Reading/Writing Settings to Xml in Java

Posted on: November 26th, 2009

Tags: configuration, readXml, Serialization, settings, writeXml

Here’s an easy way to store and retrieve settings or other data from an Xml file.All the settings is set by key/value pairs in an XML file, you can insert and retrieve any key/value. The two major public methods are: get(key,default) and put(key,value) – it’s that simple. You can store String, Integer and Boolean Datatypes.

Here’s how to use the class:

Xml xml = new Xml(System.getProperty("user.home") + "/config.xml","configuration"); // first parameter = xmlFile; second parameter = configuration name
xml.get("key1", "xxx"); // returns xxx if no value is set
xml.get("key2", 11); // the same with an Integer
xml.get("key3", true); // the same with a Boolean Type

xml.put("key4", 5); // stores the value 5
xml.get("key4", 20); // returns 5

xml.writeXml(); // Save all changes

Here’s the main Class:

import java.io.File;
import org.w3c.dom.*;
import javax.xml.parsers.*;
import javax.xml.transform.*;
import javax.xml.transform.stream.*;
import javax.xml.transform.dom.*;

/**
*
* @author simon
*/
public class Xml {

private File _xmlFile;
private Element _config;
private Document _dom;

public Xml(String file, String config) {
_xmlFile = new File(file);
readXml();
_config = getConfigElement(config);
}

public Object get(String key, Object def) {
Element e = getElement(key);
if(e.getChildNodes().getLength()==0){
return def;
}

String type = e.getAttribute("type");
String value = e.getChildNodes().item(0).getNodeValue();

if(type.indexOf("Integer")>=0){
return Integer.parseInt(value);
}else if(type.indexOf("Boolean")>=0){
return value.equals("true");
}
return value;
}

public void put(String key, Object value) {
Element e = getElement(key);
e.getNodeValue();
if(e.getChildNodes().getLength()>0){
e.removeChild(e.getChildNodes().item(0));
}
Node n = _dom.createTextNode(value.toString());
e.appendChild(n);
e.setAttribute("type", value.getClass().getName());
}

public boolean writeXml() {
try {
Source source = new DOMSource(_dom);
Result result = new StreamResult(_xmlFile);
Transformer xformer = TransformerFactory.newInstance().newTransformer();
xformer.transform(source, result);
return true;
} catch (Exception ex) {
}
return false;
}

private Element getElement(String key) {
NodeList nl = _config.getElementsByTagName(key);
Element e;
if (nl != null && nl.getLength() > 0) {
e = (Element) nl.item(0);
} else {
//append element if not exists
e = _dom.createElement(key);
_config.appendChild(e);
}
return e;
}

private Element getConfigElement(String config) {
Element root = _dom.getDocumentElement();
NodeList nl = root.getElementsByTagName(config);
Element e;
if (nl != null && nl.getLength() > 0) {
e = (Element) nl.item(0);
} else {
//append config if not exists
e = _dom.createElement(config);
root.appendChild(e);
}
return e;
}

private boolean readXml() {
if (_xmlFile.isFile()) {
DocumentBuilderFactory dbf = DocumentBuilderFactory.newInstance();
try {
DocumentBuilder db = dbf.newDocumentBuilder();
_dom = db.parse(_xmlFile);
return true;
} catch (Exception ex) {
}
} else {
try {
DocumentBuilderFactory factory = DocumentBuilderFactory.newInstance();
DocumentBuilder builder = factory.newDocumentBuilder();
DOMImplementation impl = builder.getDOMImplementation();
_dom = impl.createDocument(null, "Root", null);
return true;
} catch (ParserConfigurationException ex) {
}
}
return false;
}
}

That’s what the Xml File looks like after saving: