Java XML Parsing Tutorial: DOM

As the whole document is stored in memory at once, it is preferred for only small documents.

• It is a tree model parser (Object-based).
• First, it loads the file into the memory and then parses the file.
• It has memory constraints since it loads the whole XML file before parsing.
• It supports both read and write operations.
• Backward and forward searches are possible for searching the tags and evaluating the information inside the tags.
• It is slower at run time.

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Content of Employee.java

package com.t4b.parser.dom.test; public class Employee { private String name; private int age; private int id; private String type; public Employee(String name, int id, int age, String type) { this.name = name; this.age = age; this.id = id; this.type = type; } public int getAge() { return age; } public void setAge(int age) { this.age = age; } public int getId() { return id; } public void setId(int id) { this.id = id; } public String getName() { return name; } public void setName(String name) { this.name = name; } public String getType() { return type; } public void setType(String type) { this.type = type; } public String toString() { StringBuffer sb = new StringBuffer(); sb.append("Employee Details - "); sb.append("Name:" + getName()); sb.append(", "); sb.append("Type:" + getType()); sb.append(", "); sb.append("Id:" + getId()); sb.append(", "); sb.append("Age:" + getAge()); sb.append("."); return sb.toString(); } }

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Content of DomParserTest.java

package com.t4b.parser.dom.test; import java.io.IOException; import java.util.ArrayList; import java.util.Iterator; import java.util.List; import javax.xml.parsers.DocumentBuilder; import javax.xml.parsers.DocumentBuilderFactory; import javax.xml.parsers.ParserConfigurationException; import org.w3c.dom.Document; import org.w3c.dom.Element; import org.w3c.dom.NodeList; import org.xml.sax.SAXException; public class DomParserTest { List<Employee> myEmpls; Document dom; public DomParserTest() { myEmpls = new ArrayList<Employee>(); } public void runExample(String filename) { parseXmlFile(filename); parseDocument(); printData(); } private void parseXmlFile(String filename) { DocumentBuilderFactory dbf = DocumentBuilderFactory.newInstance(); try { DocumentBuilder db = dbf.newDocumentBuilder(); dom = db.parse(filename); } catch (ParserConfigurationException pce) { pce.printStackTrace(); } catch (SAXException se) { se.printStackTrace(); } catch (IOException ioe) { ioe.printStackTrace(); } } private void parseDocument() { Element docEle = dom.getDocumentElement(); NodeList nl = docEle.getElementsByTagName("Employee"); if (nl != null && nl.getLength() > 0) { for (int i = 0; i < nl.getLength(); i++) { Element el = (Element) nl.item(i); Employee e = getEmployee(el); myEmpls.add(e); } } } private Employee getEmployee(Element empEl) { String name = getTextValue(empEl, "Name"); int id = getIntValue(empEl, "Id"); int age = getIntValue(empEl, "Age"); String type = empEl.getAttribute("type"); Employee e = new Employee(name, id, age, type); return e; } private String getTextValue(Element ele, String tagName) { String textVal = null; NodeList nl = ele.getElementsByTagName(tagName); if (nl != null && nl.getLength() > 0) { Element el = (Element) nl.item(0); textVal = el.getFirstChild().getNodeValue(); } return textVal; } private int getIntValue(Element ele, String tagName) { return Integer.parseInt(getTextValue(ele, tagName)); } private void printData() { System.out.println("No of Employees '" + myEmpls.size() + "'."); Iterator<Employee> it = myEmpls.iterator(); while (it.hasNext()) { System.out.println(it.next().toString()); } } public static void main(String[] args) { DomParserTest dpt = new DomParserTest(); dpt.runExample("employees.xml"); } }

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Content of employees.xml document for parsing

<?xml version="1.0" encoding="UTF-8"?> <Personnel> <Employee type="permanent"> <Name>John</Name> <Id>1000</Id> <Age>34</Age> </Employee> <Employee type="contract"> <Name>Robin</Name> <Id>1001</Id> <Age>25</Age> </Employee> <Employee type="permanent"> <Name>Neil</Name> <Id>1002</Id> <Age>26</Age> </Employee> </Personnel>

Happy Exploring!