Java FileChannel tryLock实例讲解

// Java Program to illustarte FileChannel Class 
// tryLock() method 
  
// Importing libraries 
import java.io.IOException; 
import java.nio.ByteBuffer; 
import java.nio.channels.FileChannel; 
import java.nio.channels.FileLock; 
import java.nio.file.Path; 
import java.nio.file.Paths; 
import java.nio.file.StandardOpenOption; 
  
// save the file named as GFG.java 
public class GFG extends Thread { 
    
    // content to be written in the file. 
    String input 
        = "geeks for geeks is a learning portal for computer sciences."; 
    
    ByteBuffer buf = ByteBuffer.wrap(input.getBytes()); 
    
    // path of the file 
    String fp = "gfg.txt"; 
    
      // file channel class object 
    Path pt = Paths.get(fp); 
  
    public void run() 
    { 
        try { 
            
            // the thread says if file is opened. 
            FileChannel fc = FileChannel.open( 
                pt, StandardOpenOption.WRITE, 
                StandardOpenOption.APPEND); 
            System.out.println( 
                Thread.currentThread().getId() 
                + "says:File channel is opened for writing"); 
            
            // trying lock 
            fc.tryLock(0L, Long.MAX_VALUE, false); 
            System.out.println( 
                Thread.currentThread().getId() 
                + "says:acquiring lock"); 
  
            // writing 
            fc.write(buf); 
            // release the Lock after writing 
            System.out.print(Thread.currentThread().getId() 
                             + "says:"); 
            System.out.println( 
                "writing is done, closing the file"); 
  
            // Closing the file connections 
            fc.close(); 
        } 
  
        // Catch block to handle the exception 
        catch (Exception e) { 
            // Getting and printing current threads 
            System.out.println( 
                Thread.currentThread().getId() 
                + "says:Exception" + e); 
        } 
  
        // Here, one file raises exception since the file 
        // is being written by another thread. 
    } 
  
    // Main driver method 
    public static void main(String[] args) throws Exception 
    { 
  
        // Creating an object in the main() method 
        GFG g1 = new GFG(); 
        GFG g2 = new GFG(); 
  
        // Calling start() methods over the objects 
        g1.start(); 
        g2.start(); 
  
        // Here Two thread in concurrency 
        // are trying to access the file 
    } 
}