Android通過HTTP協議實現斷點續傳下載

/ public class FileDownloader { private static final String TAG = "FileDownloader"; private Context context; private FileService fileService;
/ 已下載文件長度 / private int downloadSize = 0; / 原始文件長度 / private int fileSize = 0; / 線程數 / private DownloadThread[] threads; / 本地保存文件 / private File saveFile; / 緩存各線程下載的長度/ private Map<Integer, Integer> data = new ConcurrentHashMap<Integer, Integer>(); / 每條線程下載的長度 / private int block; / 下載路徑 */ private String downloadUrl; /**

• 獲取線程數 */ public int getThreadSize() { return threads.length; } /**
• 獲取文件大小
• @return */ public int getFileSize() { return fileSize; } /**
• 累計已下載大小
• @param size */ protected synchronized void append(int size) { downloadSize += size; } /**
• 更新指定線程最后下載的位置
• @param threadId 線程id
• @param pos 最后下載的位置 */ protected synchronized void update(int threadId, int pos) { this.data.put(threadId, pos); this.fileService.update(this.downloadUrl, this.data); } /**
• 構建文件下載器
• @param downloadUrl 下載路徑
• @param fileSaveDir 文件保存目錄

• @param threadNum 下載線程數 */ public FileDownloader(Context context, String downloadUrl, File fileSaveDir, int threadNum) { try {

   this.context = context;
   this.downloadUrl = downloadUrl;
   fileService = new FileService(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(5*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);
   if (conn.getResponseCode()==200) {
       this.fileSize = conn.getContentLength();//根據響應獲取文件大小
       if (this.fileSize <= 0) throw new RuntimeException("Unkown file size ");
  
       String filename = getFileName(conn);//獲取文件名稱
       this.saveFile = new File(fileSaveDir, filename);//構建保存文件
       Map<Integer, Integer> logdata = fileService.getData(downloadUrl);//獲取下載記錄
       if(logdata.size()>0){//如果存在下載記錄
           for(Map.Entry<Integer, Integer> entry : logdata.entrySet())
               data.put(entry.getKey(), entry.getValue());//把各條線程已經下載的數據長度放入data中
       }
       if(this.data.size()==this.threads.length){//下面計算所有線程已經下載的數據長度
           for (int i = 0; i < this.threads.length; i++) {
               this.downloadSize += this.data.get(i+1);
           }
           print("已經下載的長度"+ this.downloadSize);
       }
       //計算每條線程下載的數據長度
       this.block = (this.fileSize % this.threads.length)==0? this.fileSize / this.threads.length : this.fileSize / this.threads.length + 1;
   }else{
       throw new RuntimeException("server no response ");
   }
  

  } catch (Exception e) {

   print(e.toString());
   throw new RuntimeException("don't connection this url");
  

  } } /**

• 獲取文件名 */ private String getFileName(HttpURLConnection conn) { String filename = this.downloadUrl.substring(this.downloadUrl.lastIndexOf('/') + 1); if(filename==null || "".equals(filename.trim())){//如果獲取不到文件名稱

   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";//默認取一個文件名
  

  } return filename; }

  /**

• 開始下載文件
• @param listener 監聽下載數量的變化,如果不需要了解實時下載的數量,可以設置為null
• @return 已下載文件大小
• @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);//初始化每條線程已經下載的數據長度為0
       }
   }
   for (int i = 0; i < this.threads.length; i++) {//開啟線程進行下載
       int downLength = this.data.get(i+1);
       if(downLength < this.block && this.downloadSize<this.fileSize){//判斷線程是否已經完成下載,否則繼續下載  
           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.fileService.save(this.downloadUrl, this.data);
   boolean notFinish = true;//下載未完成
   while (notFinish) {// 循環判斷所有線程是否完成下載
       Thread.sleep(900);
       notFinish = false;//假定全部線程下載完成
       for (int i = 0; i < this.threads.length; i++){
           if (this.threads[i] != null && !this.threads[i].isFinish()) {//如果發現線程未完成下載
               notFinish = true;//設置標志為下載沒有完成
               if(this.threads[i].getDownLength() == -1){//如果下載失敗,再重新下載
                   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();
               }
           }
       }               
       if(listener!=null) listener.onDownloadSize(this.downloadSize);//通知目前已經下載完成的數據長度
   }
   fileService.delete(this.downloadUrl);
  

  } catch (Exception e) {

   print(e.toString());
   throw new Exception("file download fail");
  

  } return this.downloadSize; } /**
• 獲取Http響應頭字段
• @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頭字段

• @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()+ ":" : "";
   print(key+ entry.getValue());
  

  } }

  private static void print(String msg){ Log.i(TAG, msg); } }</pre>

  DownloadThread.java

  package cn.itcast.net.download;