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XML Tutorial
XML Parser
By IncludeHelp Last updated : December 29, 2024
What is an XML Parser?
An XML parser is a software library or tool that reads XML documents and provides a structured representation, allowing programs to interact with the data. It ensures that the document is well-formed and validates its structure against predefined rules (if applicable).
Types of XML Parsers
There are two primary types of XML parsers:
- DOM (Document Object Model) Parser
- SAX (Simple API for XML) Parser
Let's explore these in detail.
1. DOM (Document Object Model) Parser
The DOM parser reads the entire XML document into memory and creates a tree structure that can be traversed and manipulated. This makes it ideal for scenarios requiring random access to XML elements.
Features of DOM Parser
- Creates a tree-based structure in memory.
- Supports both reading and writing operations.
- Simple and intuitive API.
Advantages
- Easy to use for small XML documents.
- Enables random access to different parts of the document.
Disadvantages
- Memory-intensive as the entire document is loaded into memory.
- Not suitable for very large XML files.
2. SAX (Simple API for XML) Parser
SAX is an event-driven parser that reads XML data sequentially. Unlike DOM, it does not load the entire document into memory.
Features of SAX Parser
- Event-based parsing (e.g., start and end tags).
- Does not create a tree structure in memory.
Advantages
- Memory efficient as it processes data on-the-fly.
- Suitable for large XML files.
Disadvantages
- Does not allow random access to data.
- Complex implementation for certain tasks.
Parsing XML with JavaScript
Modern web browsers provide built-in support for parsing XML documents using JavaScript. Below are examples demonstrating how to work with XML using the DOMParser and XMLHttpRequest objects.
Example 1: Parsing an XML String
This example demonstrates how to parse a string containing XML data into an XML DOM object and extract information from it.
<!DOCTYPE html>
<html>
<body>
<p id="demo"></p>
<script>
var text, parser, xmlDoc;
text = `
<library>
<book>
<title>Introduction to AI</title>
<author>Amitabh Sharma</author>
<year>2021</year>
</book>
<book>
<title>Data Structures</title>
<author>Rajesh Verma</author>
<year>2018</year>
</book>
</library>`;
parser = new DOMParser();
xmlDoc = parser.parseFromString(text, "text/xml");
document.getElementById("demo").innerHTML =
xmlDoc.getElementsByTagName("title")[0].childNodes[0].nodeValue;
</script>
</body>
</html>
Explanation
- Define XML Data: The text variable holds an XML string.
- Parse the String: Use
DOMParser to convert the string into an XML DOM object.
- Extract Data: Access specific elements (e.g.,
<title>) using getElementsByTagName.
Example 2: Using XMLHttpRequest
This example demonstrates how to fetch and parse an external XML file using XMLHttpRequest:
<!DOCTYPE html>
<html>
<body>
<p id="demo"></p>
<script>
var xmlhttp = new XMLHttpRequest();
xmlhttp.onreadystatechange = function() {
if (this.readyState == 4 && this.status == 200) {
var xmlDoc = this.responseXML;
var output = "";
var books = xmlDoc.getElementsByTagName("book");
for (var i = 0; i < books.length; i++) {
var title = books[i].getElementsByTagName("title")[0].childNodes[0].nodeValue;
var author = books[i].getElementsByTagName("author")[0].childNodes[0].nodeValue;
output += "<b>Title:</b> " + title + "<br><b>Author:</b> " + author + "<br><br>";
}
document.getElementById("demo").innerHTML = output;
}
};
xmlhttp.open("GET", "books.xml", true);
xmlhttp.send();
</script>
</body>
</html>
books.xml
<library>
<book>
<title>Advanced Mathematics</title>
<author>Kavita Das</author>
</book>
<book>
<title>Machine Learning</title>
<author>Vikram Patel</author>
</book>
</library>
Explanation
- Send Request: Use
XMLHttpRequest to fetch the XML file.
- Parse Response: Access the
responseXML property to get the XML DOM object.
- Extract Data: Loop through
<book> elements and extract titles and authors.