Simple XML Validator - The Coding Shala

Home >> Programming Questions >> XML Validator

 In this post, we will are going to implement a Simple XML Validator in the Java language.

Simple XML Validator in Java

The input is an ASCII string, we have to write a Java program to check if the given String is valid XML or not. For simplicity purposes, the XML string only has content and tags.

 The output should be a String for whether the text is valid XML or not. If the XML is invalid, output one of the three error strings:
1. "missing closing tag for <start_tag>"
2. "encountered closing tag without matching open tag for </end tag>"
3. "parse error"

Example 1:
Input: <a>some text</a>
Output: valid

Example 2:
Input: <a>
Output: missing closing tag for <a>

We can use the stack data structure.

Java Program:

class Solution {
	public String validate_xml(String xml) {
		if(xml == null || xml.isEmpty()) return "valid";
		Stack<String> stack = new Stack<>();
		int i = 0;
		while(i < xml.length()) {
			if(xml.charAt(i) == '<') {
				if(i < xml.length() && xml.charAt(i+1) == '/') {
					//closing tag
					i = i+2;
					StringBuilder end = new StringBuilder("<");
					while(xml.charAt(i) != '>') {
						if(xml.charAt(i) == '<') return "parse error";
					if(end.length() == 1) return "parse error";
					if(stack.peek().equals(end.toString())) {
					} else {
						StringBuilder tag = new StringBuilder("</");
						for(int j=1; j<end.length(); j++) {
						return "encountered closing tag without matching open tag for " + tag.toString();
				} else {
					//start tag
					StringBuilder sb = new StringBuilder("<");
					while(xml.charAt(i) != '>') {
						if(xml.charAt(i) == '<') return "parse error";
					if(sb.length() == 1) return "parse error";
		if(!stack.isEmpty()) {
			return "missing closing tag for " + stack.pop();
		return "valid";

Other Posts You May Like
Please leave a comment below if you like this post or found some errors, it will help me to improve my content.


Popular Posts from this Blog

Shell Script to find sum, product and average of given numbers - The Coding Shala

Shell Script to Create a Simple Calculator - The Coding Shala

Add two numbers in Scala - The Coding Shala

New Year Chaos Solution - The Coding Shala

Richest Customer Wealth LeetCode Solution - The Coding Shala