多线程下载

gengen201314

package cn.com.hs.down;import java.io.File;import java.io.InputStream;import java.io.RandomAccessFile;import java.net.HttpURLConnection;import java.net.URL;/** * 多线程下载文件 *  * @author Administrator *  */public class DownFile {public static void main(String[] args) {DownFile test = new DownFile();String path = "http://www.qthdaily.com/news/content/attachement/jpg/site1/20100622/0022687bd36c0d8a4cb206.jpg";int threadnum = 3;try {test.down(path, threadnum);} catch (Exception e) {e.printStackTrace();}}/** * 下载 *  * @throws Exception *  */public void down(String path, int threadnum) throws Exception {URL url = new URL(path);HttpURLConnection conn = (HttpURLConnection) url.openConnection();conn.setConnectTimeout(10 * 1000);conn.setRequestMethod("GET");// 获得网络文件的长度int length = conn.getContentLength();//每个线程负责下载的文件大小int block = (length % threadnum) == 0 ? length / threadnum : length/ threadnum + 1;/** * 创建随进访问文件对象 * r:read w:write d:disk--将读取的数据存储到硬盘中,否则就存入到缓存中 */File file = new File(getFileName(path));RandomAccessFile accessFile = new RandomAccessFile(file, "rwd");accessFile.setLength(length);//设置长度;accessFile.close();if (conn.getResponseCode() == 200) {for (int i = 0; i < threadnum; i++) {// 开启线程下载new DownThread(i, file, block, url).start();}}}public String getFileName(String path){return path.substring(path.lastIndexOf("/")+1);}/** * 下载线程 *  * @author Administrator *  */public class DownThread extends Thread {private int id; // 线程idprivate File file;// 目标文件private int block;// 每个线程下载文件的大小private URL url;public DownThread() {}public DownThread(int id, File file, int block, URL url) {this.id = id;this.file = file;this.block = block;this.url = url;}@Overridepublic void run() {int start = (id * block);// 当前线程开始下载处int end = (id + 1) * block - 1;// 当前线程结束下载处// 建立随机操作文件对象try {RandomAccessFile accessFile = new RandomAccessFile(file, "rwd");accessFile.seek(start);// 设置操作文件的入点HttpURLConnection conn = (HttpURLConnection) url.openConnection();conn.setConnectTimeout(5 * 1000);conn.setRequestMethod("GET");// 指定网络位置从什么位置开始下载,到什么位置结束conn.setRequestProperty("Range", "bytes=" + start + "-" + end+ "");InputStream in = conn.getInputStream();// 获得输入流byte[] data = new byte[1024];int len = 0;while ((len = in.read(data)) != -1) {accessFile.write(data, 0, len);}accessFile.close();in.close();System.out.println("线程:" + id + "下载完成!");} catch (Exception e) {e.printStackTrace();}}}}