把文件abc.txt复制一份名为demo.txt的文件 

package cn.zzx.file;

import java.io.*;

public class BufferedDemo {

	public static void main(String[] args) throws Exception {
		File f1 = new File("D:/demo.txt");    // 写入数据
		File f2 = new File("D:/abc.txt");     //读取数据
		InputStream read = new FileInputStream(f2);   
		OutputStream write = new FileOutputStream(f1);
		//放到缓存区
		BufferedInputStream br = new BufferedInputStream(read);
		BufferedOutputStream bw = new BufferedOutputStream(write);
		byte [] b = new byte[1024];
		int len = 0;
		//循环读取，读完返回负1
		while((len=br.read(b))!=-1){
			//边读边写
			bw.write(b, 0,len);
			
		}
		bw.flush();//强制刷新缓冲区
		bw.close(); //关闭写出流
		br.close();//关闭读入流
		

	}

}