStackTrace()
        } catch (e: SAXException) {
            e.printStackTrace()
        }
    }

    // A function to get the node value while parsing
    private fun getNodeValue(tag: String?, element: Element): String? {
        val nodeList = element.getElementsByTagName(tag)
        val node = nodeList.item(0)
        if (node != null) {
            if (node.hasChildNodes()) {
                val child = node.firstChild
                while (child != null) {
                    if (child.nodeType == Node.TEXT_NODE) {
                        return child.nodeValue
                    }
                }
            }
        }
        // Returns nothing if nothing was found
        return ""
    }
}

Output: Run on Emulator