[roots]

import java.io.FileInputStream;
import java.util.ArrayList;
import java.util.Iterator;
import java.util.List;

import org.xml.sax.Attributes;
import org.xml.sax.InputSource;
import org.xml.sax.SAXException;
import org.xml.sax.XMLReader;
import org.xml.sax.helpers.DefaultHandler;
import org.xml.sax.helpers.XMLReaderFactory;

public class EmployeeXMLHandler extends DefaultHandler {

	private List<EmployeeNode> employees = new ArrayList<EmployeeNode>();
	private EmployeeNode currentEmployeeNode; // Used in XML Processing only

	public EmployeeXMLHandler() {}
	
	
	private String characterChunk = "" ;
	@Override
	public void characters(char[] ch, int start, int length)
			throws SAXException {
		// We can not be sure that all character will be passed on single call .. 
		characterChunk = characterChunk + new String(ch,start,length);
	}
	
	@Override
	public void startElement(String uri, String localName, String name,
			Attributes attributes) throws SAXException {
		characterChunk = "";
		if (name.equalsIgnoreCase("res_mesg")) {
			// create a new instance of employee
			currentEmployeeNode = new EmployeeNode();
			for (int len = 0; len < attributes.getLength(); len++) {
				currentEmployeeNode.setCategory(attributes.getValue("category"));
			}
		}
	}
	
	@Override
	public void endElement(String uri, String localName, String name)
			throws SAXException {
		if (name.equalsIgnoreCase("res_mesg")) {
			employees.add(currentEmployeeNode);
		} else if (name.equalsIgnoreCase("res_no")) {
			currentEmployeeNode.addResNo(characterChunk);
		}
	}
	
	public void print(){
		Iterator<EmployeeNode> iterator = employees.iterator();
		while(iterator.hasNext()){
			System.out.println(iterator.next());
		}
	}
	
	public List<EmployeeNode> getEmployees(){
		return this.employees; 
	}	
	
	public void process()throws Exception{
		XMLReader reader = XMLReaderFactory.createXMLReader();		
		reader.setContentHandler(this);
		reader.parse(new InputSource(new FileInputStream("data.xml")));
		print();
		
	}
	
	public static void main(String[] args) throws Exception {
		new EmployeeXMLHandler().process();
	}
	
	/**
	 * Same thing here .. why public static list .. ? 
	 * If you want it to be public static you can change it..
	 */
}

import java.util.ArrayList;
import java.util.Iterator;
import java.util.List;

public class EmployeeNode {
	private List<String> resNo = new ArrayList<String>();
	private String category;

	public String toString() {
		String toStr = "Category = " + category + " & res no = ";

		Iterator<String> iterator = resNo.iterator();
		while (iterator.hasNext()) {
			toStr = toStr + iterator.next() + ",";
		}
		return toStr.substring(0, toStr.length() - 1); // removing last coma
	}

	public List<String> getResNo() {
		return resNo;
	}

	public void setResNo(List<String> resNo) {
		this.resNo = resNo;
	}

	public String getCategory() {
		return category;
	}

	public void setCategory(String category) {
		this.category = category;
	}

	public void addResNo(String data) {
		this.resNo.add(data);
	}

}

Output

Category = 1 & res no = 101,102
Category = 2 & res no = 201,202