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今天跟大家一起分享下android开发中比较难的一个环节,可能很多人看到这个标题就会感觉头很大,的确如果没有良好的编码能力和逻辑思维,这块是很难搞明白的,前面2次总结中已经为大家分享过有关技术的一些基本要领,我们先一起简单回顾下它的基本原理。

  android 多线程断点续传下载 一

  android 多线程断点续传下载 二

什么是多线程下载？

多线程下载其实就是迅雷,BT一些下载原理,通过多个线程同时和服务器连接,那么你就可以榨取到较高的带宽了,大致做法是将文件切割成N块,每块交给单独一个线程去下载,各自下载完成后将文件块组合成一个文件,程序上要完成做切割和组装的小算法

什么是断点续传?

断点续传,就是当我们下载未结束时候,退出保存下载进度,当下次打开继续下载的时接着上次的进度继续下载,不用每次下载都重新开始,那么有关断点续传的原理和实现手段,可参考我以前的一篇总结 里面详细讲解http协议断点续传的原理,务必要看懂,否则你无法真正理解本节代码

怎么完成多线程断点续传?

将两者合二为一需要程序记住每个文件块的下载进度,并保存入库,当下载程序启动时候你需要判断程序是否已经下载过该文件,并取出各个文件块的保存记录,换算出下载进度继续下载,在这里你需要掌握java多线程的基本知识,handler的使用,以及集合,算法,文件操作等基本技能,同时还要解决sqlite数据库的同步问题,因为它是不太怎么支持多线程操作的,控制不好经常会出现库被锁定的异常,同时在android2.3以后就不能activity中直接操作http,否则你将收到系统送上的NetworkOnMainThreadException异常,在UI体验上一定记住要使用异步完成,既然大致思路已经清楚,下面我们开始分析程序:

package cn.demo.DBHelper;  import android.content.Context;import android.database.sqlite.SQLiteDatabase;import android.database.sqlite.SQLiteOpenHelper;      /**      * 建立一个数据库帮助类      */ public class DBHelper extends SQLiteOpenHelper {     //download.db-->数据库名     public DBHelper(Context context) {         super(context, "download.db", null, 1);     }          /**      * 在download.db数据库下创建一个download_info表存储下载信息      */     @Override     public void onCreate(SQLiteDatabase db) {         db.execSQL("create table download_info(_id integer PRIMARY KEY AUTOINCREMENT, thread_id integer, "                 + "start_pos integer, end_pos integer, compelete_size integer,url char)");     }     @Override     public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {      }  }

 

 数据库操作要借助单例和同步,来保证线程的执行顺序,以免多个线程争相抢用sqlite资源导致异常出现

package cn.demo.Dao;import java.util.ArrayList;import java.util.List;import android.content.Context;import android.database.Cursor;import android.database.sqlite.SQLiteDatabase;import cn.demo.DBHelper.DBHelper;import cn.demo.entity.DownloadInfo;/** *  * 一个业务类 */public class Dao {  	private static Dao dao=null;	private Context context; 	private  Dao(Context context) { 		this.context=context;	}	public static  Dao getInstance(Context context){		if(dao==null){			dao=new Dao(context); 		}		return dao;	}	public  SQLiteDatabase getConnection() {		SQLiteDatabase sqliteDatabase = null;		try { 			sqliteDatabase= new DBHelper(context).getReadableDatabase();		} catch (Exception e) {  		}		return sqliteDatabase;	}	/**	 * 查看数据库中是否有数据	 */	public synchronized boolean isHasInfors(String urlstr) {		SQLiteDatabase database = getConnection();		int count = -1;		Cursor cursor = null;		try {			String sql = "select count(*)  from download_info where url=?";			cursor = database.rawQuery(sql, new String[] { urlstr });			if (cursor.moveToFirst()) {				count = cursor.getInt(0);			} 		} catch (Exception e) {			e.printStackTrace();		} finally {			if (null != database) {				database.close();			}			if (null != cursor) {				cursor.close();			}		}		return count == 0;	}	/**	 * 保存 下载的具体信息	 */	public synchronized void saveInfos(List
   
     infos) {		SQLiteDatabase database = getConnection();		try {			for (DownloadInfo info : infos) {				String sql = "insert into download_info(thread_id,start_pos, end_pos,compelete_size,url) values (?,?,?,?,?)";				Object[] bindArgs = { info.getThreadId(), info.getStartPos(),						info.getEndPos(), info.getCompeleteSize(),						info.getUrl() };				database.execSQL(sql, bindArgs);			}		} catch (Exception e) {			e.printStackTrace();		} finally {			if (null != database) {				database.close();			}		}	}	/**	 * 得到下载具体信息	 */	public synchronized List
    
      getInfos(String urlstr) {		List
     
       list = new ArrayList
      
       ();		SQLiteDatabase database = getConnection();		Cursor cursor = null;		try {			String sql = "select thread_id, start_pos, end_pos,compelete_size,url from download_info where url=?";			cursor = database.rawQuery(sql, new String[] { urlstr });			while (cursor.moveToNext()) {				DownloadInfo info = new DownloadInfo(cursor.getInt(0),						cursor.getInt(1), cursor.getInt(2), cursor.getInt(3),						cursor.getString(4));				list.add(info);			}		} catch (Exception e) {			e.printStackTrace();		} finally {			if (null != database) {				database.close();			}			if (null != cursor) {				cursor.close();			}		}		return list;	}	/**	 * 更新数据库中的下载信息	 */	public synchronized void updataInfos(int threadId, int compeleteSize, String urlstr) {		SQLiteDatabase database = getConnection();		try {			String sql = "update download_info set compelete_size=? where thread_id=? and url=?";			Object[] bindArgs = { compeleteSize, threadId, urlstr };			database.execSQL(sql, bindArgs);		} catch (Exception e) {			e.printStackTrace();		} finally {			if (null != database) {				database.close();			}		}	}	/**	 * 下载完成后删除数据库中的数据	 */	public synchronized void delete(String url) {		SQLiteDatabase database = getConnection();		try {			database.delete("download_info", "url=?", new String[] { url });		} catch (Exception e) {			e.printStackTrace();		} finally {			if (null != database) {				database.close();			}		}	}}
      
     
    
   

 

package cn.demo.download;import java.util.List;import java.util.Map;import android.content.Context;import android.view.LayoutInflater;import android.view.View;import android.view.View.OnClickListener;import android.view.ViewGroup;import android.widget.BaseAdapter;import android.widget.Button;import android.widget.TextView;public class DownLoadAdapter extends BaseAdapter{	 	private LayoutInflater mInflater;	private List

注意子线程不要影响主UI线程,灵活运用task和handler,各取所长,保证用户体验,handler通常在主线程中有利于专门负责处理UI的一些工作

package cn.demo.download;  import java.util.ArrayList;import java.util.HashMap;import java.util.List;import java.util.Map;import android.app.ListActivity;import android.os.AsyncTask;import android.os.Bundle;import android.os.Handler;import android.os.Message;import android.view.View;import android.widget.Button;import android.widget.LinearLayout;import android.widget.LinearLayout.LayoutParams;import android.widget.ProgressBar; import android.widget.TextView;import android.widget.Toast;import cn.demo.entity.LoadInfo;import cn.demo.service.Downloader; public class MainActivity extends ListActivity {      // 固定下载的资源路径，这里可以设置网络上的地址     private static final String URL = "http://download.haozip.com/";     // 固定存放下载的音乐的路径：SD卡目录下     private static final String SD_PATH = "/mnt/sdcard/";     // 存放各个下载器     private Map
   
     downloaders = new HashMap
    
     ();     // 存放与下载器对应的进度条     private Map
     
       ProgressBars = new HashMap
      
       ();     /**      * 利用消息处理机制适时更新进度条      */     private Handler mHandler = new Handler() {         public void handleMessage(Message msg) {             if (msg.what == 1) {                 String url = (String) msg.obj;                 int length = msg.arg1;                 ProgressBar bar = ProgressBars.get(url);                 if (bar != null) {                     // 设置进度条按读取的length长度更新                     bar.incrementProgressBy(length);                     if (bar.getProgress() == bar.getMax()) {                    	 LinearLayout layout = (LinearLayout) bar.getParent();                    	 TextView resouceName=(TextView)layout.findViewById(R.id.tv_resouce_name);                         Toast.makeText(MainActivity.this, "["+resouceName.getText()+"]下载完成！", Toast.LENGTH_SHORT).show();                         // 下载完成后清除进度条并将map中的数据清空                         layout.removeView(bar);                         ProgressBars.remove(url);                         downloaders.get(url).delete(url);                         downloaders.get(url).reset();                         downloaders.remove(url);                                                  Button btn_start=(Button)layout.findViewById(R.id.btn_start);                         Button btn_pause=(Button)layout.findViewById(R.id.btn_pause);                         btn_pause.setVisibility(View.GONE);                         btn_start.setVisibility(View.GONE);                     }                 }             }         }     };     @Override     public void onCreate(Bundle savedInstanceState) {         super.onCreate(savedInstanceState);         setContentView(R.layout.main);          showListView();     }     // 显示listView，这里可以随便添加     private void showListView() {         List
       
      
     
    
   

 

 这是一个信息的实体,记录了一些字典信息,可以认为是一个简单bean对象

package cn.demo.entity; /**  *创建一个下载信息的实体类  */ public class DownloadInfo {     private int threadId;//下载器id     private int startPos;//开始点     private int endPos;//结束点     private int compeleteSize;//完成度     private String url;//下载器网络标识     public DownloadInfo(int threadId, int startPos, int endPos,             int compeleteSize,String url) {         this.threadId = threadId;         this.startPos = startPos;         this.endPos = endPos;         this.compeleteSize = compeleteSize;         this.url=url;     }     public DownloadInfo() {     }     public String getUrl() {         return url;     }     public void setUrl(String url) {         this.url = url;     }     public int getThreadId() {         return threadId;     }     public void setThreadId(int threadId) {         this.threadId = threadId;     }     public int getStartPos() {         return startPos;     }     public void setStartPos(int startPos) {         this.startPos = startPos;     }     public int getEndPos() {         return endPos;     }     public void setEndPos(int endPos) {         this.endPos = endPos;     }     public int getCompeleteSize() {         return compeleteSize;     }     public void setCompeleteSize(int compeleteSize) {         this.compeleteSize = compeleteSize;     }      @Override     public String toString() {         return "DownloadInfo [threadId=" + threadId                 + ", startPos=" + startPos + ", endPos=" + endPos                 + ", compeleteSize=" + compeleteSize +"]";     } }

package cn.demo.entity; /**  *自定义的一个记载下载器详细信息的类   */ public class LoadInfo {     public int fileSize;//文件大小     private int complete;//完成度     private String urlstring;//下载器标识     public LoadInfo(int fileSize, int complete, String urlstring) {         this.fileSize = fileSize;         this.complete = complete;         this.urlstring = urlstring;     }     public LoadInfo() {     }     public int getFileSize() {         return fileSize;     }     public void setFileSize(int fileSize) {         this.fileSize = fileSize;     }     public int getComplete() {         return complete;     }     public void setComplete(int complete) {         this.complete = complete;     }     public String getUrlstring() {         return urlstring;     }     public void setUrlstring(String urlstring) {         this.urlstring = urlstring;     }     @Override     public String toString() {         return "LoadInfo [fileSize=" + fileSize + ", complete=" + complete                 + ", urlstring=" + urlstring + "]";     } }

 

这是一个核心类,专门用来处理下载的

package cn.demo.service;  import java.io.File;import java.io.InputStream;import java.io.RandomAccessFile;import java.net.HttpURLConnection;import java.net.URL;import java.util.ArrayList;import java.util.List;import android.content.Context;import android.os.AsyncTask;import android.os.Handler;import android.os.Message;import android.util.Log;import cn.demo.Dao.Dao;import cn.demo.entity.DownloadInfo;import cn.demo.entity.LoadInfo;  public class Downloader {     private String urlstr;// 下载的地址     private String localfile;// 保存路径     private int threadcount;// 线程数     private Handler mHandler;// 消息处理器      private int fileSize;// 所要下载的文件的大小     private Context context;      private List
   
     infos;// 存放下载信息类的集合     private static final int INIT = 1;//定义三种下载的状态：初始化状态，正在下载状态，暂停状态     private static final int DOWNLOADING = 2;     private static final int PAUSE = 3;     private int state = INIT;      public Downloader(String urlstr, String localfile, int threadcount,             Context context, Handler mHandler) {         this.urlstr = urlstr;         this.localfile = localfile;         this.threadcount = threadcount;         this.mHandler = mHandler;         this.context = context;     }     /**      *判断是否正在下载       */     public boolean isdownloading() {         return state == DOWNLOADING;     }     /**      * 得到downloader里的信息      * 首先进行判断是否是第一次下载，如果是第一次就要进行初始化，并将下载器的信息保存到数据库中      * 如果不是第一次下载，那就要从数据库中读出之前下载的信息（起始位置，结束为止，文件大小等），并将下载信息返回给下载器      */     public LoadInfo getDownloaderInfors() {         if (isFirst(urlstr)) {             Log.v("TAG", "isFirst");             init();             int range = fileSize / threadcount;             infos = new ArrayList
    
     ();             for (int i = 0; i < threadcount - 1; i++) {                 DownloadInfo info = new DownloadInfo(i, i * range, (i + 1)* range - 1, 0, urlstr);                 infos.add(info);             }             DownloadInfo info = new DownloadInfo(threadcount - 1,(threadcount - 1) * range, fileSize - 1, 0, urlstr);             infos.add(info);             //保存infos中的数据到数据库             Dao.getInstance(context).saveInfos(infos);             //创建一个LoadInfo对象记载下载器的具体信息             LoadInfo loadInfo = new LoadInfo(fileSize, 0, urlstr);             return loadInfo;         } else {             //得到数据库中已有的urlstr的下载器的具体信息             infos = Dao.getInstance(context).getInfos(urlstr);             Log.v("TAG", "not isFirst size=" + infos.size());             int size = 0;             int compeleteSize = 0;             for (DownloadInfo info : infos) {                 compeleteSize += info.getCompeleteSize();                 size += info.getEndPos() - info.getStartPos() + 1;             }             return new LoadInfo(size, compeleteSize, urlstr);         }     }      /**      * 初始化      */     private void init() {         try {             URL url = new URL(urlstr);             HttpURLConnection connection = (HttpURLConnection) url.openConnection();             connection.setConnectTimeout(5000);             connection.setRequestMethod("GET");             fileSize = connection.getContentLength();              File file = new File(localfile);             if (!file.exists()) {                 file.createNewFile();             }             // 本地访问文件             RandomAccessFile accessFile = new RandomAccessFile(file, "rwd");             accessFile.setLength(fileSize);             accessFile.close();             connection.disconnect();         } catch (Exception e) {             e.printStackTrace();         }     }       /**      * 判断是否是第一次 下载      */     private boolean isFirst(String urlstr) {         return Dao.getInstance(context).isHasInfors(urlstr);     }      /**      * 利用线程开始下载数据      */     public void download() {         if (infos != null) {             if (state == DOWNLOADING)                 return;             state = DOWNLOADING;             for (DownloadInfo info : infos) {                 new MyThread(info.getThreadId(), info.getStartPos(),                         info.getEndPos(), info.getCompeleteSize(),                         info.getUrl()).start();             }         }     }      public class MyThread extends Thread {         private int threadId;         private int startPos;         private int endPos;         private int compeleteSize;         private String urlstr;          public MyThread(int threadId, int startPos, int endPos,                 int compeleteSize, String urlstr) {             this.threadId = threadId;             this.startPos = startPos;             this.endPos = endPos;             this.compeleteSize = compeleteSize;             this.urlstr = urlstr;         }         @Override         public void run() {             HttpURLConnection connection = null;             RandomAccessFile randomAccessFile = null;             InputStream is = null;             try {                 URL url = new URL(urlstr);                 connection = (HttpURLConnection) url.openConnection();                 connection.setConnectTimeout(5000);                 connection.setRequestMethod("GET");                 // 设置范围，格式为Range：bytes x-y;                 connection.setRequestProperty("Range", "bytes="+(startPos + compeleteSize) + "-" + endPos);                  randomAccessFile = new RandomAccessFile(localfile, "rwd");                 randomAccessFile.seek(startPos + compeleteSize);                 // 将要下载的文件写到保存在保存路径下的文件中                 is = connection.getInputStream();                 byte[] buffer = new byte[4096];                 int length = -1;                 while ((length = is.read(buffer)) != -1) {                     randomAccessFile.write(buffer, 0, length);                     compeleteSize += length;                     // 更新数据库中的下载信息                     Dao.getInstance(context).updataInfos(threadId, compeleteSize, urlstr);                     // 用消息将下载信息传给进度条，对进度条进行更新                     Message message = Message.obtain();                     message.what = 1;                     message.obj = urlstr;                     message.arg1 = length;                     mHandler.sendMessage(message);                     if (state == PAUSE) {                         return;                     }                 }             } catch (Exception e) {                 e.printStackTrace();             }           }     }     //删除数据库中urlstr对应的下载器信息     public void delete(String urlstr) {    	 Dao.getInstance(context).delete(urlstr);     }     //设置暂停     public void pause() {         state = PAUSE;     }     //重置下载状态     public void reset() {         state = INIT;     } }
    
   

以下是些xml文件

 

 

运行效果如下

 

 

 

  android 多线程断点续传下载 四-模仿下载助手

 

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