多线程断点续传

wuhongyu

    以前看过一个前辈写的断点续传的文章，记得当时没看懂，就扔那了。昨天翻了出来，自己也仿照写了一个，不过感觉没人家写的好，有点乱，希望大家能来批评、指正，给点意见！
 
    功能很简单，就是启动多个线程分别从给定的地址下载数据，用RandomAccessFile写到目标文件。实现思路是：
    1、获得连接的长度（即要下载的文件大小），除以设定的线程数，即得到每个线程要下载的大小。
    2、记录临时文件，文件中记录每个线程的编号（id），该线程要下载的起始位置、终止位置和当前位置（当前位置在首次下载时与起始位置相同）。
    3、启动具体执行下载任务的线程，并等待其结束。
    4、下载完成，删除临时文件。
 
代码如下:
主线程及测试的main方法
package com.why.download.test;import java.io.DataOutputStream;import java.io.File;import java.io.FileOutputStream;import java.io.IOException;import java.math.BigDecimal;import java.net.HttpURLConnection;import java.net.URL;import java.net.URLConnection;import java.util.UUID;import java.util.concurrent.CountDownLatch;import java.util.concurrent.ExecutorService;import java.util.concurrent.Executors;/** *  * @author why * */public class DownLoad {//文件目录、文件名public String fileDir = "E:/MyDownLoad";public String fileName;//超时重连时间public long reconnectTime = 5;//线程数private int poolSize = 5;//每个线程的缓冲区大小public int bufferSize = 1024;//url地址private String urlLocation = null;public DownLoad(){}public DownLoad(String url){this.urlLocation = url;}public void downLoad(){if(this.urlLocation == null || "".equals(this.urlLocation))return;downLoad(this.urlLocation);}public void downLoad(String urlLocation){File file = null;File tempFile = null;CountDownLatch latch;URL url = null;ExecutorService pool = Executors.newCachedThreadPool();long contentLength = 0;long threadLength = 0;try {//如果未指定名称，则从url中获得下载的文件格式与名字if(fileName == null || "".equals(fileName)){this.fileName = urlLocation.substring(urlLocation.lastIndexOf("/") + 1,urlLocation.lastIndexOf("?") > 0 ? urlLocation.lastIndexOf("?"): urlLocation.length());if ("".equalsIgnoreCase(this.fileName)) {this.fileName = UUID.randomUUID().toString();}}new File(fileDir).mkdirs();file = new File(fileDir + File.separator + fileName);tempFile = new File(fileDir + File.separator + fileName + "_temp");url = new URL(urlLocation);HttpURLConnection conn = (HttpURLConnection) url.openConnection();setHeader(conn);//得到content的长度contentLength = conn.getContentLength();System.out.println("total length=" + contentLength);//把context分为poolSize段，计算每段的长度。//threadLength = contentLength / this.poolSize;BigDecimal b1 = new BigDecimal(Double.toString(contentLength));BigDecimal b2 = new BigDecimal(Double.toString(this.poolSize));threadLength = b1.divide(b2, 0, BigDecimal.ROUND_HALF_UP).longValue();if(file.exists() && tempFile.exists()){//如果文件已存在，根据临时文件中记载的线程数量，继续上次的任务latch = new CountDownLatch((int)tempFile.length()/28);for(int i=0;i<tempFile.length()/28;i++){pool.submit(new DownLoadTask(file, tempFile, url, i+1,latch,reconnectTime,bufferSize));}}else{//如果下载的目标文件不存在，则创建新文件latch = new CountDownLatch(poolSize);file.createNewFile();tempFile.createNewFile();DataOutputStream os = new DataOutputStream(new FileOutputStream(tempFile));for(int i=0;i<this.poolSize;i++){os.writeInt(i+1);os.writeLong(i*threadLength);if(i==this.poolSize-1){//最后一个线程的结束位置应为文件末端os.writeLong(contentLength);}else{os.writeLong((i+1)*threadLength);}os.writeLong(i*threadLength);pool.submit(new DownLoadTask(file, tempFile, url, i+1,latch,reconnectTime,bufferSize));}os.close();}//等待下载任务完成latch.await();//删除临时文件tempFile.delete();} catch (IOException e) {e.printStackTrace();} catch (InterruptedException e) {e.printStackTrace();} finally{pool.shutdown(); }}private void setHeader(URLConnection conn) {conn.setRequestProperty("User-Agent","Mozilla/5.0 (X11; U; Linux i686; en-US; rv:1.9.0.3) Gecko/2008092510 Ubuntu/8.04 (hardy) Firefox/3.0.3");conn.setRequestProperty("Accept-Language", "en-us,en;q=0.7,zh-cn;q=0.3");conn.setRequestProperty("Accept-Encoding", "aa");conn.setRequestProperty("Accept-Charset","ISO-8859-1,utf-8;q=0.7,*;q=0.7");conn.setRequestProperty("Keep-Alive", "300");conn.setRequestProperty("Connection", "keep-alive");conn.setRequestProperty("If-Modified-Since", "Fri, 02 Jan 2009 17:00:05 GMT");conn.setRequestProperty("If-None-Match", "\"1261d8-4290-df64d224\"");conn.setRequestProperty("Cache-Control", "max-age=0");conn.setRequestProperty("Referer","http://www.skycn.com/soft/14857.html");}public String getFileDir() {return fileDir;}public void setFileDir(String fileDir) {this.fileDir = fileDir;}public String getFileName() {return fileName;}public void setFileName(String fileName) {this.fileName = fileName;}public long getReconnectTime() {return reconnectTime;}public void setReconnectTime(long reconnectTime) {this.reconnectTime = reconnectTime;}public int getPoolSize() {return poolSize;}public void setPoolSize(int poolSize) {this.poolSize = poolSize;}public int getBufferSize() {return bufferSize;}public void setBufferSize(int bufferSize) {this.bufferSize = bufferSize;}/** * @param args */public static void main(String[] args) {DownLoad dl = new DownLoad();dl.setFileDir("E:/MyDownLoad/music/");dl.setFileName("大笑江湖.mp3");dl.setPoolSize(20);long beginTime = System.currentTimeMillis();dl.downLoad("http://mh.163k.com/UploadFile/video/2010/12-13/201012131213448942190.mp3");long endTime = System.currentTimeMillis();BigDecimal b1 = new BigDecimal(endTime - beginTime);BigDecimal b2 = new BigDecimal(1000);double cost = b1.divide(b2, 2, BigDecimal.ROUND_HALF_UP).doubleValue();System.out.println("Time cost:" + cost + "s");}}  
执行下载任务的线程：
package com.why.download.test;import java.io.File;import java.io.FileNotFoundException;import java.io.IOException;import java.io.InputStream;import java.io.RandomAccessFile;import java.net.HttpURLConnection;import java.net.URL;import java.net.URLConnection;import java.util.concurrent.Callable;import java.util.concurrent.CountDownLatch;import java.util.concurrent.TimeUnit;/** *  * @author why * */public class DownLoadTask implements Callable<String>{//超时重连时间private long reconnectTime = 5;//缓冲区大小private int bufferSize = 1024;private CountDownLatch latch;private RandomAccessFile file = null;private RandomAccessFile tempFile = null;private URL url = null;private int id;private long startPosition;private long endPosition;private long currentPosition ;public DownLoadTask(File file,File tempFile,URL url,int id,CountDownLatch latch,long reconnectTime,int bufferSize){try {this.file = new RandomAccessFile(file, "rw");this.tempFile = new RandomAccessFile(tempFile, "rw");} catch (FileNotFoundException e) {e.printStackTrace();}this.url = url;this.id = id;this.latch = latch;}public String call(){try {tempFile.seek((id-1)*28);tempFile.readInt();this.startPosition = tempFile.readLong();this.endPosition = tempFile.readLong();this.currentPosition = tempFile.readLong();} catch (IOException e) {e.printStackTrace();}System.out.println("Thread " + id + " begin!");HttpURLConnection conn = null;InputStream inputStream = null;while(true){try {tempFile.seek(id*28 - 8);// 打开URLConnectionconn = (HttpURLConnection) this.url.openConnection();setHeader(conn);// 设置连接超时时间为10000msconn.setConnectTimeout(10000);// 设置读取数据超时时间为10000msconn.setReadTimeout(10000);if (currentPosition < endPosition) {// 设置下载数据的起止区间conn.setRequestProperty("Range", "bytes=" + currentPosition + "-" + endPosition);System.out.println("Thread " + id + " startPosition=" + startPosition + ",endPosition=" + endPosition + ",currentPosition=" + currentPosition);file.seek(currentPosition);// 判断http status是否为HTTP/1.1 206 Partial Content或者200 OK// 如果不是以上两种状态，把status改为STATUS_HTTPSTATUS_ERRORif (conn.getResponseCode() != HttpURLConnection.HTTP_OK&& conn.getResponseCode() != HttpURLConnection.HTTP_PARTIAL) {System.out.println("Thread " + id + ": code = " + conn.getResponseCode() + ", status = " + conn.getResponseMessage());file.close();conn.disconnect();System.out.println("Thread " + id + " finished.");break;}inputStream = conn.getInputStream();int len = 0;byte[] b = new byte[bufferSize];while ((len = inputStream.read(b)) != -1) {file.write(b, 0, len);currentPosition += len;// set tempFile now positiontempFile.seek(id*28 - 8);tempFile.writeLong(currentPosition);}file.close();tempFile.close();inputStream.close();conn.disconnect();}System.out.println("Thread " + id + " finished.");break;} catch (IOException e) {try {TimeUnit.SECONDS.sleep(getReconnectTime());} catch (InterruptedException e1) {e1.printStackTrace();}continue;}}latch.countDown();return "finish";}private void setHeader(URLConnection conn) {conn.setRequestProperty("User-Agent","Mozilla/5.0 (X11; U; Linux i686; en-US; rv:1.9.0.3) Gecko/2008092510 Ubuntu/8.04 (hardy) Firefox/3.0.3");conn.setRequestProperty("Accept-Language", "en-us,en;q=0.7,zh-cn;q=0.3");conn.setRequestProperty("Accept-Encoding", "aa");conn.setRequestProperty("Accept-Charset","ISO-8859-1,utf-8;q=0.7,*;q=0.7");conn.setRequestProperty("Keep-Alive", "300");conn.setRequestProperty("Connection", "keep-alive");conn.setRequestProperty("If-Modified-Since", "Fri, 02 Jan 2009 17:00:05 GMT");conn.setRequestProperty("If-None-Match", "\"1261d8-4290-df64d224\"");conn.setRequestProperty("Cache-Control", "max-age=0");conn.setRequestProperty("Referer","http://www.skycn.com/soft/14857.html");}public long getReconnectTime() {return reconnectTime;}public void setReconnectTime(long reconnectTime) {this.reconnectTime = reconnectTime;}public int getBufferSize() {return bufferSize;}public void setBufferSize(int bufferSize) {this.bufferSize = bufferSize;}}     最近一直在测试，写文档，好久没敲代码了。手有点痒，写着玩的，代码写的不是很工整，纯属娱乐！