这是一个防止程序运行多次的程序!有几个看不懂!

lirong_wfmall 2007-06-21 10:03:12

为什么这个程序能实现防止运行多次呢?
FileChannel,FileLock 这2个类到底有什么用啊.
文件通道到底是什么东东?

import java.io.File;
import java.io.RandomAccessFile;
import java.nio.channels.FileChannel;
import java.nio.channels.FileLock;
import java.nio.channels.OverlappingFileLockException;
import java.util.RandomAccess;
import javax.swing.JOptionPane;

public class A1 {

private FileChannel channel;//文件通道究竟是什么东西?

private FileLock lock;//还有这个类.

private File file;

public A1(String lockFileName) {
file = new File(lockFileName);
}

public boolean isAppActive() {
try {
channel = new RandomAccessFile(file, "rw").getChannel();
try {
lock = channel.tryLock();

} catch (OverlappingFileLockException e) {
closeLock();
return true;
}
if (lock == null) {
closeLock();
return true;
}
Runtime.getRuntime().addShutdownHook(new Thread() {
public void run() {
closeLock();
deleteFile();
}
});
return false;
} catch (Exception e) {
closeLock();
return true;
}
}

protected void deleteFile() {
try {
file.delete();
} catch (Exception e) {

}

}

private void closeLock() {
try {
lock.release();
} catch (Exception e) {

}

try {
channel.close();
} catch (Exception e) {

}

}

public static void main(String[] args) {
A1 a = new A1(".lock");
if (a.isAppActive() == true)
JOptionPane.showMessageDialog(null, "已有一个程序在运行,程序退出");

try {
Thread.sleep(10000);
} catch (InterruptedException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}

}

}

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