实现网络下载文件功能

public class DownloadStartup {private static final String encoding = "utf-8";public static void main(String[] args) {DownloadTask downloadManager = new DownloadTask();//String urlStr = "http://yztele4.skycn.com/down/Thunder5.9.3.951.zip";String urlStr = "http://apache.freelamp.com/velocity/tools/1.4/velocity-tools-1.4.zip";//String urlStr = "http://www.dianping.com/";downloadManager.setSleepSeconds(5);String downladFileName = downloadManager.download(urlStr, encoding);System.out.println("Download file is " + downladFileName + ".");}}

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public class DownloadTask {// private static transient// 分段下载的线程个数private int threadNum = 5;private URL url = null;private long threadLength = 0;// 目标文件路径与名字public String fileDir = "E:/test/";public String fileName = "test.html";public boolean statusError = false;private String charset;public long sleepSeconds = 5;public String download(String urlStr, String charset) {statusError = false;this.charset = charset;long contentLength = 0;CountDownLatch latch = new CountDownLatch(threadNum);ChildThread[] childThreads = new ChildThread[threadNum];long[] startPos = new long[threadNum];long endPos = 0;try {// 从url中获得下载的文件格式与名字this.fileName = urlStr.substring(urlStr.lastIndexOf("/") + 1, urlStr.lastIndexOf("?")>0 ? urlStr.lastIndexOf("?") : urlStr.length());if("".equalsIgnoreCase(this.fileName)){this.fileName = UUID.randomUUID().toString();}this.url = new URL(urlStr);HttpURLConnection con = (HttpURLConnection) url.openConnection();setHeader(con);// 得到content的长度contentLength = con.getContentLength();// 把context分为threadNum段的话，每段的长度。this.threadLength = contentLength / threadNum;// 第一步，分析已下载的临时文件，设置断点，如果是新的下载任务，则建立目标文件。startPos = setThreadBreakpoint(fileDir, fileName, contentLength,startPos);// 第二步，分多个线程下载文件ExecutorService exec = Executors.newCachedThreadPool();for (int i = 0; i < threadNum; i++) {// 创建子线程来负责下载数据，每段数据的起始位置为(threadLength * i + 已下载长度)startPos[i] += threadLength * i;/* * 设置子线程的终止位置，非最后一个线程即为(threadLength * (i + 1) - 1) * 最后一个线程的终止位置即为下载内容的长度 */if (i == threadNum - 1) {endPos = contentLength;} else {endPos = threadLength * (i + 1) - 1;}// 开启子线程，并执行。ChildThread thread = new ChildThread(this, latch, i,startPos[i], endPos);childThreads[i] = thread;exec.execute(thread);}try {// 等待CountdownLatch信号为0，表示所有子线程都结束。latch.await();exec.shutdown();// 第三步，把分段下载下来的临时文件中的内容写入目标文件中。tempFileToTargetFile(childThreads);} catch (InterruptedException e) {e.printStackTrace();}} catch (IOException e) {e.printStackTrace();}return fileDir + fileName;}private void tempFileToTargetFile(ChildThread[] childThreads) {try {BufferedOutputStream outputStream = new BufferedOutputStream(new FileOutputStream(fileDir + fileName));// 遍历所有子线程创建的临时文件，按顺序把下载内容写入目标文件中for (int i = 0; i < threadNum; i++) {if (statusError) {for (int k = 0; k < threadNum; k++) {if (childThreads[k].tempFile.length() == 0)childThreads[k].tempFile.delete();}System.out.println("本次下载任务不成功，请重新设置线程数。");break;}BufferedInputStream inputStream = new BufferedInputStream(new FileInputStream(childThreads[i].tempFile));System.out.println("Now is file " + childThreads[i].id);int len = 0;long count = 0;byte[] b = new byte[1024];while ((len = inputStream.read(b)) != -1) {count += len;outputStream.write(b, 0, len);if ((count % 4096) == 0) {outputStream.flush();}}inputStream.close();// 删除临时文件if (childThreads[i].status == ChildThread.STATUS_HAS_FINISHED) {childThreads[i].tempFile.delete();}}outputStream.flush();outputStream.close();} catch (FileNotFoundException e) {e.printStackTrace();} catch (IOException e) {e.printStackTrace();}}private long[] setThreadBreakpoint(String fileDir2, String fileName2,long contentLength, long[] startPos) {File file = new File(fileDir + fileName);long localFileSize = file.length();if (file.exists()) {System.out.println("file " + fileName + " has exists!");// 下载的目标文件已存在，判断目标文件是否完整if (localFileSize < contentLength) {System.out.println("Now download continue ... ");// 遍历目标文件的所有临时文件，设置断点的位置，即每个临时文件的长度File tempFileDir = new File(fileDir);File[] files = tempFileDir.listFiles();for (int k = 0; k < files.length; k++) {String tempFileName = files[k].getName();// 临时文件的命名方式为：目标文件名+"_"+编号if (tempFileName != null && files[k].length() > 0&& tempFileName.startsWith(fileName + "_")) {int fileLongNum = Integer.parseInt(tempFileName.substring(tempFileName.lastIndexOf("_") + 1,tempFileName.lastIndexOf("_") + 2));// 为每个线程设置已下载的位置startPos[fileLongNum] = files[k].length();}}}} else {// 如果下载的目标文件不存在，则创建新文件try {file.createNewFile();} catch (IOException e) {e.printStackTrace();}}return startPos;}/** *  * @author annegu * @since 2009-07-16 *  */public class ChildThread extends Thread {public static final int STATUS_HASNOT_FINISHED = 0;public static final int STATUS_HAS_FINISHED = 1;public static final int STATUS_HTTPSTATUS_ERROR = 2;private DownloadTask task;private int id;private long startPosition;private long endPosition;private final CountDownLatch latch;// private RandomAccessFile tempFile = null;private File tempFile = null;//线程状态码private int status = ChildThread.STATUS_HASNOT_FINISHED;public ChildThread(DownloadTask task, CountDownLatch latch, int id,long startPos, long endPos) {super();this.task = task;this.id = id;this.startPosition = startPos;this.endPosition = endPos;this.latch = latch;try {tempFile = new File(this.task.fileDir + this.task.fileName+ "_" + id);if (!tempFile.exists()) {tempFile.createNewFile();}} catch (IOException e) {e.printStackTrace();}}public void run() {System.out.println("Thread " + id + " run ...");HttpURLConnection con = null;InputStream inputStream = null;BufferedOutputStream outputStream = null;long count = 0;long threadDownloadLength = endPosition - startPosition;try {outputStream = new BufferedOutputStream(new FileOutputStream(tempFile.getPath(), true));} catch (FileNotFoundException e2) {e2.printStackTrace();}for (;;) {try {// 打开URLConnectioncon = (HttpURLConnection) task.url.openConnection();setHeader(con);con.setAllowUserInteraction(true);// 设置连接超时时间为10000mscon.setConnectTimeout(10000);// 设置读取数据超时时间为10000mscon.setReadTimeout(10000);if (startPosition < endPosition) {// 设置下载数据的起止区间con.setRequestProperty("Range", "bytes="+ startPosition + "-" + endPosition);System.out.println("Thread " + id+ " startPosition is " + startPosition);System.out.println("Thread " + id + " endPosition is "+ endPosition);//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 (con.getResponseCode() != HttpURLConnection.HTTP_OK&& con.getResponseCode() != HttpURLConnection.HTTP_PARTIAL) {System.out.println("Thread " + id + ": code = "+ con.getResponseCode() + ", status = "+ con.getResponseMessage());status = ChildThread.STATUS_HTTPSTATUS_ERROR;this.task.statusError = true;outputStream.close();con.disconnect();System.out.println("Thread " + id + " finished.");//递减锁存器的计数，如果计数到达零，则释放所有等待的线程。latch.countDown();break;}inputStream = con.getInputStream();int len = 0;byte[] b = new byte[1024];while (!this.task.statusError&& (len = inputStream.read(b)) != -1) {outputStream.write(b, 0, len);count += len;startPosition += len;// 每读满4096个byte（一个内存页），往磁盘上flush一下if (count % 4096 == 0) {outputStream.flush();}}if (count >= threadDownloadLength) {status = ChildThread.STATUS_HAS_FINISHED;}outputStream.flush();outputStream.close();inputStream.close();con.disconnect();} else {status = ChildThread.STATUS_HAS_FINISHED;}System.out.println("Thread " + id + " finished.");latch.countDown();break;} catch (IOException e) {try {outputStream.flush();TimeUnit.SECONDS.sleep(getSleepSeconds());} catch (InterruptedException e1) {e1.printStackTrace();} catch (IOException e2) {e2.printStackTrace();}continue;}}if (outputStream != null) {try {outputStream.close();con.disconnect();} catch (IOException e) {e.printStackTrace();}}}}private void setHeader(URLConnection con) {con.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");con.setRequestProperty("Accept-Language", "en-us,en;q=0.7,zh-cn;q=0.3");con.setRequestProperty("Accept-Encoding", "aa");con.setRequestProperty("Accept-Charset", "ISO-8859-1,utf-8;q=0.7,*;q=0.7");con.setRequestProperty("Keep-Alive", "300");con.setRequestProperty("Connection", "keep-alive");con.setRequestProperty("If-Modified-Since", "Fri, 02 Jan 2009 17:00:05 GMT");con.setRequestProperty("If-None-Match", "\"1261d8-4290-df64d224\"");con.setRequestProperty("Cache-Control", "max-age=0");con.setRequestProperty("Referer", "http://www.skycn.com/soft/14857.html");}public long getSleepSeconds() {return sleepSeconds;}public void setSleepSeconds(long sleepSeconds) {this.sleepSeconds = sleepSeconds;}