Shared File Lock

import java.io.File;
import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.RandomAccessFile;
import java.nio.channels.FileChannel;
import java.nio.channels.FileLock;
import java.nio.charset.StandardCharsets;
import java.nio.file.Files;
import java.util.Arrays;

public class SomeClass {
  public static void main(final String[] args) throws Exception {
    final File file = File.createTempFile("SharedLockDemo", ".tmp");
    try (FileOutputStream fs = new FileOutputStream(file)) {
      fs.write("HELLO".getBytes(StandardCharsets.US_ASCII));
    }

    if (!file.exists())
      throw new FileNotFoundException();
    try (final RandomAccessFile raf = new RandomAccessFile(file, "r");
        FileChannel channel = raf.getChannel()) {
      // Must be shared, since we are only in read access mode.
      final FileLock lock = channel.lock(0, Long.MAX_VALUE, true);
      final long size = channel.size();
      System.out.println("Size: " + size); // should be |HELLO| = 5

      final String[] commands = new String[3];
      commands[0] = "CMD"; // CMD startet echten neuen Prozess
      commands[1] = "/C"; // Führt folgende Befehle aus:
      commands[2] = "ECHO BOGUS > \"" + file.getCanonicalPath()
          + "\" || EXIT 1"; // String Ausgabe

      System.out.println("Commands: " + Arrays.toString(commands));
      // Befehl ausführen:
      final Process process = Runtime.getRuntime().exec(commands);
      final int exitValue = process.waitFor();
      // I'd expect the value to be 1.
      System.out.println("Exit Value: " + exitValue);

      lock.release();

      System.out.println("Contents of file:");
      final byte[] contents = Files.readAllBytes(file.toPath());
      if (contents.length == 0)
        System.out.println("<EMPTY>");
      else
        System.out.println(new String(contents, StandardCharsets.US_ASCII));
    }

  }

/* OUTPUT (Windows 7, Java 8):

Size: 5
Commands: [CMD, /C, ECHO BOGUS > "C:\Users\Claude\AppData\Local\Temp\SharedLockDemo4948636556524834177.tmp" || EXIT 1]
Exit Value: 0
Contents of file:
<EMPTY>

*/

}