原理:
JDK的nio包中FileLock实现类似Linux fcntl的文件锁, 可使文件被进程互斥访问.  借助此功能, 可以实现强大的Java进程互斥锁, 从而在应用层面保证同一时间只有惟一的Jar应用进程在运行! 避免某些因素导致jar重复执行, 多个进程产生竞争,破坏业务数据. (当然, 你可以借助类似ubuntu的upstart脚本或者ps -p <pid>之类的做法来做到相同的功能).
实现:

1. package test;
2. import java.io.File;
3. import java.io.IOException;
4. import java.io.RandomAccessFile;
5. import java.nio.channels.FileChannel;
6. import java.nio.channels.FileLock;
7. import java.util.concurrent.Callable;
8. import java.util.concurrent.TimeUnit;
9. public class FileLockTest {
10.         public static void main(String[] args) throws Exception {
11.                 exclusiveWithFileLock(new Callable<Void>() {
12.                         @Override
13.                         public Void call() throws Exception {
14.                                 TimeUnit.SECONDS.sleep(10); // 使用休眠模拟业务逻辑
15.                                 return null;
16.                         }
17.                 });
18.         }
19.         public static <V> V exclusiveWithFileLock(Callable<V> caller)
20.                         throws Exception {
21.                 File lockFile = new File("/tmp/"+FileLockTest.class.getCanonicalName());//使用类名做为文件名称
22.                 if (!lockFile.exists()) {
23.                         if (!lockFile.getParentFile().exists()) {
24.                                 lockFile.getParentFile().mkdirs();
25.                         }
26.                         if (!lockFile.createNewFile()) {
27.                                 throw new IOException("create lock file failed! ");
28.                         }
29.                 }
30.                 FileChannel fc = null;
31.                 try {
32.                         fc = new RandomAccessFile(lockFile,"rw").getChannel();
33.                         FileLock lck = fc.tryLock();
34.                         if (lck == null) {
35.                                 System.out.println("File is lock by another programme");
36.                                 System.exit(1);
37.                         } else {
38.                                 System.out.println("Do your work here...");
39.                                 return caller.call();
40.                         }
41.                 } finally {
42.                         if (fc != null) {
43.                                 fc.close();
44.                         }
45.                 }
46.                 return null;
47.         }
48. }

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结果:

1. xuser@pc120:~/myworkspace/source/jademo/src$ java test.FileLockTest
2. File is lock by another programme
3. xuser@pc120:~/myworkspace/source/jademo/src$ java test.FileLockTest
4. Do your work here...

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优势:
1. 实现简单, 功能强大.

Java使用FileLock实现Java进程互斥锁