Simple Tail in Java with Shutdownhook

#log

#tools

#hook

#system


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());
 }
}