使用Java NIO 文件锁实现进程独占

代码来自HDFS DataNode中的使用方式...看起来相对容易，实际有几点需要注意，

1.文件一定要deleteOnExit().

2.发生异常一定要将RandoemAccessFile close（）掉.

3.FileLock为null时要判断.

4.FileLock关闭时,先调用FileLock.release(), 而后FileLock.chanel().close();

public class FileLockDemo {
private static final String FILE_LOCK_PATH = "c:" + File.separator;
private static final String FILE_LOCK_FILE_NAME = "in_use.lock";

private FileLock tryLock() throws IOException {
File lockFile = new File(FILE_LOCK_PATH, FILE_LOCK_FILE_NAME);

if(!lockFile.exists()) {
lockFile.deleteOnExit();
}

RandomAccessFile file = new RandomAccessFile(lockFile, "rws");
FileLock fileLock = null;
try {
fileLock = file.getChannel().tryLock();
if(fileLock == null) {
throw new OverlappingFileLockException();
}
} catch (OverlappingFileLockException e) {
file.close();
return null;
}
catch (IOException e) {
file.close();
throw e;
}

file.write(ManagementFactory.getRuntimeMXBean().getName().getBytes("UTF-8"));
lockFile.deleteOnExit();
return fileLock;
}

private void unLock(FileLock fileLock) throws IOException {
if(fileLock == null) {
return;
}
fileLock.release();
fileLock.channel().close();
}

public static void main(String[] args) {
for(int i = 0; i < 10; i++) {
new Thread(new Runnable() {
@Override
public void run() {
try {
FileLockDemo demo = new FileLockDemo();
FileLock fileLock = demo.tryLock();
if(fileLock != null) {
System.out.println(String.format("%s get file lock...",
Thread.currentThread().getName()));
}
else {
System.out.println(String.format("%s can not get file lock...",
Thread.currentThread().getName()));
}
TimeUnit.SECONDS.sleep(30);
demo.unLock(fileLock);
} catch (IOException e) {
e.printStackTrace();
} catch (InterruptedException e) {
e.printStackTrace();
}

}
}).start();
}
}
}