filechanneltest.java

精通java核心技术》随书源代码

// ==================== Program Discription =====================
// 程序名称：示例2-2 : FileChannelTest.java
// 程序目的：学习java nio#FileChannel
// ==============================================================

import java.nio.ByteBuffer;
import java.nio.channels.FileChannel;
import java.io.File;
import java.io.RandomAccessFile;
import java.io.IOException;


public class FileChannelTest
{
	public static void main (String [] argv)
		throws IOException
	{
		//创建一个临时的文件
		File temp = File.createTempFile ("temp", null);
		RandomAccessFile file = new RandomAccessFile (temp, "rw");
		FileChannel channel = file.getChannel();
		// 创建一个Buffer
		ByteBuffer byteBuffer = ByteBuffer.allocateDirect (100);

		insertData (0, byteBuffer, channel);
		insertData (60, byteBuffer, channel);
		insertData (600, byteBuffer, channel);

		System.out.println ("Wrote temp file '" + temp.getPath()+ "', size=" + channel.size());
		System.out.println(channel.position());
		file.seek(100);
		System.out.println("after file.seek(100),position="+channel.position());	
		
		getData(0,byteBuffer,channel);
		channel.close();
		file.close();
	}
	
	private static void getData(int position,ByteBuffer buffer,FileChannel channel)throws IOException
	{
		String temp="";
		buffer.clear();
		channel.position(position);
		channel.read(buffer,60);
	    buffer.flip();
		System.out.println(buffer.asCharBuffer().toString().getBytes ("US-ASCII"));
		//System.out.println(buffer);
	}		

	private static void insertData (int position, ByteBuffer buffer,
		FileChannel channel)
		throws IOException
	{
		String string = "#<- position" + position;

		buffer.clear();
		buffer.put (string.getBytes ("US-ASCII"));
		buffer.flip();

		channel.position (position);
		channel.write (buffer);
	}
}