忘了在哪里抄的这东西了，发上来由兴趣的可以去研究一下
public class Task { private String downURL; private String saveFile; private int bufferSize = 64 * 1024; private int workerCount; private int sectionCount; private long contentLength; private long[] sectionsOffset; public static final int HEAD_SIZE = 4096; //读下载描述文件内容 public synchronized void read(RandomAccessFile file) throws IOException { byte[] temp = new byte[HEAD_SIZE]; file.seek(0); int readed = file.read(temp); if (readed != temp.length) { throw new RuntimeException(); } ByteArrayInputStream bais = new ByteArrayInputStream(temp); DataInputStream dis = new DataInputStream(bais); downURL = dis.readUTF(); saveFile = dis.readUTF(); sectionCount = dis.readInt(); contentLength = dis.readLong(); sectionsOffset = new long[sectionCount]; for (int i = 0; i < sectionCount; i++) { sectionsOffset[i] = file.readLong(); } } //创建下载描述文件内容 public synchronized void create(RandomAccessFile file) throws IOException { if (sectionCount != sectionsOffset.length) { throw new RuntimeException(); } long len = HEAD_SIZE + 8 * sectionCount; file.setLength(len); ByteArrayOutputStream baos = new ByteArrayOutputStream(); DataOutputStream dos = new DataOutputStream(baos); dos.writeUTF(downURL); dos.writeUTF(saveFile); dos.writeInt(sectionCount); dos.writeLong(contentLength); byte[] src = baos.toByteArray(); byte[] temp = new byte[HEAD_SIZE]; System.arraycopy(src, 0, temp, 0, src.length); file.seek(0); file.write(temp); writeOffset(file); } //更新下载的过程 public synchronized void writeOffset(RandomAccessFile file) throws IOException { if (sectionCount != sectionsOffset.length) { throw new RuntimeException(); } file.seek(HEAD_SIZE); for (int i = 0; i < sectionsOffset.length; i++) { file.writeLong(sectionsOffset[i]); } } （下面是Getter、Setter） } //这个是下载主程序 public class TaskAssign { public void work(Task task) throws IOException { File file = new File(task.getSaveFile()); if (file.exists()) { return; } //这个是记录是否下载成功。我这里也没有增加失败回复、重试之类的工作。 final AtomicBoolean success = new AtomicBoolean(true); //任务描述文件 File taskFile = new File(task.getSaveFile() + ".r_task"); //真正下载的文件 File saveFile = new File(task.getSaveFile() + ".r_save"); boolean taskFileExist = taskFile.exists(); RandomAccessFile taskRandomFile = null; RandomAccessFile downRandomFile = null; try { taskRandomFile = new RandomAccessFile(taskFile, "rw"); downRandomFile = new RandomAccessFile(saveFile, "rw"); long rtnLen = getContentLength(task.getDownURL()); if (!taskFileExist) { //如果文件不存在，就初始化任务文件和下载文件 task.setContentLength(rtnLen); initTaskFile(taskRandomFile, task); downRandomFile.setLength(rtnLen); } else { //任务文件存在就读取任务文件 task.read(taskRandomFile); if (task.getContentLength() != rtnLen) { throw new RuntimeException(); } } int secCount = task.getSectionCount(); //分配线程去下载，这里用到线程池 ExecutorService es = Executors.newFixedThreadPool(task.getWorkerCount()); for (int i = 0; i < secCount; i++) { final int j = i; final Task t = task; final RandomAccessFile f1 = taskRandomFile; final RandomAccessFile f2 = downRandomFile; es.execute(new Runnable() { public void run() { try { down(f1, f2, t, j); } catch (IOException e) { success.set(false); e.printStackTrace(System.out); } } }); } es.shutdown(); try { es.awaitTermination(24 * 3600, TimeUnit.SECONDS); } catch (InterruptedException e) { e.printStackTrace(); } taskRandomFile.close(); taskRandomFile = null; downRandomFile.close(); downRandomFile = null; //如果下载成功，去掉任务描述文件、帮下载文件改名 if (success.get()) { taskFile.delete(); saveFile.renameTo(file); } } finally { if (taskRandomFile != null) { taskRandomFile.close(); taskRandomFile = null; } if (downRandomFile != null) { downRandomFile.close(); downRandomFile = null; } } } public void down(RandomAccessFile taskRandomFile, RandomAccessFile downRandomFile, Task task, int sectionNo) throws IOException { //这里我用HttpURLConnection下载，你也可以用HttpClient或者自己实现一个Http协议（不过貌似没有必要） URL u = new URL(task.getDownURL()); HttpURLConnection conn = (HttpURLConnection) u.openConnection(); long start = task.getSectionsOffset()[sectionNo]; long end = -1; //这里要注意一下，这里是计算当前块的长度 if (sectionNo < task.getSectionCount() - 1) { long per = task.getContentLength() / task.getSectionCount(); end = per * (sectionNo + 1); } else { end = task.getContentLength(); } if (start >= end) { System.out.println("Section has finished before. " + sectionNo); return; } String range = "bytes=" + start + "-" + (end - 1); conn.setRequestProperty("Range", range); conn.setRequestProperty("User-Agent", "Ray-Downer"); try { conn.connect(); if (conn.getResponseCode() != 206) { throw new RuntimeException(); } if (conn.getContentLength() != (end - start)) { throw new RuntimeException(); } InputStream is = conn.getInputStream(); byte[] temp = new byte[task.getBufferSize()]; BufferedInputStream bis = new BufferedInputStream(is, temp.length); int readed = 0; while ((readed = bis.read(temp)) > 0) { long offset = task.getSectionsOffset()[sectionNo]; synchronized (task) { //下载之后顺便更新描述文件，你可能会发现这里效率比较低，在一个线程同步里进行两次文件操作。你可以自己实现一个缓冲写。 downRandomFile.seek(offset); downRandomFile.write(temp, 0, readed); offset += readed; task.getSectionsOffset()[sectionNo] = offset; task.writeOffset(taskRandomFile); } } } finally { conn.disconnect(); } System.out.println("Section finished. " + sectionNo); } public void initTaskFile(RandomAccessFile taskRandomFile, Task task) throws IOException { int secCount = task.getSectionCount(); long per = task.getContentLength() / secCount; long[] sectionsOffset = new long[secCount]; for (int i = 0; i < secCount; i++) { sectionsOffset[i] = per * i; } task.setSectionsOffset(sectionsOffset); task.create(taskRandomFile); } public long getContentLength(String url) throws IOException { URL u = new URL(url); HttpURLConnection conn = (HttpURLConnection) u.openConnection(); try { return conn.getContentLength(); } finally { conn.disconnect(); } } } //稍微测试一下。 public class Main { public static void main(String[] args) throws IOException { test3(); System.out.println("\n\n===============\nFinished."); } public static void test1() throws IOException { Task task = new Task(); task.setDownURL("http://61.152.235.21/qqfile/qq/2007iistable/QQ2007IIKB1.exe"); task.setSaveFile("H:/Test2.exe"); task.setSectionCount(200); task.setWorkerCount(100); task.setBufferSize(256 * 1024); TaskAssign ta = new TaskAssign(); ta.work(task); } public static void test2() throws IOException { Task task = new Task(); task.setDownURL("http://student1.scut.edu.cn:8880/manage/news/data/1208421861893.xls"); task.setSaveFile("H:/Test3.xls"); task.setSectionCount(5); task.setWorkerCount(1); task.setBufferSize(128 * 1024); TaskAssign ta = new TaskAssign(); ta.work(task); } public static void test3() throws IOException { Task task = new Task(); task.setDownURL("http://go.microsoft.com/fwlink/?linkid=57034"); task.setSaveFile("H:/vc2005express.iso"); task.setSectionCount(500); task.setWorkerCount(200); task.setBufferSize(128 * 1024); TaskAssign ta = new TaskAssign(); ta.work(task); } public static void test4() throws IOException { Task task = new Task(); task.setDownURL("http://down.sandai.net/Thunder5.7.9.472.exe"); task.setSaveFile("H:/Thunder.exe"); task.setSectionCount(30); task.setWorkerCount(30); task.setBufferSize(128 * 1024); TaskAssign ta = new TaskAssign(); ta.work(task); } }
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