AsynchronousFileChannel读文件

import java.nio.*; 
import java.nio.channels.*; 
import java.nio.file.*; 
import java.io.IOException; 

public class TryNio implements CompletionHandler<Integer, AsynchronousFileChannel> { 
     // need to keep track of the next position. 
     int position = 0; 
     AsynchronousFileChannel channel = null; 
     ByteBuffer buffer = null; 

     public void completed(Integer result, AsynchronousFileChannel attachment) { 
       // if result is -1 means nothing was read. 
       if (result != -1) { 
         position += result; // don't read the same text again. 
             // your output command. 
         System.out.println(new String(buffer.array(), 0, result)); 

         buffer.clear(); // reset the buffer so you can read more. 
       } 
         // initiate another asynchronous read, with this. 
       attachment.read(buffer, position, attachment, this); 
     } 
     
     public void failed(Throwable exc, AsynchronousFileChannel attachment) { 
       System.err.println ("Error!"); 
       exc.printStackTrace(); 
     } 

     public void doIt(String inFileName) { 
       Path file = Paths.get(inFileName); 
       try {
         channel = AsynchronousFileChannel.open(file); 
       } catch (IOException e) { 
         System.err.println ("Could not open file: " + file+ e); 
         System.exit(1); // yeah. heh. 
       } 
       buffer = ByteBuffer.allocate(1000); 

       // start off the asynch read. 
       channel.read(buffer, position, channel, this); 
       // this method now exits, thread returns to main and waits for user input. 
     } 

     public static void main (String [] args) { 
       TryNio tn = new TryNio(); 
	   String inFileName = "/var/log/syslog";
       tn.doIt(inFileName); 
      // wait fur user to press a key otherwise java exits because the 
      // asynch thread isn't important enough to keep it running. 
       try { System.in.read(); } catch (IOException e) { } 
     } 
}