Introduction

In the world of mobile applications, data exchange is pivotal. XML (eXtensible Markup Language) is a widely used format for sharing structured data on the internet. As an Android developer, you might encounter XML data frequently, especially when communicating with web services or handling configuration files.

This tutorial focuses on XML parsing in Android using the DOM (Document Object Model) parser. Understanding how to parse XML is essential for handling data efficiently in your applications, whether you're displaying data from a web service or reading configuration settings.

Why Use DOM Parser?

The DOM parser reads the entire XML document into memory as a tree structure. This allows you to navigate and manipulate the XML data easily. However, it can consume more memory due to the complete loading of the document, making it less suitable for very large XML files. Still, for moderate-sized XML files, the DOM parser is intuitive and convenient.

When to Use DOM Parser:

✅ When the XML file is relatively small.
✅ When you require random access to the data.
✅ When data manipulation (like adding, deleting nodes) is necessary.

Concept Explanation

Think of XML as a structured way of representing information, similar to how you might organize a bookshelf. Each book (or node) has a title (tag) and content (value). A DOM parser allows you to load all the books into memory, so you can easily find, read, or modify any book whenever you want.

Comparison with Other Parsers

Feature	DOM Parser	SAX Parser	XMLPullParser
Memory Usage	High (entire document)	Low (event-based)	Low (event-based)
Speed	Slower for large files	Faster for large files	Fast and efficient
Ease of Use	Easier for manipulation	More complex	Flexible but requires manual handling
Suitable for	Small to medium XML files	Large XML files	Streaming data

Syntax Section

To use the DOM Parser in Android, you primarily need to work with the following classes:

✅ DocumentBuilderFactory
✅ DocumentBuilder
✅ Document
✅ Element
✅ Node

Basic Syntax

Here’s a simplified step-by-step breakdown of the syntax to parse XML using a DOM parser:

Example


// Step 1: Create a DocumentBuilderFactory instance
val factory = DocumentBuilderFactory.newInstance()

// Step 2: Create a DocumentBuilder
val builder = factory.newDocumentBuilder()

// Step 3: Parse the XML file to create a Document object
val document = builder.parse(inputStream)

// Step 4: Access elements using document methods
val nodeList = document.getElementsByTagName("tagName")

Working Examples

Example 1: Basic XML Parsing

Let’s start with a simple XML file and parse it to retrieve employee names.

XML File (employees.xml)

Example


<employees>
    <employee>
        <name>John Doe</name>
    </employee>
    <employee>
        <name>Jane Smith</name>
    </employee>
</employees>

Kotlin Code:

Example


import android.os.Bundle
import android.support.v7.app.AppCompatActivity
import org.w3c.dom.Element
import org.w3c.dom.Node
import javax.xml.parsers.DocumentBuilderFactory

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

        val inputStream = assets.open("employees.xml")
        val factory = DocumentBuilderFactory.newInstance()
        val builder = factory.newDocumentBuilder()
        val document = builder.parse(inputStream)

        val employeeNodes = document.getElementsByTagName("employee")
        for (i in 0 until employeeNodes.length) {
            val element = employeeNodes.item(i) as Element
            val name = getNodeValue("name", element)
            println("Employee Name: $name")
        }
    }

    private fun getNodeValue(tag: String, element: Element): String {
        return element.getElementsByTagName(tag).item(0).textContent
    }
}

Output:

Output


Employee Name: John Doe
Employee Name: Jane Smith

Example 2: Parsing Employee Details

Let’s extend our XML to include more details about employees.

XML File (empdetails.xml)

Example


<employees>
    <employee>
        <name>John Doe</name>
        <salary>50000</salary>
        <designation>Developer</designation>
    </employee>
    <employee>
        <name>Jane Smith</name>
        <salary>60000</salary>
        <designation>Manager</designation>
    </employee>
</employees>

Kotlin Code:

Example


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

        val inputStream = assets.open("empdetails.xml")
        val factory = DocumentBuilderFactory.newInstance()
        val builder = factory.newDocumentBuilder()
        val document = builder.parse(inputStream)

        val employeeNodes = document.getElementsByTagName("employee")
        for (i in 0 until employeeNodes.length) {
            val element = employeeNodes.item(i) as Element
            val name = getNodeValue("name", element)
            val salary = getNodeValue("salary", element)
            val designation = getNodeValue("designation", element)

            println("Employee Name: $name, Salary: $salary, Designation: $designation")
        }
    }

    private fun getNodeValue(tag: String, element: Element): String {
        return element.getElementsByTagName(tag).item(0).textContent
    }
}

Output:

Output


Employee Name: John Doe, Salary: 50000, Designation: Developer
Employee Name: Jane Smith, Salary: 60000, Designation: Manager

Example 3: Displaying Data in a ListView

Now, let’s display the parsed employee details in a ListView.

Layout (activity_main.xml)

Example


<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical">
    <ListView
        android:id="@+id/listView"
        android:layout_width="match_parent"
        android:layout_height="wrap_content" />
</LinearLayout>

Kotlin Code:

Example


import android.os.Bundle
import android.widget.ListView
import android.widget.SimpleAdapter
import android.support.v7.app.AppCompatActivity
import org.w3c.dom.Element
import javax.xml.parsers.DocumentBuilderFactory

class MainActivity : AppCompatActivity() {
    private lateinit var employeeList: ArrayList<HashMap<String, String>>

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

        employeeList = ArrayList()
        val inputStream = assets.open("empdetails.xml")
        val factory = DocumentBuilderFactory.newInstance()
        val builder = factory.newDocumentBuilder()
        val document = builder.parse(inputStream)

        val employeeNodes = document.getElementsByTagName("employee")
        for (i in 0 until employeeNodes.length) {
            val element = employeeNodes.item(i) as Element
            val employeeData = HashMap<String, String>()
            employeeData["name"] = getNodeValue("name", element)
            employeeData["salary"] = getNodeValue("salary", element)
            employeeData["designation"] = getNodeValue("designation", element)
            employeeList.add(employeeData)
        }

        val listView = findViewById<ListView>(R.id.listView)
        val adapter = SimpleAdapter(this, employeeList, android.R.layout.simple_list_item_2,
            arrayOf("name", "salary"),
            intArrayOf(android.R.id.text1, android.R.id.text2))
        listView.adapter = adapter
    }

    private fun getNodeValue(tag: String, element: Element): String {
        return element.getElementsByTagName(tag).item(0).textContent
    }
}

Output:

✅ The ListView displays the names and salaries of employees.

Common Mistakes

✅ Not Closing Input Streams: Always ensure that you close your input streams to avoid memory leaks.
✅ Incorrect Tag Names: When accessing XML nodes, ensure that the tag names used in the code exactly match those in the XML file.
✅ Null Pointer Exceptions: Always check for null when retrieving node values, especially when working with optional elements.

Best Practices

✅ Use Meaningful Variable Names: This helps in code readability and maintainability.
✅ Error Handling: Always implement error handling when parsing XML, such as try-catch blocks for IOException and ParserConfigurationException.
✅ Optimize Memory Usage: Consider using SAX or XMLPullParser for larger XML files to avoid high memory usage.

Practice Exercises

Create Your Own XML File: Design an XML file similar to the provided examples but include additional details like age and department. Write code to parse and display this data in a ListView.
Modify Parsing Logic: Enhance the existing parsing logic to filter employees based on a specific criterion, such as salary or designation.
XML File from URL: Modify the code to fetch an XML file from a URL instead of local assets. Implement error handling for network requests.

By practicing these exercises, you'll reinforce your understanding of XML parsing in Kotlin and Android. Happy coding!

Dom Parser

Introduction

Why Use DOM Parser?

When to Use DOM Parser:

Concept Explanation

Comparison with Other Parsers

Syntax Section

Basic Syntax

Working Examples

Example 1: Basic XML Parsing

Example 2: Parsing Employee Details

Example 3: Displaying Data in a ListView

Common Mistakes

Best Practices

Practice Exercises

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Introduction

Why Use DOM Parser?

When to Use DOM Parser:

Concept Explanation

Comparison with Other Parsers

Syntax Section

Basic Syntax

Working Examples

Example 1: Basic XML Parsing

Example 2: Parsing Employee Details

Example 3: Displaying Data in a ListView

Common Mistakes

Best Practices

Practice Exercises

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Hi! I'm your coding mentor