Android 中怎么實現(xiàn)多任務(wù)多線程斷點下載功能，很多新手對此不是很清楚，為了幫助大家解決這個難題，下面小編將為大家詳細(xì)講解，有這方面需求的人可以來學(xué)習(xí)下，希望你能有所收獲。

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package com.smart.db;   import java.util.HashMap;   import java.util.Map;   import android.content.Context;   import android.database.Cursor;   import android.database.sqlite.SQLiteDatabase;   /**   * 業(yè)務(wù)bean   *   */   public class FileService {   private DBOpenHelper openHelper;   public FileService(Context context) {     openHelper = new DBOpenHelper(context);   }   /**     * 獲取每條線程已經(jīng)下載的文件長度     * @param path     * @return     */   public Map getData(String path){     SQLiteDatabase db = openHelper.getReadableDatabase();     Cursor cursor = db.rawQuery("select threadid, downlength from SmartFileDownlog where downpath=?", new String[]{path});     Map data = new HashMap();     while(cursor.moveToNext()){      data.put(cursor.getInt(0), cursor.getInt(1));     }     cursor.close();     db.close();     return data;   }   /**     * 保存每條線程已經(jīng)下載的文件長度     * @param path     * @param map     */   public void save(String path,  Map map){//int threadid, int position     SQLiteDatabase db = openHelper.getWritableDatabase();     db.beginTransaction();     try{      for(Map.Entry entry : map.entrySet()){       db.execSQL("insert into SmartFileDownlog(downpath, threadid, downlength) values(?,?,?)",         new Object[]{path, entry.getKey(), entry.getValue()});      }      db.setTransactionSuccessful();     }finally{      db.endTransaction();     }     db.close();   }   /**     * 實時更新每條線程已經(jīng)下載的文件長度     * @param path     * @param map     */   public void update(String path, Map map){     SQLiteDatabase db = openHelper.getWritableDatabase();     db.beginTransaction();     try{      for(Map.Entry entry : map.entrySet()){       db.execSQL("update SmartFileDownlog set downlength=? where downpath=? and threadid=?",         new Object[]{entry.getValue(), path, entry.getKey()});      }      db.setTransactionSuccessful();     }finally{      db.endTransaction();     }     db.close();   }   /**     * 當(dāng)文件下載完成后，刪除對應(yīng)的下載記錄     * @param path     */   public void delete(String path){     SQLiteDatabase db = openHelper.getWritableDatabase();     db.execSQL("delete from SmartFileDownlog where downpath=?", new Object[]{path});     db.close();   }      }   package com.smart.impl;   import java.io.File;   import java.io.RandomAccessFile;   import java.net.HttpURLConnection;   import java.net.URL;   import java.util.LinkedHashMap;   import java.util.Map;   import java.util.UUID;   import java.util.concurrent.ConcurrentHashMap;   import java.util.regex.Matcher;   import java.util.regex.Pattern;   import android.content.Context;   import android.util.Log;   import com.smart.db.FileService;   /**   * 文件下載器   * @author lihuoming@sohu.com   */   public class SmartFileDownloader {   private static final String TAG = "SmartFileDownloader";   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(shù) */   private SmartDownloadThread[] threads;   /* 本地保存文件 */   private File saveFile;   /* 緩存各線程下載的長度*/   private Map data = new ConcurrentHashMap();   /* 每條線程下載的長度 */   private int block;   /* 下載路徑  */   private String downloadUrl;   /**     * 獲取線程數(shù)     */   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 void update(int threadId, int pos) {     this.data.put(threadId, pos);   }   /**     * 保存記錄文件     */   protected synchronized void saveLogFile() {     this.fileService.update(this.downloadUrl, this.data);   }   /**     * 構(gòu)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(shù)     */   public SmartFileDownloader(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 SmartDownloadThread[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(jù)響應(yīng)獲取文件大小       if (this.fileSize <= 0) throw new RuntimeException("Unkown file size ");             String filename = getFileName(conn);       this.saveFile = new File(fileSaveDir, filename);/* 保存文件 */       Map logdata = fileService.getData(downloadUrl);       if(logdata.size()>0){        for(Map.Entry entry : logdata.entrySet())         data.put(entry.getKey(), 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);        }        print("已經(jīng)下載的長度"+ this.downloadSize);       }         }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(rèn)取一個文件名     }     return filename;   }    /**     *  開始下載文件     * @param listener 監(jiān)聽下載數(shù)量的變化,如果不需要了解實時下載的數(shù)量,可以設(shè)置為null     * @return 已下載文件大小     * @throws Exception     */   public int download(SmartDownloadProgressListener 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();//清除數(shù)據(jù)       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 getHttpResponseHeader(HttpURLConnection http) {     Map header = new LinkedHashMap();     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 header = getHttpResponseHeader(http);     for(Map.Entry entry : header.entrySet()){      String key = entry.getKey()!=null ? entry.getKey()+ ":" : "";      print(key+ entry.getValue());     }   }   //打印日志   private static void print(String msg){     Log.i(TAG, msg);   }    }   package com.smart.impl;   import java.io.File;   import java.io.InputStream;   import java.io.RandomAccessFile;   import java.net.HttpURLConnection;   import java.net.URL;   import android.util.Log;   public class SmartDownloadThread extends Thread {   private static final String TAG = "SmartDownloadThread";   private File saveFile;   private URL downUrl;   private int block;   /* *下載開始位置  */   private int threadId = -1;   private int downLength;   private boolean finish = false;   private SmartFileDownloader downloader;   public SmartDownloadThread(SmartFileDownloader 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;   }   @Override   public void run() {     if(downLength < block){//未下載完成      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;//開始位置       int endPos = block * threadId -1;//結(jié)束位置       http.setRequestProperty("Range", "bytes=" + startPos + "-"+ endPos);//設(shè)置獲取實體數(shù)據(jù)的范圍       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);   }   /**     * 下載是否完成     * @return     */   public boolean isFinish() {     return finish;   }   /**     * 已經(jīng)下載的內(nèi)容大小     * @return 如果返回值為-1,代表下載失敗     */   public long getDownLength() {     return downLength;   }   }   package com.smart.activoty.download;   import java.io.File;   import android.app.Activity;   import android.os.Bundle;   import android.os.Environment;   import android.os.Handler;   import android.os.Message;   import android.view.View;   import android.widget.Button;   import android.widget.EditText;   import android.widget.ProgressBar;   import android.widget.TextView;   import android.widget.Toast;   import com.smart.impl.SmartDownloadProgressListener;   import com.smart.impl.SmartFileDownloader;   public class SmartDownloadActivity extends Activity {       private ProgressBar downloadbar;       private EditText pathText;       private TextView resultView;       private Handler handler = new Handler(){     @Override//信息     public void handleMessage(Message msg) {      switch (msg.what) {      case 1:       int size = msg.getData().getInt("size");       downloadbar.setProgress(size);       float result = (float)downloadbar.getProgress()/ (float)downloadbar.getMax();       int p = (int)(result*100);       resultView.setText(p+"%");       if(downloadbar.getProgress()==downloadbar.getMax())        Toast.makeText(SmartDownloadActivity.this, R.string.success, 1).show();       break;      case -1:       Toast.makeText(SmartDownloadActivity.this, R.string.error, 1).show();       break;      }           }            };           @Override       public void onCreate(Bundle savedInstanceState) {           super.onCreate(savedInstanceState);           setContentView(R.layout.main);                      Button button = (Button)this.findViewById(R.id.button);           downloadbar = (ProgressBar)this.findViewById(R.id.downloadbar);           pathText = (EditText)this.findViewById(R.id.path);           resultView = (TextView)this.findViewById(R.id.result);           button.setOnClickListener(new View.OnClickListener() {         @Override      public void onClick(View v) {       String path = pathText.getText().toString();       if(Environment.getExternalStorageState().equals(Environment.MEDIA_MOUNTED)){        File dir = Environment.getExternalStorageDirectory();//文件保存目錄        download(path, dir);       }else{        Toast.makeText(SmartDownloadActivity.this, R.string.sdcarderror, 1).show();       }      }     });       }       //對于UI控件的更新只能由主線程(UI線程)負(fù)責(zé)，如果在非UI線程更新UI控件，更新的結(jié)果不會反映在屏幕上，某些控件還會出錯       private void download(final String path, final File dir){        new Thread(new Runnable() {      @Override      public void run() {       try {        SmartFileDownloader loader = new SmartFileDownloader(SmartDownloadActivity.this, path, dir, 3);        int length = loader.getFileSize();//獲取文件的長度        downloadbar.setMax(length);        loader.download(new SmartDownloadProgressListener(){         @Override         public void onDownloadSize(int size) {//可以實時得到文件下載的長度          Message msg = new Message();          msg.what = 1;          msg.getData().putInt("size", size);                handler.sendMessage(msg);         }});       } catch (Exception e) {        Message msg = new Message();//信息提示        msg.what = -1;        msg.getData().putString("error", "下載失敗");//如果下載錯誤，顯示提示失敗！        handler.sendMessage(msg);       }      }     }).start();//開始             }   }

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