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[Java教程]安卓开发笔记——关于文件断点续传


什么是断点续传?

客户端软件断点续传指的是在下载或上传时,将下载或上传任务(一个文件或一个压缩包)人为的划分为几个部分,每一个部分采用一个线程进行上传或下载,如果碰到网络故障,可以从已经上传或下载的部分开始继续上传下载未完成的部分,而没有必要从头开始上传下载。用户可以节省时间,节省流量,也提高速度。

 

我写了个小Demo,先看下实现效果图:

  

断点续传的原理?

断点续传其实并没有那么神秘,它只不过是利用了HTTP传输协议中请求头(REQUEST HEADER)的不同来进行断点续传的。

 

以下是我刚在百度音乐下载MP3的时候用Firebug截下来的HTTP请求头:

Accept:image/webp,*/*;q=0.8Accept-Encoding:gzip, deflate, sdchAccept-Language:zh-CN,zh;q=0.8Connection:keep-aliveCookie:BIDUPSID=6B8AF721169ED82B182A7EE22F75BB87; BAIDUID=6B8AF721169ED82B182A7EE22F75BB87:FG=1; BDUSS=1pWS14dzl6Ry02MVJoN0toT1RlTzRIdkdBRVlsN1JJdG9OVmQ5djAybTJ1a1JWQVFBQUFBJCQAAAAAAAAAAAEAAACkSkgjTXJfTGVlX-fiAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAALYtHVW2LR1VaW; __xsptplus188=188.1.1428024707.1428024712.2%234%7C%7C%7C%7C%7C%23%23QdAfR9H5KZHSIGakiCWebLQCd6CjKjz5%23; locale=zh; cflag=65279%3A3; BDRCVFR[-z8N-kPXoJt]=I67x6TjHwwYf0; H_PS_PSSID=11099_13386_1439_13425_13075_10902_12953_12868_13320_12691_13410_12722_12737_13085_13325_13203_12835_13161_8498Host:b.hiphotos.baidu.comReferer:http://music.baidu.com/song/124380645User-Agent:Mozilla/5.0 (Windows NT 6.1; WOW64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/39.0.2171.95 Safari/537.36

这是百度音乐服务器给我返回的信息:

Age:347651Cache-Control:max-age=31536000Connection:keep-aliveContent-Length:16659Content-Type:image/jpegDate:Sat, 11 Apr 2015 06:48:45 GMTError-Message:OKETag:"10487865676202532488"Expires:Wed, 06 Apr 2016 06:02:50 GMTLast-Modified:Tue, 07 Apr 2015 05:45:32 GMTOhc-Cachable:1Server:JSP3/2.0.7

这是一般的下载请求,服务器会给我们返回我们请求下载文件的长度(Content-Length),成功状态码为:200。

而断点续传是要从我们之前已经下载好的文件位置继续上一次的传输,顾名思义我们需要告诉服务器我们上一次已经下载到哪里了,所以在我们的HTTP请求头里要额外的包含一条信息,而这也就是断点续传的奥秘所在了。

这条信息为:(RANGE为请求头属性,X为从什么地方开始,Y为到什么地方结束)

RANGE: bytes=X-Y 

例如:

Range : 用于客户端到服务器端的请求,可通过该字段指定下载文件的某一段大小,及其单位。典型的格式如:
Range: bytes=0-499 下载第0-499字节范围的内容
Range: bytes=500-999 下载第500-999字节范围的内容
Range: bytes=-500 下载最后500字节的内容
Range: bytes=500- 下载从第500字节开始到文件结束部分的内容

 

以上是HTTP需要注意的地方,接下来讲讲Java里需要注意的几个类

关于这个HTTP请求,在Java的Net包下,给我们封装好了一系列的类,我们直接拿来使用就行了。

这是java.net.URLConnection类下的一个方法,用来设置HTTP请求头的,Key对应HTTP请求头属性,Value对应请求头属性的值。

这是java.io.RandomAccessFile类,这个类的实例支持对随机访问文件的读取和写入,这个类里有个很重要的seek(long pos)方法,

这个方法可以在你设置的长度的下一个位置进行写入,例如seek(599),那么系统下一次写入的位置就是该文件的600位置。

 

既然是断点续传,那么我们自身肯定也要记录断点位置,所以这里数据库也是必不可少的。

 

具体实现:

好了,了解了上面的知识点后,可以开始动手写程序了。

下面是我写的一个小Demo,用单线程来实现的断点续传的,注释非常全。

 这是Demo的结构图:(实在不会画图,凑合着看哈)

主类(Activity):

 1 package com.example.ui; 2  3 import android.app.Activity; 4 import android.app.AlertDialog; 5 import android.app.ProgressDialog; 6 import android.app.AlertDialog.Builder; 7 import android.content.BroadcastReceiver; 8 import android.content.Context; 9 import android.content.DialogInterface; 10 import android.content.Intent; 11 import android.content.IntentFilter; 12 import android.os.Bundle; 13 import android.util.Log; 14 import android.view.View; 15 import android.view.View.OnClickListener; 16 import android.widget.Button; 17 import android.widget.ProgressBar; 18 import android.widget.TextView; 19  20 import com.example.downloadfiletest.R; 21 import com.example.entity.FileInfo; 22 import com.example.logic.DownloadService; 23  24 public class MainActivity extends Activity { 25  26   private TextView textView; 27   private ProgressBar progressBar; 28   private Button bt_start; 29   private Button bt_stop; 30  31   @Override 32   protected void onCreate(Bundle savedInstanceState) { 33     super.onCreate(savedInstanceState); 34     setContentView(R.layout.activity_main); 35     initView(); // 初始化控件 36  37     // 注册广播接收者 38     IntentFilter intentFilter = new IntentFilter(); 39     intentFilter.addAction(DownloadService.UPDATE); 40     registerReceiver(broadcastReceiver, intentFilter); 41  42   } 43  44   @Override 45   protected void onDestroy() { 46     super.onDestroy(); 47     // 解绑 48     unregisterReceiver(broadcastReceiver); 49   } 50  51   // 初始化控件 52   private void initView() { 53     textView = (TextView) findViewById(R.id.textView); 54     progressBar = (ProgressBar) findViewById(R.id.progressBar); 55     bt_start = (Button) findViewById(R.id.bt_start); 56     bt_stop = (Button) findViewById(R.id.bt_stop); 57     progressBar.setMax(100); 58  59     final FileInfo fileInfo = new FileInfo(0, "Best Of Joy.MP3-Michael Jackson", "http://music.baidu.com/data/music/file?link=http://yinyueshiting.baidu.com/data2/music/38264529/382643441428735661128.mp3?xcode=46e7c02e3acba184b6145f688bb9f2422c866f9e4969f410&song_id=38264344", 0, 0); 60  61     // 点击开始下载 62     bt_start.setOnClickListener(new OnClickListener() { 63  64       @Override 65       public void onClick(View v) { 66         Intent intent = new Intent(MainActivity.this, DownloadService.class); 67         intent.setAction(DownloadService.START); 68         intent.putExtra("FileInfo", fileInfo); 69         startService(intent); 70         textView.setText("正在下载文件:" + fileInfo.getFileName()); 71  72       } 73     }); 74  75     // 点击停止下载 76     bt_stop.setOnClickListener(new OnClickListener() { 77  78       @Override 79       public void onClick(View v) { 80         Intent intent = new Intent(MainActivity.this, DownloadService.class); 81         intent.setAction(DownloadService.STOP); 82         intent.putExtra("FileInfo", fileInfo); 83         startService(intent); 84         textView.setText("任务已暂停,请点击下载继续"); 85       } 86     }); 87  88   } 89  90   // 广播接收者 91   BroadcastReceiver broadcastReceiver = new BroadcastReceiver() { 92  93     @Override 94     public void onReceive(Context context, Intent intent) { 95       if (intent.getAction().equals(DownloadService.UPDATE)) { 96         int finished = intent.getIntExtra("finished", 0); 97         progressBar.setProgress(finished); 98          99         //用户界面友好,提醒用户任务下载完成100         if (finished ==100) {101           AlertDialog.Builder builder=new AlertDialog.Builder(MainActivity.this);102           builder.setTitle("任务状态");103           builder.setMessage("文件下载已完成!");104           builder.setPositiveButton("确认", new DialogInterface.OnClickListener() {105             106             @Override107             public void onClick(DialogInterface dialog, int which) {108                   progressBar.setProgress(0);109                   textView.setText("请点击下载");110             }111           });112           builder.show();113         }114       }115     }116   };117 }

后台服务类(Service)

 1 package com.example.logic; 2  3 import java.io.File; 4 import java.io.IOException; 5 import java.io.RandomAccessFile; 6 import java.net.HttpURLConnection; 7 import java.net.URL; 8  9 import org.apache.http.HttpStatus; 10 import org.apache.http.client.ClientProtocolException; 11  12 import android.app.Service; 13 import android.content.Intent; 14 import android.os.Environment; 15 import android.os.Handler; 16 import android.os.IBinder; 17 import android.util.Log; 18  19 import com.example.entity.FileInfo; 20  21 public class DownloadService extends Service { 22  23   // 按钮标志符 24   public static final String START = "START"; 25   public static final String STOP = "STOP"; 26   // 更新进度标志 27   public static final String UPDATE = "UPDATE"; 28   // 下载路径(内存卡(SD)根目录下的/downloads/) 29   public static final String DOWNLOADPATH = Environment.getExternalStorageDirectory().getAbsolutePath() + "/downloads/"; 30   // 定义初始化文件操作标志 31   public static final int INIT = 0; 32  33   private DownloadTask downloadTask; 34  35   private Handler handler = new Handler() { 36     public void handleMessage(android.os.Message msg) { 37       switch (msg.what) { 38       case INIT: 39         FileInfo fileInfo = (FileInfo) msg.obj; 40         Log.i("init", fileInfo.toString()); 41         // 进行下载任务操作 42         downloadTask = new DownloadTask(DownloadService.this, fileInfo); 43         downloadTask.download(); 44         break; 45       } 46     }; 47   }; 48  49   /** 50    * 当Service启动时会被调用,用来接收Activity传送过来的数据 51   */ 52   @Override 53   public int onStartCommand(Intent intent, int flags, int startId) { 54     if (intent.getAction().equals(START)) { 55       // 当点击开始下载操作时 56       // 接收Activity(putExtra)过来的数据 57       FileInfo fileInfo = (FileInfo) intent.getSerializableExtra("FileInfo"); 58       Log.i(START, fileInfo.toString()); 59       new Thread(new InitFileThread(fileInfo)).start(); 60  61     } else if (intent.getAction().equals(STOP)) { 62       // 当点击停止下载操作时 63       FileInfo fileInfo = (FileInfo) intent.getSerializableExtra("FileInfo"); 64       Log.i(STOP, fileInfo.toString()); 65       // 暂定任务 66       if (downloadTask != null) { 67         downloadTask.flag = true; 68       } 69     } 70  71     return super.onStartCommand(intent, flags, startId); 72   } 73  74   @Override 75   public IBinder onBind(Intent intent) { 76     return null; 77   } 78  79   // 初始化文件操作获取网络资源大小长度,开辟子线程 80   class InitFileThread implements Runnable { 81  82     private FileInfo fileInfo; 83  84     // 构造方法,获取文件对象 85     public InitFileThread(FileInfo fileInfo) { 86       this.fileInfo = fileInfo; 87     } 88  89     @Override 90     public void run() { 91       /* 92        * 1、打开网络连接,获取文件长度 2、创建本地文件,长度和网络文件相等 93       */ 94       HttpURLConnection httpURLConnection = null; 95       RandomAccessFile randomAccessFile = null; 96       try { 97         URL url = new URL(fileInfo.getUrl()); 98         httpURLConnection = (HttpURLConnection) url.openConnection(); 99         // 知识点:除了下载文件,其他一律用POST100         httpURLConnection.setConnectTimeout(3000);101         httpURLConnection.setRequestMethod("GET");102         // 定义文件长度103         int length = -1;104         // 网络连接成功105         if (httpURLConnection.getResponseCode() == HttpStatus.SC_OK) {106           length = httpURLConnection.getContentLength();107         }108         // 判断是否取得文件长度109         if (length <= 0) {110           return;111         }112 113         // 创建文件目录对象114         File dir = new File(DOWNLOADPATH);115         if (!dir.exists()) {116           // 若目录不存在,创建117           dir.mkdir();118         }119         // 创建文件对象120         File file = new File(dir, fileInfo.getFileName());121         // 创建随机访问文件流 参数二为权限:读写删122         randomAccessFile = new RandomAccessFile(file, "rwd");123         randomAccessFile.setLength(length);124         fileInfo.setLength(length);125         // 发送handler126         handler.obtainMessage(INIT, fileInfo).sendToTarget();127 128       } catch (ClientProtocolException e) {129         e.printStackTrace();130       } catch (IOException e) {131         e.printStackTrace();132       } finally {133         if (randomAccessFile != null) {134           try {135             randomAccessFile.close();136           } catch (IOException e) {137             e.printStackTrace();138           }139         }140       }141 142     }143 144   }145 146 }

下载任务类:

 1 package com.example.logic; 2  3 import java.io.File; 4 import java.io.IOException; 5 import java.io.InputStream; 6 import java.io.RandomAccessFile; 7 import java.net.HttpURLConnection; 8 import java.net.MalformedURLException; 9 import java.net.URL; 10 import java.util.List; 11  12 import org.apache.http.HttpStatus; 13  14 import android.content.Context; 15 import android.content.Intent; 16 import android.util.Log; 17  18 import com.example.dao.ThreadDAO; 19 import com.example.dao.ThreadDAOImpl; 20 import com.example.entity.FileInfo; 21 import com.example.entity.ThreadInfo; 22  23 /** 24  * 下载任务类 25  *  26  * @author Balla_兔子 27  *  28 */ 29 public class DownloadTask { 30   private Context context; 31   private ThreadDAO dao; 32   private FileInfo fileInfo; 33   // 初始化下载进度,默认为0 34   private int finished = 0; 35  36   // 是否暂停下载标识符 37   public boolean flag = false; 38  39   public DownloadTask(Context context, FileInfo fileInfo) { 40     this.context = context; 41     this.fileInfo = fileInfo; 42     dao = new ThreadDAOImpl(context); 43   } 44  45   public void download() { 46     // 线程信息的url和文件的url对应 47     List<ThreadInfo> threadInfos = dao.getThreadInfo(fileInfo.getUrl()); 48     ThreadInfo threadInfo = null; 49     if (threadInfos.size() == 0) { 50       // 若数据库无此线程任务 51       threadInfo = new ThreadInfo(0, fileInfo.getUrl(), 0, fileInfo.getLength(), 0); 52     } else { 53       threadInfo = threadInfos.get(0); 54     } 55     // 创建子线程进行下载 56     new Thread(new DownloadThread(threadInfo)).start(); 57   } 58  59   // 执行下载任务,开辟子线程 60   class DownloadThread implements Runnable { 61  62     private ThreadInfo threadInfo; 63  64     public DownloadThread(ThreadInfo threadInfo) { 65       this.threadInfo = threadInfo; 66     } 67  68     @Override 69     public void run() { 70       HttpURLConnection urlConnection = null; 71       InputStream inputStream = null; 72       RandomAccessFile randomAccessFile = null; 73  74       /** 75        * 执行下载任务  76        * 1、查询数据库,确定是否已存在此下载线程,便于继续下载  77        * 2、设置从哪个位置开始下载  78        * 3、设置文件的写入位置 79        * 4、开始下载  80        * 5、广播通知UI更新下载进度  81        * 6、暂停线程的操作  82        * 7、下载完毕,删除数据库信息 83       */ 84       // 1、查询数据库 85       if (!dao.isExists(threadInfo.getUrl(), threadInfo.getThread_id())) { 86         // 若不存在,插入新线程信息 87         dao.insertThread(threadInfo); 88       } 89  90       // 2、设置下载位置 91       try { 92         URL url = new URL(threadInfo.getUrl()); 93         urlConnection = (HttpURLConnection) url.openConnection(); 94         // 设置连接超时时间 95         urlConnection.setConnectTimeout(3000); 96         urlConnection.setRequestMethod("GET"); 97  98         // 设置请求属性 99         // 参数一:Range头域可以请求实体的一个或者多个子范围(一半用于断点续传),如果用户的请求中含有range100         // ,则服务器的相应代码为206。101         // 参数二:表示请求的范围:比如头500个字节:bytes=0-499102 103         // 获取线程已经下载的进度104         int start = threadInfo.getStart() + threadInfo.getFinished();105         urlConnection.setRequestProperty("range", "bytes=" + start + "-" + threadInfo.getEnd());106 107         // 3、设置文件的写入位置108         File file = new File(DownloadService.DOWNLOADPATH, fileInfo.getFileName());109         randomAccessFile = new RandomAccessFile(file, "rwd");110         // 设置从哪里开始写入,如参数为100,那就从101开始写入111         randomAccessFile.seek(start);112 113         finished += threadInfo.getFinished();114         Intent intent = new Intent(DownloadService.UPDATE);115         // 4、开始下载116         if (urlConnection.getResponseCode() == HttpStatus.SC_PARTIAL_CONTENT) {117           inputStream = urlConnection.getInputStream();118           // 设置字节数组缓冲区119           byte[] data = new byte[1024*4];120           // 读取长度121           int len = -1;122           // 取得当前时间123           long time = System.currentTimeMillis();124           while ((len = inputStream.read(data)) != -1) {125             // 读取成功,写入文件126             randomAccessFile.write(data, 0, len);127 128             // 避免更新过快,减缓主线程压力,让其0.5秒发送一次进度129             if (System.currentTimeMillis() - time > 500) {130               time = System.currentTimeMillis();131               // 把当前进度通过广播传递给UI132               finished += len;133               Log.i("finished:", finished+"");134               Log.i("file:", fileInfo.getLength()+"");135               intent.putExtra("finished", finished*100 / fileInfo.getLength());136               context.sendBroadcast(intent);137             }138 139             if (flag) {140               // 暂停下载,更新进度到数据库141               dao.updateThread(threadInfo.getUrl(), threadInfo.getThread_id(), finished);142               // 结束线程143               return;144             }145 146           }147           // 当下载执行完毕时,删除数据库线程信息148           dao.deleteThread(threadInfo.getUrl(), threadInfo.getThread_id());149         }150 151       } catch (MalformedURLException e) {152         e.printStackTrace();153       } catch (IOException e) {154         e.printStackTrace();155       } finally {156         if (urlConnection != null) {157           urlConnection.disconnect();158         }159         if (inputStream != null) {160           try {161             inputStream.close();162           } catch (IOException e) {163             e.printStackTrace();164           }165         }166         if (randomAccessFile != null) {167           try {168             randomAccessFile.close();169           } catch (IOException e) {170             e.printStackTrace();171           }172         }173 174       }175 176     }177   }178 }

数据库帮助类:

 1 package com.example.db; 2  3 import android.content.Context; 4 import android.database.sqlite.SQLiteDatabase; 5 import android.database.sqlite.SQLiteOpenHelper; 6  7 public class DBHelper extends SQLiteOpenHelper { 8   public static final String DBNAME = "download.db"; 9   public static final int VERSION = 1;10   public static final String TABLE="threadinfo";11   public static final String CREATE_DB = "create table threadinfo (_id integer primary key autoincrement,thread_id integer,url text,start integer,end integer,finished integer) ";12   public static final String DROP_DB = "drop table if exists threadinfo";13 14   public DBHelper(Context context) {15     super(context, DBNAME, null, VERSION);16   }17 18   @Override19   public void onCreate(SQLiteDatabase db) {20     db.execSQL(CREATE_DB);21 22   }23 24   @Override25   public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {26     db.execSQL(DROP_DB);27     db.execSQL(CREATE_DB);28   }29 30 }

数据库表接口类:

 1 package com.example.dao; 2  3 import java.util.List; 4  5 import com.example.entity.ThreadInfo; 6  7 public interface ThreadDAO { 8   // 新增一条线程信息 9   public void insertThread(ThreadInfo threadInfo);10 11   // 删除一条线程信息(多线程下载,可能一个url对应多个线程,所以需要2个条件)12   public void deleteThread(String url, int thread_id);13 14   // 修改一条线程信息15   public void updateThread(String url, int thread_id, int finished);16 17   // 查询线程有关信息(根据url查询下载该url的所有线程信息)18   public List<ThreadInfo> getThreadInfo(String url);19 20   // 判断线程是否已经存在21   public boolean isExists(String url, int thread_id);22 23 24 }

数据库表接口实现类:

 1 package com.example.dao; 2  3 import java.util.ArrayList; 4 import java.util.List; 5  6 import android.content.ContentValues; 7 import android.content.Context; 8 import android.database.Cursor; 9 import android.database.sqlite.SQLiteDatabase;10 11 import com.example.db.DBHelper;12 import com.example.entity.ThreadInfo;13 14 /**15  * ThreadDAO接口实现类16  * 17  * @author Balla_兔子18  * 19 */20 public class ThreadDAOImpl implements ThreadDAO {21 22   private DBHelper dbHelper;23 24   public ThreadDAOImpl(Context context) {25     dbHelper = new DBHelper(context);26   }27 28   @Override29   public void insertThread(ThreadInfo threadInfo) {30     SQLiteDatabase db = dbHelper.getWritableDatabase();31     ContentValues values = new ContentValues();32     values.put("thread_id", threadInfo.getThread_id());33     values.put("url ", threadInfo.getUrl());34     values.put("start ", threadInfo.getStart());35     values.put("end ", threadInfo.getEnd());36     values.put("finished ", threadInfo.getFinished());37     db.insert(DBHelper.TABLE, null, values);38     db.close();39   }40 41   @Override42   public void deleteThread(String url, int thread_id) {43     SQLiteDatabase db = dbHelper.getWritableDatabase();44     db.delete(DBHelper.TABLE, "url=? and thread_id=?", new String[] { url, String.valueOf(thread_id) });45     db.close();46   }47 48   @Override49   public void updateThread(String url, int thread_id, int finished) {50     SQLiteDatabase db = dbHelper.getWritableDatabase();51     db.execSQL("update threadinfo set finished = ? where url = ? and thread_id=?", new Object[] { finished, url, thread_id });52     db.close();53   }54 55   @Override56   public List<ThreadInfo> getThreadInfo(String url) {57     List<ThreadInfo> list = new ArrayList<ThreadInfo>();58     SQLiteDatabase db = dbHelper.getWritableDatabase();59     Cursor cursor = db.query(DBHelper.TABLE, null, "url=?", new String[] { url }, null, null, null);60     while (cursor.moveToNext()) {61       ThreadInfo threadInfo = new ThreadInfo();62       threadInfo.setThread_id(cursor.getInt(cursor.getColumnIndex("thread_id")));63       threadInfo.setUrl(cursor.getString(cursor.getColumnIndex("url")));64       threadInfo.setStart(cursor.getInt(cursor.getColumnIndex("start")));65       threadInfo.setEnd(cursor.getInt(cursor.getColumnIndex("end")));66       threadInfo.setFinished(cursor.getInt(cursor.getColumnIndex("finished")));67       list.add(threadInfo);68     }69     cursor.close();70     db.close();71     return list;72   }73 74   @Override75   public boolean isExists(String url, int thread_id) {76     SQLiteDatabase db = dbHelper.getWritableDatabase();77     Cursor cursor = db.query(DBHelper.TABLE, null, "url=? and thread_id=?", new String[] { url, String.valueOf(thread_id) }, null, null, null);78     boolean isExists = cursor.moveToNext();79     db.close();80     return isExists;81   }82 83 }

实体类:(文件,线程)

 1 package com.example.entity; 2  3 import java.io.Serializable; 4  5 public class FileInfo implements Serializable { 6  7   private int id; 8   private String fileName; 9   private String url;10   private int length;11   private int finished;12 13   public FileInfo() {14   }15 16   public FileInfo(int id, String fileName, String url, int length,17       int finished) {18     super();19     this.id = id;20     this.fileName = fileName;21     this.url = url;22     this.length = length;23     this.finished = finished;24   }25 26   public int getId() {27     return id;28   }29 30   public void setId(int id) {31     this.id = id;32   }33 34   public String getFileName() {35     return fileName;36   }37 38   public void setFileName(String fileName) {39     this.fileName = fileName;40   }41 42   public String getUrl() {43     return url;44   }45 46   public void setUrl(String url) {47     this.url = url;48   }49 50   public int getLength() {51     return length;52   }53 54   public void setLength(int length) {55     this.length = length;56   }57 58   public int getFinished() {59     return finished;60   }61 62   public void setFinished(int finished) {63     this.finished = finished;64   }65 66   @Override67   public String toString() {68     return "FileInfo [id=" + id + ", fileName=" + fileName + ", url=" + url69         + ", length=" + length + ", finished=" + finished + "]";70   }71 72 }

 1 package com.example.entity; 2  3 import java.io.Serializable; 4  5 public class ThreadInfo implements Serializable { 6  7   private int thread_id; 8   private String url; 9   private int start;10   private int end;11   private int finished;12 13   public ThreadInfo() {14   }15 16   public ThreadInfo(int thread_id, String url, int start, int end, int finished) {17     super();18     this.thread_id = thread_id;19     this.url = url;20     this.start = start;21     this.end = end;22     this.finished = finished;23   }24 25   public int getThread_id() {26     return thread_id;27   }28 29   public void setThread_id(int thread_id) {30     this.thread_id = thread_id;31   }32 33   public String getUrl() {34     return url;35   }36 37   public void setUrl(String url) {38     this.url = url;39   }40 41   public int getStart() {42     return start;43   }44 45   public void setStart(int start) {46     this.start = start;47   }48 49   public int getEnd() {50     return end;51   }52 53   public void setEnd(int end) {54     this.end = end;55   }56 57   public int getFinished() {58     return finished;59   }60 61   public void setFinished(int finished) {62     this.finished = finished;63   }64 65   @Override66   public String toString() {67     return "ThreadInfo [thread_id=" + thread_id + ", url=" + url + ", start=" + start + ", end=" + end + ", finished=" + finished + "]";68   }69 70 }

 

关于多线程的断点续传,其实原理差不多,还是一样把一个文件分成不同区域,然后每个区域各用一条线程去执行下载任务,然后再把文件合并,改天有时间再上个Demo给大家看吧。

 

 

作者:Balla_兔子
出处:http://www.cnblogs.com/lichenwei/
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正在看本人博客的这位童鞋,我看你气度不凡,谈吐间隐隐有王者之气,日后必有一番作为!旁边有“推荐”二字,你就顺手把它点了吧,相得准,我分文不收;相不准,你也好回来找我!