One problem, however, is that you need to have JRE 6 installed. Previous versions of Java VM do not support System Tray.

Creating SystemTray Icon

Firstly, we need to have the following packages imported:

import java.awt.SystemTray;
import java.awt.TrayIcon;
import java.awt.TrayIcon.MessageType;

Let's declare a SystemTray variable

TrayIcon trayIcon = null;

Then we need to check if the SystemTray is supported.

if (SystemTray.isSupported()) ...

If it is, then we will create a new TrayIcon. To create the TrayIcon we need to specify the Icon (or you can use the standard Java Icon), application name and a PopupMenu to be shown on right click.

// getting image to be used as icon for our TrayIcon

URL iconURL = getClass().getResource("/graphics/rss.png");
ImageIcon icon = new ImageIcon(iconURL);

// Creating popup menu to be shown on right click
trayMenu = new PopupMenu();
// Shows or hides main frame
popupShowHide = new MenuItem("Show/Hide");
popupShowHide.addActionListener(new ActionListener() {
  public void actionPerformed(ActionEvent event) {
   frame.setVisible(!frame.isVisible());
  }
});
 trayMenu.add(popupShowHide);
// close application
 MenuItem popupExit = new MenuItem("Exit");
 popupExit.addActionListener(new ActionListener() {
 public void actionPerformed(ActionEvent event) {
 closeApplication();
 }
 });
 trayMenu.add(popupExit);

// Create TrayIcon
trayIcon = new TrayIcon(icon.getImage(), // Image
"My Application", // Caption Text
trayMenu // Popup Menu
);
// shrink image to the size of the tray icon
trayIcon.setImageAutoSize(true);

// instance of SystemTray
SystemTray systemTray = SystemTray.getSystemTray();

// trying to add the TrayIcon
try {
 systemTray.add(trayIcon);
} catch (AWTException ignore) {
 // ignore
}

Also, you can catch the left double click on the TrayIcon. Say, for example you want to activate your application on left double click. Just add and ActionListener like this.

trayIcon.addActionListener(new ActionListener() {
 public void actionPerformed(ActionEvent event) {
  frame.setVisible(!frame.isVisible());
 }
});

SystemTray notifications

SystemTray allows you to show notifications about some events that has occured.

public void showInformation(String message) {

 trayIcon.displayMessage("My Application", // Application Title
 message, // Message to be shown
 MessageType.INFO // Type of the message - INFO
 );

}

For more information visit java.sun.com website.

Reading XML files

Example XML file: channels.xml

<?xml version="1.0" encoding="UTF-8" standalone="no"?>
<channels>
 <channel>
  <url>http://rss.dw-world.de/rdf/rss-en-world</url>
  <title>Deutsche Welle: DW-WORLD.DE - World</title>
  <updatestatus>OK</updatestatus>
  <updatetime>29.7.2009 21:41:16</updatetime>
 </channel>
 <channel>
  <url>http://rss.dw-world.de/rdf/rss-en-eu</url>
  <title>Deutsche Welle: DW-WORLD.DE - Europe</title>
  <updatestatus>OK</updatestatus>
  <updatetime>29.7.2009 21:41:15</updatetime>
 </channel>
</channels>

This is a configuration file that is used to store RSS channels. Each channel is represented by the Channel object that are stored in the channel ArrayList. When the application starts it parses the configuration file channels.xml and fills ArrayList<Channel> with Channel entities. This short tutorial is not about Collections, but there will be some extra code to make this example more interesting.

I use DocumentBuilder class to create DOM structure from XML. The DocumentBuilder is in javax.xml package, so to use it you need to have the following packages imported.

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

The following code parses an XML file and loads the configuration.

// configuration XML file to store channels
File channelsFile = new File(userHomeDir + fileSeparator + programDirName +
                    fileSeparator + "channels.xml");

try {

// getting the instance of the DocumentBuilderFactory
DocumentBuilderFactory dbf = DocumentBuilderFactory.newInstance();
// call factory method to get a new Document Builder instance
DocumentBuilder db = dbf.newDocumentBuilder();

// trying to parse the file
Document doc = db.parse(channelsFile);
// normalizing a file to merge all text nodes
doc.getDocumentElement().normalize();

// getting the list of <channel> nodes
NodeList nodeList = doc.getElementsByTagName("channel");

// loop through the node list
for (int i = 0; i < nodeList.getLength(); i++) {
// getting a node
Node channelNode = nodeList.item(i);

// an element found?
if (channelNode.getNodeType() == Node.ELEMENT_NODE) {

// strings to store values
String channelUrl = "";
String channelTitle = "";

// convert node to element
Element channelElement = (Element) channelNode;

// get Channel Url
NodeList channelUrlList = channelElement.getElementsByTagName("url");
Element channelUrlElement = (Element) channelUrlList.item(0);
NodeList channelUrlTextList = channelUrlElement.getChildNodes();
channelUrl = ((Node) channelUrlTextList.item(0)).getNodeValue().trim();

// getting the remaining parameters
// ...

// create a Channel instance
Channel aChannel = new Channel(channelUrl);
// configure the instance
aChannel.setName(channelTitle);

// add new Channel to ArrayList
channelList.add(aChannel);

} catch (Exception e) {

// catch exceptions ...
e.printStackTrace();

}