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package com.test.download;import java.io.File;import java.io.InputStream;import java.io.RandomAccessFile;import java.net.HttpURLConnection;import java.net.URL;/* * 多线程下载 */public class MulThreadDownload { public static void main(String[] args) throws Exception { String path = "http://pic.4j4j.cn/upload/pic/20130909/681ebf9d64.jpg"; new MulThreadDownload().download(path,3); } public void download (String path,int threadsize) throws Exception{ URL url = new URL(path); HttpURLConnection conn = (HttpURLConnection) url.openConnection(); conn.setConnectTimeout(5000); conn.setRequestMethod("GET"); if(conn.getResponseCode() == 200){ //获取网络文件长度 int length = conn.getContentLength(); //新建本地文件保存下载数据 File file = new File(getFilename(path)); //计算每条线程负责下载的数据量 int block = length%threadsize==0 ? length/threadsize : length/threadsize+1; //开启指定数目的线程同时下载 for(int threadid = 0; threadid < threadsize; threadid++){ new DownloadThread(threadid,block,url,file).start(); } }else{ System.out.println("下载失败！"); } } private class DownloadThread extends Thread{ private int threadid; //线程编号 private int block; //下载块大小 private URL url; //下载链接 private File file; //下载数据保存文件 public DownloadThread(int threadid, int block, URL url, File file) { this.threadid = threadid; this.block = block; this.url = url; this.file = file; } public void run() { int start = threadid * block; //本线程下载数据写入文件开始位置 int end = (threadid+1) * block - 1; //本线程下载数据写入文件结束位置 try { //创建一个随机访问文件流对象 RandomAccessFile accessFile = new RandomAccessFile(file, "rwd"); //文件指针偏移至正确写入位置 accessFile.seek(start); HttpURLConnection conn = (HttpURLConnection) url.openConnection(); conn.setConnectTimeout(5000); conn.setRequestMethod("GET"); //设置请求数据的范围 conn.setRequestProperty("Range", "bytes="+start+"-"+end); if(conn.getResponseCode() == 206){//状态码206:（部分内容） 服务器成功处理了部分 GET 请求 InputStream inStream = conn.getInputStream(); byte[] buffer = new byte[1024]; int len = 0; while((len = inStream.read(buffer)) != -1){ accessFile.write(buffer, 0, len); } accessFile.close(); inStream.close(); } System.out.println("第"+(threadid+1)+"部分下载完成"); } catch (Exception e) { e.printStackTrace(); } } } private String getFilename(String path) { return path.substring(path.lastIndexOf("/")+1); }}标签：
原文地址：http://www.cnblogs.com/sandea/p/4612319.html
