Cola simple en Java con Shutdownhook


import java.io.File;
import java.io.RandomAccessFile;
import java.util.logging.Level;
import java.util.logging.Logger;

/**
* based on http://stackoverflow.com/a/559146/1313040

* also based on http://stackoverflow.com/a/2922031/1313040

*/

public class Tail implements Runnable {

private long _updateInterval = 1000;
private long _filePointer;
private File _file;
private static volatile boolean keepRunning = true;

public static void main(String[] args) {
final Thread mainThread = Thread.currentThread();
Runtime.getRuntime().addShutdownHook(new Thread() {
@Override
public void run() {
keepRunning
= false;
try {
mainThread
.join();
} catch (InterruptedException ex) {
Logger.getLogger(Tail.class.getName()).log(Level.SEVERE, null, ex);
}
}
});
File log = new File("/var/log/system.log");
Tail tail = new Tail(log);
new Thread(tail).start();

}

public Tail(File file) {
this._file = file;
}

@Override
public void run() {
try {

while (keepRunning) {
Thread.sleep(_updateInterval);
long len = _file.length();

if (len < _filePointer) {
// Log must have been jibbled or deleted.
this.appendMessage("Log file was reset. Restarting logging from start of file.");
_filePointer
= len;
} else if (len > _filePointer) {
// File must have had something added to it!
RandomAccessFile raf = new RandomAccessFile(_file, "r");
raf
.seek(_filePointer);
String line = null;
while ((line = raf.readLine()) != null) {
this.appendLine(line);
}
_filePointer
= raf.getFilePointer();
raf
.close();
}
}
} catch (Exception e) {
this.appendMessage("Fatal error reading log file, log tailing has stopped.");
}
// dispose();
}

private void appendMessage(String line) {
System.out.println(line.trim());
}

private void appendLine(String line) {
System.out.println(line.trim());
}
}