mutildown.java

疯狂Java讲义_源码(含Java设计模式CHM

import java.io.*;
import java.net.*;
/**
 * Description:
 * <br/>Copyright (C), 2008-2010, Yeeku.H.Lee
 * <br/>This program is protected by copyright laws.
 * <br/>Program Name:
 * <br/>Date:
 * @author  Yeeku.H.Lee [e-mail]
 * @version  1.0
 */
//定义下载从start到end的内容的线程
class DownThread extends Thread
{
	//定义字节数组（取水的竹筒）的长度
	private final int BUFF_LEN = 32;
	//定义下载的起始点
	private long start;
	//定义下载的结束点
	private long end;
	//下载资源对应的输入流
	private InputStream is;
	//将下载到的字节输出到raf中
	private RandomAccessFile raf ;

	//构造器，传入输入流，输出流和下载起始点、结束点
	public DownThread(long start , long end 
		, InputStream is , RandomAccessFile raf)
	{
		//输出该线程负责下载的字节位置
		System.out.println(start + "---->"  + end);
		this.start = start;
		this.end = end;
		this.is = is;
		this.raf = raf;
	}
	public void run()
	{
		try
		{
			is.skip(start);
			raf.seek(start); 
			//定义读取输入流内容的的缓存数组（竹筒）
			byte[] buff = new byte[BUFF_LEN];
			//本线程负责下载资源的大小
			long contentLen = end - start;
			//定义最多需要读取几次就可以完成本线程的下载
			long times = contentLen / BUFF_LEN + 4;
			//实际读取的字节数
			int hasRead = 0;
			for (int i = 0; i < times ; i++)
			{
				hasRead = is.read(buff);
				//如果读取的字节数小于0，则退出循环！
				if (hasRead < 0)
				{
					break;
				}
				raf.write(buff , 0 , hasRead);
			}			
		}
		catch (Exception ex)
		{
			ex.printStackTrace();
		}
		//使用finally块来关闭当前线程的输入流、输出流
		finally
		{
			try
			{
				if (is != null)
				{
					is.close();
				}
				if (raf != null)
				{
					raf.close();
				}
			}
			catch (Exception ex)
			{
				ex.printStackTrace();
			}
		}
	}
}
public class MutilDown
{
	public static void main(String[] args)
	{
		final int DOWN_THREAD_NUM = 4;
		final String OUT_FILE_NAME = "down.jpg";
		InputStream[] isArr = new InputStream[DOWN_THREAD_NUM];
		RandomAccessFile[] outArr = new RandomAccessFile[DOWN_THREAD_NUM];
		try
		{
			//创建一个URL对象
			URL url = new URL("http://images.china-pub.com/"
				+ "ebook35001-40000/35850/shupi.jpg");
			//以此URL对象打开第一个输入流
			isArr[0] = url.openStream();
			long fileLen = getFileLength(url);
			System.out.println("网络资源的大小" + fileLen);
			//以输出文件名创建第一个RandomAccessFile输出流
			outArr[0] = new RandomAccessFile(OUT_FILE_NAME , "rw");
			//创建一个与下载资源相同大小的空文件
			for (int i = 0 ; i < fileLen ; i++ )
			{
				outArr[0].write(0);
			}
			//每线程应该下载的字节数
			long numPerThred = fileLen / DOWN_THREAD_NUM;
			//整个下载资源整除后剩下的余数
			long left = fileLen % DOWN_THREAD_NUM;
			for (int i = 0 ; i < DOWN_THREAD_NUM; i++)
			{
				//为每个线程打开一个输入流、一个RandomAccessFile对象，
				//让每个线程分别负责下载资源的不同部分。
				if (i != 0)
				{
					//以URL打开多个输入流
					isArr[i] = url.openStream();
					//以指定输出文件创建多个RandomAccessFile对象
					outArr[i] = new RandomAccessFile(OUT_FILE_NAME , "rw");
				}
				//分别启动多个线程来下载网络资源
				if (i == DOWN_THREAD_NUM - 1 )
				{
					//最后一个线程下载指定numPerThred+left个字节
					new DownThread(i * numPerThred , (i + 1) * numPerThred + left
						, isArr[i] , outArr[i]).start();
				}
				else
				{
					//每个线程负责下载一定的numPerThred个字节
					new DownThread(i * numPerThred , (i + 1) * numPerThred
						, isArr[i] , outArr[i]).start();
				}
			}
		}
		catch (Exception ex)
		{
			ex.printStackTrace();
		}
	}
	//定义获取指定网络资源的长度的方法
	public static long getFileLength(URL url) throws Exception
	{
		long length = 0;
		//打开该URL对应的URLConnection。
		URLConnection con = url.openConnection();
		//获取连接URL资源的长度
		long size = con.getContentLength();
		length = size;
		return length;
	}
}