XML Parsing in Android using DOM Parser

23 Feb, 2021
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:
Prolog: The XML file will start with a prolog. Prolog contains the information about a file, which is available in the first line.Events: Events such as document start and end, tag start and end, etc. are contained in the XML fileText: It is a simple text present in between the opening and closing XML tag elements.Attributes: They are the additional properties of a tag present within the label.
Prolog: The XML file will start with a prolog. Prolog contains the information about a file, which is available in the first line.
Events: Events such as document start and end, tag start and end, etc. are contained in the XML file
Text: It is a simple text present in between the opening and closing XML tag elements.
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
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.We want to show this data in the form of a list to implement a list view.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.Using a DocumentBuilderFactory, we would create a new instance.Using a DocumentBuilder, we generate a new document builder.Using a Document method, we parse the input stream.As the information is in the form of nodes, we would create a NodeList and iterate through every node using a FOR loop.Specific information would be extracted in this loop and added to a list (declared earlier in the code).Using a ListAdapter, the data is broadcasted into the list view layout file.
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.
We want to show this data in the form of a list to implement a list view.
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.
Using a DocumentBuilderFactory, we would create a new instance.
Using a DocumentBuilder, we generate a new document builder.
Using a Document method, we parse the input stream.
As the information is in the form of nodes, we would create a NodeList and iterate through every node using a FOR loop.
Specific information would be extracted in this loop and added to a list (declared earlier in the code).
Using a ListAdapter, the data is broadcasted into the list view layout file.
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.Bundleimport android.widget.ListAdapterimport android.widget.ListViewimport android.widget.SimpleAdapterimport androidx.appcompat.app.AppCompatActivityimport org.w3c.dom.Documentimport org.w3c.dom.Elementimport org.w3c.dom.Nodeimport org.w3c.dom.NodeListimport org.xml.sax.SAXExceptionimport java.io.IOExceptionimport java.io.InputStreamimport javax.xml.parsers.DocumentBuilderimport javax.xml.parsers.DocumentBuilderFactoryimport 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 ""    }}
Android-Misc
Android
Kotlin
Android
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