字节流加缓冲流

前面介绍了基本的字节流和字符流,那只是基本,如果要处理一个很大的文件,那就要在节点流前加入BufferedOutputStream 和BufferedInputStream 这两个处理流,这样能大大提高我们的效率.

package com.buffer;

import java.io.BufferedInputStream;
import java.io.BufferedOutputStream;
import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.IOException;
import java.nio.ByteBuffer;
import java.nio.channels.Channel;
import java.nio.channels.ReadableByteChannel;

/**
 * 
 * @author Yijun
 *         这次我们来看下buffer的作用,用了readByChannel,readNotbuffer,readBuffer三种方法比较buffer读的优异性
 *         用writeBuffer,writeNoBuffer比较buffer写的优异性
 */
public class TestBufferFile {

	/**
	 * @param args
	 * @throws IOException
	 */
	public static void main(String[] args) throws IOException {
		// TODO Auto-generated method stub

		String src = "F:\\java_test\\a.jpg";// 原文件
		String src2 = "F:\\java_test\\copy\\a.jpg";// 目标文件1
		String src3 = "F:\\java_test\\copy\\aCopy.jpg";// 目标文件2
		long st = System.currentTimeMillis();// 获得现在时间点

		readByChannel(src);// ReadableByteChannel 方法
		System.out.println("channel :  " + (System.currentTimeMillis() - st));
		st = System.currentTimeMillis();
		readNotbuffer(src);// 不用buffer读取文件
		System.out.println("buffered :  " + (System.currentTimeMillis() - st));
		st = System.currentTimeMillis();
		readBuffer(src);// 使用buffer读取文件
		System.out.println("not buffered :  "
				+ (System.currentTimeMillis() - st));
		/***************************************************************/
		st = System.currentTimeMillis();
		writeBuffer(src2, src);// 使用buffer写文件
		System.out.println("writeBuffer :  "
				+ (System.currentTimeMillis() - st));
		/*********************************************************************/
		st = System.currentTimeMillis();
		writeNoBuffer(src3, src);// 不使用buffer写文件
		System.out.println("writeNoBuffer :  "
				+ (System.currentTimeMillis() - st));
	}

	private static void writeNoBuffer(String src2, String src)
			throws IOException {
		FileInputStream fin = new FileInputStream(src);
		FileOutputStream fout = new FileOutputStream(src2);
		byte[] array = new byte[1024];
		int len = 0;
		while ((len = fin.read(array)) > 0) {
			fout.write(array, 0, len);
		}
	}

	private static void writeBuffer(String src2, String src) throws IOException {
		FileOutputStream fout = new FileOutputStream(src2);
		BufferedOutputStream bout = new BufferedOutputStream(fout);
		FileInputStream fin = new FileInputStream(src);
		BufferedInputStream bin = new BufferedInputStream(fin);
		byte[] data = new byte[1024];
		while (bin.read(data) != -1) {
			bout.write(data);
		}
		bout.flush();// //将缓冲区中的数据全部写出
	}

	public static void readNotbuffer(String src) throws IOException {

		FileInputStream fin = new FileInputStream(src);
		byte[] buffer = new byte[1024];
		int len = 0;
		while ((len = fin.read(buffer)) > 0) {

		}
		fin.close();

	}

	public static void readBuffer(String src) throws IOException {

		FileInputStream fin = new FileInputStream(src);
		BufferedInputStream bufferin = new BufferedInputStream(fin, 1024);
		byte[] buffer = new byte[1024];
		int len = 0;
		while ((len = bufferin.read(buffer)) > 0) {

		}
		bufferin.close();
		fin.close();
	}

	public static void readByChannel(String src) throws IOException {
		FileInputStream fin = new FileInputStream(src);

		ReadableByteChannel channel = fin.getChannel();
		ByteBuffer buffer = ByteBuffer.allocate(1024);// 创建一个指定1024的ByteBuffer
		while (channel.read(buffer) > 0) {
			buffer.flip();// 读写状态切换
			buffer.clear();// 清空
		}
		fin.close();
	}

}

我们运行代码后就能发现,使用buffer的好处,提高了我们处理的时间..