android应用多线程和http断点续传下载数据断点续传的原理很简单，就是在Http的请求上和一般的下载有所不同
android应用多线程和http断点续传下载数据
断点续传的原理很简单，就是在Http的请求上和一般的下载有所不同而已。注：需要web容器的支持，现在绝大多数都支持此项
以例子说明断点续传。
例如使用本地的服务器127.0.0.1，文件名为data.zip。下载该文件所发出的头信息如下：
GET /data.zip HTTP/1.1 Accept: image/gif, image/x-xbitmap, image/jpeg, image/pjpeg, application/vnd.ms-excel, application/msword, application/vnd.ms-powerpoint, */* Accept-Language: zh-cn Accept-Encoding: gzip, deflate User-Agent: Mozilla/4.0 (compatible; MSIE 5.01; Windows NT 5.0) Connection: Keep-Alive在服务器端接收到请求后，会按要求寻找请求的文件，并提取文件的信息，然后返回给浏览器，返回信息如下：
200 Content-Length=105555555 Accept-Ranges=bytes Date=Sun, 28 Aug 2012 10:56:16 GMT ETag=W/"031a54e173c11:df5" Content-Type=application/octet-stream Server=Apache/1.3.14(Unix)Last-Modified= Sun, 28 Aug 2012 10:56:16 GMT断点续传，就是要将文件从已经下载的地方开始，继续下载。所在客户端在发给服务器的信息中，要指明下载开始的地方。
下面是用自己模拟一个"浏览器"来传递请求信息给Web服务器，要求从20120828字节开始。
GET /data.zip HTTP/1.0 User-Agent: Mozilla/4.0 (compatible; MSIE 5.01; Windows NT 5.0)RANGE: bytes=20120828-
请仔细查看一下，就会发现上面多了一行RANGE: bytes=20120828- 的信息
这一行的意思是告诉服务器下载data.zip这个文件从20120828字节开始传，前面的字节就不需要用传了。
服务器收到这个请求以后，返回的信息如下：
206 Content-Length=105555555Content-Range=bytes 20120828-105555554/105555555Date= Sun, 28 Aug 2012 11:04:18 GMT ETag=W/"031a54e173c11:df5" Content-Type=application/octet-stream Server=Apache/1.3.14(Unix) Last-Modified= Sun, 28 Aug 2012 10:56:16 GMT和前面服务器返回的信息比较一下，就会发现增加了一行：
Content-Range=bytes 20120828-10555554/10555555
返回的代码也改为206了，而不再是200了。
知道了以上原理，就可以进行断点续传的编程了。
至于多线程，不多做介绍了，以下是实现的多线程断点续的部分代码：
文件下载类的主要代码
private static final String TAG = "FileDownloader";private Context context;private DownloadDao downloadDao;/* 已下载文件长度 */private int downloadSize = 0;/* 原始文件长度 */private int fileSize = 0;/* 线程数 */private DownloadThread[] threads;/* 本地保存文件 */private File saveFile;/* 缓存各线程下载的长度*/private Map<Integer, Integer> data = new ConcurrentHashMap<Integer, Integer>();/* 每条线程下载的长度 */private int block;/* 下载路径 */private String downloadUrl;/* 压缩包名称 */private String filename;/** * 构建文件下载器 * @param downloadUrl 下载路径 * @param fileSaveDir 文件保存目录 * @param threadNum 下载线程数 */public FileDownloader(Context context, String downloadUrl, File fileSaveDir, int threadNum) {try {this.context = context;this.downloadUrl = downloadUrl;downloadDao = new DownloadDao(this.context);URL url = new URL(this.downloadUrl);if(!fileSaveDir.exists()) fileSaveDir.mkdirs();this.threads = new DownloadThread[threadNum];HttpURLConnection conn = (HttpURLConnection) url.openConnection();conn.setConnectTimeout(10*1000);//conn.setReadTimeout(50*1000);conn.setRequestMethod("GET");conn.setRequestProperty("Accept", "image/gif, image/jpeg, image/pjpeg, image/pjpeg, application/x-shockwave-flash, application/xaml+xml, application/vnd.ms-xpsdocument, application/x-ms-xbap, application/x-ms-application, application/vnd.ms-excel, application/vnd.ms-powerpoint, application/msword, */*");conn.setRequestProperty("Accept-Language", "zh-CN");conn.setRequestProperty("Referer", downloadUrl); conn.setRequestProperty("Charset", "UTF-8");conn.setRequestProperty("User-Agent", "Mozilla/4.0 (compatible; MSIE 8.0; Windows NT 5.2; Trident/4.0; .NET CLR 1.1.4322; .NET CLR 2.0.50727; .NET CLR 3.0.04506.30; .NET CLR 3.0.4506.2152; .NET CLR 3.5.30729)");conn.setRequestProperty("Connection", "Keep-Alive");conn.connect();printResponseHeader(conn);Log.w("conn.getResponseCode()",String.valueOf(conn.getResponseCode()));if (conn.getResponseCode()==200) {this.fileSize = conn.getContentLength();//根据响应获取文件大小if (this.fileSize <= 0) throw new RuntimeException("Unkown file size ");this.filename = getFileName(conn);this.saveFile = new File(fileSaveDir, filename);/* 保存文件 */ArrayList<Map<String,String>> logdata = downloadDao.getData(downloadUrl);if(logdata.size()>0){for(int i=0; i<logdata.size(); i++){int threadId = 0;int pos = 0;for(Map.Entry<String, String> entry : logdata.get(i).entrySet()){if(entry.getKey().equals("THREADID")){threadId = Integer.parseInt(entry.getValue());}else{pos = Integer.parseInt(entry.getValue());}}data.put(threadId,pos);}//for(Map.Entry<String, String> entry : logdata.get(0).entrySet())//data.put(Integer.parseInt(entry.getKey()), Integer.parseInt(entry.getValue()));}this.block = (this.fileSize % this.threads.length)==0? this.fileSize / this.threads.length : this.fileSize / this.threads.length + 1;if(this.data.size()==this.threads.length){for (int i = 0; i < this.threads.length; i++) {this.downloadSize += this.data.get(i+1);}Log.w(TAG, "已经下载的长度"+ this.downloadSize);}}else{throw new RuntimeException("server no response ");}} catch (Exception e) {Log.w(TAG, e.getMessage());throw new RuntimeException("don't connection this url");}}/** * 获取文件名 */private String getFileName(HttpURLConnection conn) {String filename = this.downloadUrl.substring(this.downloadUrl.lastIndexOf('/') + 1);if(filename==null || "".equals(filename.trim())){//如果获取不到文件名称for (int i = 0;; i++) {String mine = conn.getHeaderField(i);if (mine == null) break;if("content-disposition".equals(conn.getHeaderFieldKey(i).toLowerCase())){Matcher m = Pattern.compile(".*filename=(.*)").matcher(mine.toLowerCase());if(m.find()) return m.group(1);}}filename = UUID.randomUUID()+ ".tmp";//默认取一个文件名}return filename;}/** * 开始下载文件 * @param listener 监听下载数量的变化,如果不需要了解实时下载的数量,可以设置为null * @return 已下载文件大小 * @throws Exception */public int download(DownloadProgressListener listener) throws Exception{try {RandomAccessFile randOut = new RandomAccessFile(this.saveFile, "rw");if(this.fileSize>0) randOut.setLength(this.fileSize);randOut.close();URL url = new URL(this.downloadUrl);if(this.data.size() != this.threads.length){this.data.clear();for (int i = 0; i < this.threads.length; i++) {this.data.put(i+1, 0);}}for (int i = 0; i < this.threads.length; i++) {int downLength = this.data.get(i+1);if(downLength < this.block && this.downloadSize<this.fileSize){ //该线程未完成下载时,继续下载this.threads[i] = new DownloadThread(this, url, this.saveFile, this.block, this.data.get(i+1), i+1);this.threads[i].setPriority(7);this.threads[i].start();}else{this.threads[i] = null;}}this.downloadDao.saveData(this.downloadUrl, this.data);boolean notFinish = true;//下载未完成while (notFinish) {// 循环判断是否下载完毕Thread.sleep(900);notFinish = false;//假定下载完成for (int i = 0; i < this.threads.length; i++){if (this.threads[i] != null && !this.threads[i].isFinish()) {notFinish = true;//下载没有完成if(this.threads[i].getDownLength() == -1){//如果下载失败,再重新下载this.threads[i] = new DownloadThread(this, url, this.saveFile, this.block, this.data.get(i+1), i+1);this.threads[i].setPriority(7);this.threads[i].start();}}}Log.w("this.downloadSize", String.valueOf(this.downloadSize));Log.w("this.fileSize", String.valueOf(this.fileSize));if(this.downloadSize==this.fileSize){//解压zip文件/*listener.onDownloadSize(this.downloadSize,true);String unZipfileName=this.saveFile.getPath();//压缩文件路径this.unZip(unZipfileName, this.tempPath);listener.onDownloadSize(this.downloadSize,false);*/listener.onDownloadSize(this.downloadSize,false);String unZipfileName=this.saveFile.getPath();//压缩文件路径this.unZip(unZipfileName, this.tempPath);listener.onDownloadSize(this.downloadSize,true);}else{listener.onDownloadSize(this.downloadSize,false);}}downloadDao.deleteData(this.downloadUrl);} catch (Exception e) {Log.w(TAG, e.getMessage());throw new Exception("file download fail");}return this.downloadSize;}/** * 获取Http响应头字段 * @param http * @return */public static Map<String, String> getHttpResponseHeader(HttpURLConnection http) {Map<String, String> header = new LinkedHashMap<String, String>();for (int i = 0;; i++) {String mine = http.getHeaderField(i);if (mine == null) break;header.put(http.getHeaderFieldKey(i), mine);}return header;}/** * 打印Http头字段 * @param http */public static void printResponseHeader(HttpURLConnection http){Map<String, String> header = getHttpResponseHeader(http);for(Map.Entry<String, String> entry : header.entrySet()){String key = entry.getKey()!=null ? entry.getKey()+ ":" : "";Log.w(TAG, key+ entry.getValue());}}下载的线程类的主要代码
/** * 下载线程类 * @author zhaidi * */public class DownloadThread extends Thread {private static final String TAG = "DownloadThread";private File saveFile;private URL downUrl;private int block;/* 下载开始位置 */private int threadId = -1;private int downLength;private boolean finish = false;private FileUpOrDown downloader;//private FileUpdater updater;public DownloadThread(FileDownloader downloader, URL downUrl, File saveFile, int block, int downLength, int threadId) {this.downUrl = downUrl;this.saveFile = saveFile;this.block = block;this.downloader = downloader;this.threadId = threadId;this.downLength = downLength;}public DownloadThread(FileUpdater updater, URL downUrl, File saveFile, int block, int downLength, int threadId) {this.downUrl = downUrl;this.saveFile = saveFile;this.block = block;this.downloader = updater;this.threadId = threadId;this.downLength = downLength;}@Overridepublic void run() {if(downLength < block){//未下载完成try {HttpURLConnection http = (HttpURLConnection) downUrl.openConnection();http.setConnectTimeout(5 * 1000);http.setRequestMethod("GET");http.setRequestProperty("Accept", "image/gif, image/jpeg, image/pjpeg, image/pjpeg, application/x-shockwave-flash, application/xaml+xml, application/vnd.ms-xpsdocument, application/x-ms-xbap, application/x-ms-application, application/vnd.ms-excel, application/vnd.ms-powerpoint, application/msword, */*");http.setRequestProperty("Accept-Language", "zh-CN");http.setRequestProperty("Referer", downUrl.toString()); http.setRequestProperty("Charset", "UTF-8");int startPos = block * (threadId - 1) + downLength;//开始位置int endPos = block * threadId -1;//结束位置http.setRequestProperty("Range", "bytes=" + startPos + "-"+ endPos);//设置获取实体数据的范围http.setRequestProperty("User-Agent", "Mozilla/4.0 (compatible; MSIE 8.0; Windows NT 5.2; Trident/4.0; .NET CLR 1.1.4322; .NET CLR 2.0.50727; .NET CLR 3.0.04506.30; .NET CLR 3.0.4506.2152; .NET CLR 3.5.30729)");http.setRequestProperty("Connection", "Keep-Alive");InputStream inStream = http.getInputStream();byte[] buffer = new byte[1024];int offset = 0;print("Thread " + this.threadId + " start download from position "+ startPos);RandomAccessFile threadfile = new RandomAccessFile(this.saveFile, "rwd");threadfile.seek(startPos);while ((offset = inStream.read(buffer, 0, 1024)) != -1) {threadfile.write(buffer, 0, offset);downLength += offset;downloader.update(this.threadId, downLength);downloader.saveLogFile();downloader.append(offset);}threadfile.close();inStream.close();print("Thread " + this.threadId + " download finish");this.finish = true;} catch (Exception e) {this.downLength = -1;print("Thread "+ this.threadId+ ":"+ e);}}}private static void print(String msg){Log.i(TAG, msg);}/** * 下载是否完成 * @return */public boolean isFinish() {return finish;}/** * 已经下载的内容大小 * @return 如果返回值为-1,代表下载失败 */public long getDownLength() {return downLength;}}下载的调用如下：
其中downloadbar是一个进度条控件，SpecialActivity则是android中的一个控件
FileDownloader loader = new FileDownloader(SpecialActivity.this, path, dir, 5);int length = loader.getFileSize();//获取文件的长度downloadbar.setMax(length);loader.download(new DownloadProgressListener(){@Override/*public void onDownloadSize(int size) {//可以实时得到文件下载的长度Message msg = new Message();msg.what = 1;msg.getData().putInt("size", size);handler.sendMessage(msg);}});*/public void onDownloadSize(int size,boolean upzip) {//可以实时得到文件下载的长度Message msg = new Message();msg.what = 1;msg.getData().putInt("size", size);handler.sendMessage(msg);}});