java 文件锁的简单实现

import java.io.File; import java.io.FileInputStream; import java.io.FileNotFoundException; import java.io.IOException; import java.io.InputStreamReader; import java.io.RandomAccessFile; import java.nio.channels.FileChannel; import java.nio.channels.FileLock; public class FileLocker {   public static void main(String[] args) throws IOException {     File f = new File("aaa.txt");     System.out.println(getFileContent(f) + 1);// no lock     FileLock lock = getFileLock(f);// lock     System.out.println(getFileContent(f) + 2);     lock.release();// lock release     System.out.println(getFileContent(f) + 3);// no lock   }   /**    * get file content.    *    * @param file    * @return    */   public static String getFileContent(File file) {     String line = "";     String content = "";     try {       BufferedReader bf = new BufferedReader(new InputStreamReader(           new FileInputStream(file)));       while ((line = bf.readLine()) != null) {         content += line;       }     } catch (FileNotFoundException e) {       content = "ERROR ";     } catch (IOException e) {       content = "ERROR ";     }     return content;   }   /**    * get lock.    *    * @param file    * @return    * @throws IOException    */   public static FileLock getFileLock(File file) throws IOException {     RandomAccessFile fi = new RandomAccessFile(file, "rw");     FileChannel fc = fi.getChannel();     return fc.tryLock();   } }