使java程序只運行一次，既只允許一個實例保留在內存中

主要是利用fileLock類來實現對文件加鎖，實現上述目的(多說無益，代碼如下):

package com.neonway.oneinstance;

import java.io.*;

import java.nio.channels.*;

public class OneInstance {
??? /**
???? * @param args
???? */
??? public static void main(String[] args) {
??? ?try {

??????????? System.out.println("progran start ...");

??????????? String filename = new String("test.txt");

??????????? File testFile = new File(filename);
??????????? RandomAccessFile raf;
??????????? FileChannel fc;
??????????? FileLock fl;

??????????? testFile.createNewFile();

??????????? if (testFile.canWrite()) {
??????????????? raf = new RandomAccessFile(testFile, "rw");
??????????????? fc = raf.getChannel();
??????????????? fl = fc.tryLock();

??????????????? if ((fl == null) || (fl.isValid() == false)) {
??????????????????? System.out.println("this is useing by another program!");
??????????????? } else {
??????????????? ?System.out.println("program running...");
??????????????????? Thread.sleep(30 * 1000);
??????????????????? fl.release();
??????????????? }

??????????????? raf.close();
??????????? }
?????????? System.out.println("program end ...");
??} catch (Exception e) {
???e.printStackTrace();
??}
??? }
}