package com.java7developer.chapter2;
import java.nio.*;
import java.nio.channels.*;
import java.nio.file.*;
import java.io.IOException;
public class Nio2ReadLargeLogFile implements
CompletionHandler<Integer, AsynchronousFileChannel> {
// need to keep track of the next position.
int pos = 0;
AsynchronousFileChannel channel = null;
ByteBuffer buffer = null;
public void completed(Integer result, AsynchronousFileChannel attachment) {
// System.out.println("bytes num " + result);
// if result is -1 means nothing was read.
if (result != -1) {
pos += result; // don't read the same text again.
// your output command.
//这里必须读取0,result直接的buffer，否则会读取到垃圾数据
System.out.print(new String(buffer.array(),0,result));
// buffer.clear(); // reset the buffer so you can read more.
buffer.flip();
attachment.read(buffer, pos, attachment, this);
} else {
return;
}
// initiate another asynchronous read, with this.
}
public void failed(Throwable exc, AsynchronousFileChannel attachment) {
System.err.println("Error!");
exc.printStackTrace();
}
public void doit() {
Path file = Paths.get("c:/a");
AsynchronousFileChannel channel = null;
try {
channel = AsynchronousFileChannel.open(file);
} catch (IOException e) {
System.err.println("Could not open file: " + file.toString());
System.exit(1); // yeah. heh.
}
buffer = ByteBuffer.allocate(1000);
// start off the asynch read.
channel.read(buffer, pos, channel, this);
// this method now exits, thread returns to main and waits for user
// input.
}
public static void main(String[] args) {
Nio2ReadLargeLogFile tn = new Nio2ReadLargeLogFile();
tn.doit();
// 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) {
}
}
}
