Java的多线程下载

原创
2017/07/03 10:00
阅读数 47
import java.io.InputStream;
import java.io.RandomAccessFile;
import java.net.*;


public class DownUtil
{
// 定义下载资源的路径
	private String path;
// 指定所下载的文件的保存位置
	private String targetFile;
// 定义需要使用多少线程下载资源
	private int threadNum;
// 定义下载的线程对象
	private DownThread[] threads;
// 定义下载的文件的总大小
	private int fileSize;


	public DownUtil(String path, String targetFile, int threadNum)
	{
		this.path = path;
		this.threadNum = threadNum;
// 初始化threads数组
		threads = new DownThread[threadNum];
		this.targetFile = targetFile;
	}


	public void download() throws Exception
	{
		URL url = new URL(path);
		HttpURLConnection conn = (HttpURLConnection) url.openConnection();
		conn.setConnectTimeout(5 * 1000);
		conn.setRequestMethod("GET");
		conn.setRequestProperty(
			"Accept",
			"image/gif, image/jpeg, image/pjpeg, image/pjpeg, "
			+ "application/x-shockwave-flash, application/xaml+xml, "
			+ "application/vnd.ms-xpsdocument, application/x-ms-xbap, "
			+ "application/x-ms-application, application/vnd.ms-excel, "
			+ "application/vnd.ms-powerpoint, application/msword, */*");
		conn.setRequestProperty("Accept-Language", "zh-CN");
		conn.setRequestProperty("Charset", "UTF-8");
		conn.setRequestProperty("Connection", "Keep-Alive");
// 得到文件大小
		fileSize = conn.getContentLength();
		System.out.println("fileSize:"+fileSize);
		conn.disconnect();
		int currentPartSize = fileSize / threadNum + 1;
		System.out.println("currentPartSize:"+currentPartSize);
		RandomAccessFile file = new RandomAccessFile(targetFile, "rw");
// 设置本地文件的大小
		file.setLength(fileSize);
		file.close();
		for (int i = 0; i < threadNum; i++)
		{
// 计算每条线程的下载的开始位置
			int startPos = i * currentPartSize;
// 每个线程使用一个RandomAccessFile进行下载
			RandomAccessFile currentPart = new RandomAccessFile(targetFile,
				"rw");
// 定位该线程的下载位置
			currentPart.seek(startPos);
// 创建下载线程
			threads[i] = new DownThread(startPos, currentPartSize,
				currentPart);
// 启动下载线程
			threads[i].start();
		}
	}


// 获取下载的完成百分比
	public double getCompleteRate()
	{
// 统计多条线程已经下载的总大小
		int sumSize = 0;
		for (int i = 0; i < threadNum; i++)
		{
			sumSize += threads[i].length;
		}
// 返回已经完成的百分比
		return sumSize * 1.0 / fileSize;
	}


	private class DownThread extends Thread
	{
// 当前线程的下载位置
		private int startPos;
// 定义当前线程负责下载的文件大小
		private int currentPartSize;
// 当前线程需要下载的文件块
		private RandomAccessFile currentPart;
// 定义已经该线程已下载的字节数
		public int length;


		public DownThread(int startPos, int currentPartSize,
			RandomAccessFile currentPart)
		{
			this.startPos = startPos;
			this.currentPartSize = currentPartSize;
			this.currentPart = currentPart;
		}


		@Override
		public void run()
		{
			try
			{
				URL url = new URL(path);
				HttpURLConnection conn = (HttpURLConnection)url
				.openConnection();
				conn.setConnectTimeout(5 * 1000);
				conn.setRequestMethod("GET");
				conn.setRequestProperty(
					"Accept",
					"image/gif, image/jpeg, image/pjpeg, image/pjpeg, "
					+ "application/x-shockwave-flash, application/xaml+xml, "
					+ "application/vnd.ms-xpsdocument, application/x-ms-xbap, "
					+ "application/x-ms-application, application/vnd.ms-excel, "
					+ "application/vnd.ms-powerpoint, application/msword, */*");
				conn.setRequestProperty("Accept-Language", "zh-CN");
				conn.setRequestProperty("Charset", "UTF-8");
				InputStream inStream = conn.getInputStream();
// 跳过startPos个字节,表明该线程只下载自己负责哪部分文件。
				inStream.skip(this.startPos);
				byte[] buffer = new byte[1024];
				int hasRead = 0;
// 读取网络数据,并写入本地文件
				while (length < currentPartSize
					&& (hasRead = inStream.read(buffer)) != -1)
				{
					currentPart.write(buffer, 0, hasRead);
// 累计该线程下载的总大小
					length += hasRead;
				}
				currentPart.close();
				inStream.close();
			}
			catch (Exception e)
			{
				e.printStackTrace();
			}
		}
	}
}



public class MultiThreadDown
{
	public static void main(String[] args) throws Exception
	{
// 初始化DownUtil对象
		final DownUtil downUtil = new DownUtil("http://www.crazyit.org/"
			+ "attachments/month_1403/1403202355ff6cc9a4fbf6f14a.png"
			, "iOS.png", 4);
// 开始下载
		downUtil.download();
		new Thread(() -> {
			while(downUtil.getCompleteRate() < 1)
			{
// 每隔0.1秒查询一次任务的完成进度,
// GUI程序中可根据该进度来绘制进度条
				System.out.println("已完成:"
					+ downUtil.getCompleteRate());
				try
				{
					Thread.sleep(100);
				}
				catch (Exception ex){}
			}
		}).start();
	}
}

 

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