我的Java开发学习之旅------>Java多线程下载文件 实例

import java.io.File;
import java.io.InputStream;
import java.io.RandomAccessFile;
import java.net.HttpURLConnection;
import java.net.URL;

public class MulThreadDownload {
	public static void main(String[] args) throws Exception {
		String path = "http://192.168.1.100:8080/Hello/Big.exe";
		new MulThreadDownload().download(path, 3);
	}

	/**
	 * 下载文件
	 *
	 * @param path
	 *            网络文件路径
	 * @param threadSize
	 *            线程数
	 * @throws Exception
	 */
	private void download(String path, int threadSize) throws Exception {
		URL url = new URL(path);
		HttpURLConnection connection = (HttpURLConnection) url.openConnection();
		connection.setRequestMethod("GET");
		connection.setConnectTimeout(5000);
		if (connection.getResponseCode() == 200) {
			int length = connection.getContentLength();// 获取网络文件长度
			File file = new File(getFileName(path));
			// 在本地生成一个长度与网络文件相同的文件
			RandomAccessFile accessFile = new RandomAccessFile(file, "rwd");
			accessFile.setLength(length);
			accessFile.close();

			// 计算每条线程负责下载的数据量
			int block = length % threadSize == 0 ? length / threadSize : length
					/ threadSize + 1;
			for (int threadId = 0; threadId < threadSize; threadId++) {
				new DownloadThread(threadId, block, url, file).start();
			}
		} else {
			System.out.println("download fail");
		}
	}

	private class DownloadThread extends Thread {

		private int threadId;
		private int block;
		private URL url;
		private File file;

		public DownloadThread(int threadId, int block, URL url, File file) {
			this.threadId = threadId;
			this.block = block;
			this.url = url;
			this.file = file;
		}

		@Override
		public void run() {
			int start = threadId * block; // 计算该线程从网络文件什么位置开始下载
			int end = (threadId + 1) * block - 1; // 计算下载到网络文件什么位置结束
			try {
				RandomAccessFile accessFile = new RandomAccessFile(file, "rwd");
				accessFile.seek(start);  //从start开始

				HttpURLConnection connection = (HttpURLConnection) url
						.openConnection();
				connection.setRequestMethod("GET");
				connection.setConnectTimeout(5000);
				//设置获取资源数据的范围，从start到end
				connection.setRequestProperty("Range", "bytes=" + start + "-"
						+ end);
				//注意多线程下载状态码是 206  不是200
				if (connection.getResponseCode() == 206) {
					InputStream inputStream = connection.getInputStream();
					byte[] buffer = new byte[1024];
					int len = 0;
					while ((len = inputStream.read(buffer)) != -1) {
						accessFile.write(buffer, 0, len);
					}
					accessFile.close();
					inputStream.close();
				}
				System.out.println("第" + (threadId + 1) + "条线程已经下载完成");
			} catch (Exception e) {
				e.printStackTrace();
			}
		}
	}

	/**
	 * 获取文件名称
	 *
	 * @param path
	 *            网络文件路径
	 * @return
	 */
	private String getFileName(String path) {
		return path.substring(path.lastIndexOf("/") + 1);
	}
}

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  作者：欧阳鹏  欢迎转载，与人分享是进步的源泉！

  转载请保留原文地址：http://blog.csdn.net/ouyang_peng

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