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Android实现断点下载的方法

jerry Android 2016年03月10日 收藏

最近做的项目中需要实现断点下载，即用户一次下载可以分多次进行，下载过程可以中断，在目前大多数的带离线缓存的软件都是需要实现这一功能。本文阐述了通过sqlite3简单实现了一个具有断点下载功能的demo。言归正传，开始正文。

设计

数据库表存储元数据
DBHelper.java
用于业务存储的Dao
Dao.java
抽象下载信息的Bean
LoadInfo.java
呈现下载信息View
MainActivity.java
存储下载信息Bean
DownloadInfo.java
封装好的下载类
Downloader.java

代码结构

具体实现

下载信息类：DownloadInfo.java

这里的代码很简单，就是一个用来保存下载信息的类，很简单，没啥好说的，具体看注释

  1. package entity;
  2. public class DownloadInfo {
  3.  
  4.   private int threadId;//线程ID
  5.  
  6.   private int startPos;//下载起始位置
  7.  
  8.   private int endPos;//下载结束位置
  9.  
  10.   private int completeSize;//下载完成量
  11.  
  12.   private String url;//资源URL
  13.  
  14.   public DownloadInfo(int tId,int sp, int ep,int cSize,String address){
  15.     threadId=tId;
  16.     startPos=sp;
  17.     endPos=ep;
  18.     completeSize = cSize;
  19.     url=address;
  20.   }
  21.  
  22.   /**
  23.    * @return the threadId
  24.    */
  25.   public int getThreadId() {
  26.     return threadId;
  27.   }
  28.  
  29.   /**
  30.    * @param threadId the threadId to set
  31.    */
  32.   public void setThreadId(int threadId) {
  33.     this.threadId = threadId;
  34.   }
  35.  
  36.   /**
  37.    * @return the startPos
  38.    */
  39.   public int getStartPos() {
  40.     return startPos;
  41.   }
  42.  
  43.   /**
  44.    * @param startPos the startPos to set
  45.    */
  46.   public void setStartPos(int startPos) {
  47.     this.startPos = startPos;
  48.   }
  49.  
  50.   /**
  51.    * @return the endPos
  52.    */
  53.   public int getEndPos() {
  54.     return endPos;
  55.   }
  56.  
  57.   /**
  58.    * @param endPos the endPos to set
  59.    */
  60.   public void setEndPos(int endPos) {
  61.     this.endPos = endPos;
  62.   }
  63.  
  64.   /**
  65.    * @return the completeSize
  66.    */
  67.   public int getCompleteSize() {
  68.     return completeSize;
  69.   }
  70.  
  71.   /**
  72.    * @param completeSize the completeSize to set
  73.    */
  74.   public void setCompleteSize(int completeSize) {
  75.     this.completeSize = completeSize;
  76.   }
  77.  
  78.   /**
  79.    * @return the url
  80.    */
  81.   public String getUrl() {
  82.     return url;
  83.   }
  84.  
  85.   /**
  86.    * @param url the url to set
  87.    */
  88.   public void setUrl(String url) {
  89.     this.url = url;
  90.   }
  91.  
  92.   @Override
  93.   public String toString() {
  94.     // TODO Auto-generated method stub
  95.     return "threadId:"+threadId+",startPos:"+startPos+",endPos："+endPos+",completeSize:"+completeSize+",url:"+url;
  96.   }
  97. }
  98.  

数据库 DBHelper.java

  1. package 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.  
  9.   String sql ="create table download_info (id integer PRIMARY KEY AUTOINCREMENT,"
  10.       + "thread_id integer,"
  11.       + "start_pos integer,"
  12.       + "end_pos integer,"
  13.       + "complete_size integer,"
  14.       + "url char)";
  15.  
  16.   public DBHelper(Context context) {
  17.     // TODO Auto-generated constructor stub
  18.     super(context, "download.db", null, 1);
  19.   }
  20.  
  21.   @Override
  22.   public void onCreate(SQLiteDatabase db) {
  23.     // TODO Auto-generated method stub
  24.     db.execSQL(sql);
  25.   }
  26.  
  27.   @Override
  28.   public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
  29.     // TODO Auto-generated method stub
  30.  
  31.   }
  32.  
  33. }
  34.  

数据库业务管理类 Dao.java

  1. package db;
  2.  
  3. import java.util.ArrayList;
  4. import java.util.List;
  5.  
  6. import android.content.Context;
  7. import android.database.Cursor;
  8. import android.database.sqlite.SQLiteDatabase;
  9. import entity.DownloadInfo;
  10.  
  11. public class Dao {
  12.  
  13.   private DBHelper dbHelper;
  14.  
  15.   public Dao(Context context){
  16.     dbHelper = new DBHelper(context);
  17.   }
  18.  
  19.   public boolean isNewTask(String url){
  20.     SQLiteDatabase db = dbHelper.getReadableDatabase();
  21.     String sql = "select count(*) from download_info where url=?";
  22.     Cursor cursor = db.rawQuery(sql, new String[]{url});
  23.     cursor.moveToFirst();
  24.     int count = cursor.getInt(0);
  25.     cursor.close();
  26.     return count == 0;
  27.   }
  28.  
  29.   public void saveInfo(List<DownloadInfo> infos){
  30.     SQLiteDatabase db = dbHelper.getWritableDatabase();
  31.     String sql = "insert into download_info(thread_id,start_pos,end_pos,complete_size,url) values(?,?,?,?,?)";
  32.     Object[] bindArgs= null;
  33.     for(DownloadInfo info:infos){
  34.       bindArgs=new Object[]{info.getThreadId(),info.getStartPos(),info.getEndPos(),info.getCompleteSize(),info.getUrl()};
  35.       db.execSQL(sql, bindArgs);
  36.     }
  37.  
  38.   }
  39.   public List<DownloadInfo> getInfo(String url){
  40.     SQLiteDatabase db = dbHelper.getReadableDatabase();
  41.     List<DownloadInfo> infos = new ArrayList<DownloadInfo>();
  42.     String sql ="select thread_id,start_pos,end_pos,complete_size,url from download_info where url=?";
  43.     Cursor cursor=db.rawQuery(sql, new String[]{url});
  44.     while(cursor.moveToNext()){
  45.       DownloadInfo info = new DownloadInfo(cursor.getInt(0), cursor.getInt(1), cursor.getInt(2), cursor.getInt(3),cursor.getString(4));
  46.       infos.add(info);
  47.     }
  48.     cursor.close();
  49.     return infos;
  50.  
  51.   }
  52.  
  53.   public void deleteInfo(String url){
  54.     SQLiteDatabase db = dbHelper.getWritableDatabase();
  55.     db.delete("download_info", "url=?", new String[]{url});
  56.     db.close();
  57.   }
  58.  
  59.   public void updateInfo(int completeSize,int threadId,String url){
  60.     SQLiteDatabase db = dbHelper.getWritableDatabase();
  61.     String sql ="update download_info set complete_size=? where thread_id=? and url=?";
  62.     db.execSQL(sql, new Object[]{completeSize,threadId,url});
  63.   }
  64.  
  65.   public void closeDB(){
  66.     dbHelper.close();
  67.   }
  68.  
  69. }
  70.  

当前状态保存类 LoadInfo.java

  1. package entity;
  2.  
  3. public class LoadInfo {
  4.   private int fileSize;
  5.   private int completeSize;  
  6.   private String url;
  7.   public LoadInfo(int fs,int cSize,String address){    
  8.     fileSize=fs;    
  9.     completeSize = cSize;      
  10.     url=address;
  11.   }  
  12.   /**
  13.    * @return the fileSize
  14.    */
  15.   public int getFileSize() {
  16.     return fileSize;
  17.   }
  18.   /**
  19.    * @param fileSize the fileSize to set
  20.    */
  21.   public void setFileSize(int fileSize) {
  22.     this.fileSize = fileSize;
  23.   }
  24.   /**
  25.    * @return the completeSize
  26.    */
  27.   public int getCompleteSize() {
  28.     return completeSize;
  29.   }
  30.  
  31.   /**
  32.    * @param completeSize the completeSize to set
  33.    */
  34.   public void setCompleteSize(int completeSize) {
  35.     this.completeSize = completeSize;
  36.   }
  37.  
  38.   /**
  39.    * @return the url
  40.    */
  41.   public String getUrl() {
  42.     return url;
  43.   }
  44.  
  45.   /**
  46.    * @param url the url to set
  47.    */
  48.   public void setUrl(String url) {
  49.     this.url = url;
  50.   }
  51. }
  52.  

下载助手类：Downloader.java

  1. package com.winton.downloadmanager;
  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.ArrayList;
  11. import java.util.List;
  12.  
  13. import android.content.Context;
  14. import android.os.Handler;
  15. import android.os.Message;
  16. import db.Dao;
  17. import entity.DownloadInfo;
  18. import entity.LoadInfo;
  19.  
  20. public class Downloader {
  21.   private String url;
  22.   private String localPath;
  23.   private int threadCount;
  24.   private Handler mHanler;
  25.   private Dao dao;
  26.   private int fileSize;
  27.  
  28.   private List<DownloadInfo> infos;
  29.  
  30.   private final static int INIT = 1;
  31.  
  32.   private final static int DOWNLOADING =2;
  33.  
  34.   private final static int PAUSE =3;
  35.  
  36.   private int state = INIT;
  37.  
  38.   public Downloader(String address,String lPath,int thCount,Context context,Handler handler){
  39.     url =address;
  40.     localPath = lPath;
  41.     threadCount = thCount;
  42.     mHanler = handler;
  43.     dao = new Dao(context);
  44.   }
  45.  
  46.   public boolean isDownloading(){
  47.     return state == DOWNLOADING;
  48.   }
  49.  
  50.   public LoadInfo getDownLoadInfos(){
  51.     if(isFirstDownload(url)){
  52.       init();
  53.       int range = fileSize/threadCount;
  54.       infos = new ArrayList<DownloadInfo>();
  55.       for(int i=0;i<=threadCount-1;i++){
  56.         DownloadInfo info = new DownloadInfo(i, i*range, (i+1)*range-1, 0, url);
  57.         infos.add(info);
  58.       }
  59.       dao.saveInfo(infos);
  60.       return new LoadInfo(fileSize, 0, url);
  61.     }else{
  62.       infos = dao.getInfo(url);
  63.       int size = 0;
  64.       int completeSize =0;
  65.       for(DownloadInfo info:infos){
  66.         completeSize += info.getCompleteSize();
  67.         size += info.getEndPos()-info.getStartPos()+1;
  68.       }
  69.       return new LoadInfo(size, completeSize, url);
  70.     }
  71.   }
  72.   public boolean isFirstDownload(String url){
  73.     return dao.isNewTask(url);
  74.   }
  75.  
  76.   public void init(){
  77.     try {
  78.       URL mUrl = new URL(this.url);
  79.       HttpURLConnection connection = (HttpURLConnection)mUrl.openConnection();
  80.       connection.setConnectTimeout(5000);
  81.       connection.setRequestMethod("GET");
  82.       fileSize = connection.getContentLength();
  83.  
  84.       File file = new File(localPath);
  85.       if(!file.exists()){
  86.         file.createNewFile();
  87.       }
  88.       RandomAccessFile accessFile = new RandomAccessFile(file, "rwd");
  89.       accessFile.setLength(fileSize);
  90.       accessFile.close();
  91.       connection.disconnect();
  92.  
  93.     } catch (MalformedURLException e) {
  94.       // TODO Auto-generated catch block
  95.       e.printStackTrace();
  96.     } catch (IOException e) {
  97.       // TODO Auto-generated catch block
  98.       e.printStackTrace();
  99.     } 
  100.   }
  101.  
  102.   public void download(){
  103.     if(infos != null){
  104.       if(state ==DOWNLOADING){
  105.         return;
  106.       }
  107.       state = DOWNLOADING;
  108.       for(DownloadInfo info:infos){
  109.         new DownloadThread(info.getThreadId(), info.getStartPos(), info.getEndPos(), info.getCompleteSize(), info.getUrl()).start();
  110.  
  111.       }
  112.     }
  113.   }
  114.  
  115.   class DownloadThread extends Thread{
  116.  
  117.     private int threadId;
  118.     private int startPos;
  119.     private int endPos;
  120.     private int completeSize;
  121.     private String url;
  122.  
  123.     public DownloadThread(int tId,int sp,int ep,int cSize,String address) {
  124.       // TODO Auto-generated constructor stub
  125.       threadId=tId;
  126.       startPos=sp;
  127.       endPos = ep;
  128.       completeSize = cSize;
  129.       url = address;
  130.     }
  131.  
  132.     @Override
  133.     public void run() {
  134.       // TODO Auto-generated method stub
  135.       HttpURLConnection connection = null;
  136.       RandomAccessFile randomAccessFile = null;
  137.       InputStream is = null;
  138.  
  139.       try {
  140.         URL mUrl = new URL(url);
  141.         connection = (HttpURLConnection)mUrl.openConnection();
  142.         connection.setConnectTimeout(5000);
  143.         connection.setRequestMethod("GET");
  144.         connection.setRequestProperty("Range", "bytes="+(startPos+completeSize)+"-"+endPos);
  145.         randomAccessFile = new RandomAccessFile(localPath, "rwd");
  146.         randomAccessFile.seek(startPos+completeSize);
  147.         is=connection.getInputStream();
  148.         byte[] buffer = new byte[4096];
  149.         int length =-1;
  150.         while((length=is.read(buffer)) != -1){
  151.           randomAccessFile.write(buffer, 0, length);
  152.           completeSize +=length;
  153.           dao.updateInfo(threadId, completeSize, url);
  154.           Message msg = Message.obtain();
  155.           msg.what=1;
  156.           msg.obj=url;
  157.           msg.arg1=length;
  158.           mHanler.sendMessage(msg);
  159.           if(state==PAUSE){
  160.             return;
  161.           }
  162.         }
  163.       } catch (MalformedURLException e) {
  164.         // TODO Auto-generated catch block
  165.         e.printStackTrace();
  166.       } catch (IOException e) {
  167.         // TODO Auto-generated catch block
  168.         e.printStackTrace();
  169.       }finally{
  170.         try {
  171.           is.close();
  172.           randomAccessFile.close();
  173.           connection.disconnect();
  174.           dao.closeDB();
  175.         } catch (IOException e) {
  176.           // TODO Auto-generated catch block
  177.           e.printStackTrace();
  178.         }
  179.  
  180.       }
  181.  
  182.     }
  183.  
  184.   }
  185.   public void delete(String url){
  186.     dao.deleteInfo(url);
  187.   }
  188.   public void reset(){
  189.     state=INIT;
  190.   }
  191.   public void pause(){
  192.     state=PAUSE;
  193.   }
  194.  
  195. }
  196.  

View呈现类：MainActivity.java

  1. package com.winton.downloadmanager;
  2.  
  3. import android.app.Activity;
  4. import android.os.Bundle;
  5. import android.os.Environment;
  6. import android.os.Handler;
  7. import android.os.Message;
  8. import android.view.View;
  9. import android.view.View.OnClickListener;
  10. import android.widget.Button;
  11. import android.widget.ProgressBar;
  12. import android.widget.TextView;
  13. import android.widget.Toast;
  14. import entity.LoadInfo;
  15.  
  16. public class MainActivity extends Activity implements OnClickListener{
  17.   private TextView name;
  18.  
  19.   private ProgressBar process;
  20.  
  21.   private Button start,stop;
  22.   private Downloader downloader;
  23.  
  24.   //处理下载进度UI的
  25.   Handler handler = new Handler(){
  26.     public void handleMessage(android.os.Message msg) {
  27.       if(msg.what==1){
  28.         name.setText((String)msg.obj);
  29.         int lenght = msg.arg1;
  30.         process.incrementProgressBy(lenght);
  31.       }
  32.       if(msg.what==2){
  33.         int max =msg.arg1;
  34.         process.setMax(max);
  35.         Toast.makeText(getApplicationContext(), max+"", 1).show();
  36.       }
  37.     };
  38.   };
  39.   @Override
  40.   protected void onCreate(Bundle savedInstanceState) {
  41.     super.onCreate(savedInstanceState);
  42.     setContentView(R.layout.activity_main);
  43.     name=(TextView)findViewById(R.id.tv_name);
  44.     process=(ProgressBar)findViewById(R.id.pb_download);
  45.     start = (Button)findViewById(R.id.bt_start);
  46.     stop = (Button)findViewById(R.id.bt_stop);
  47.     start.setOnClickListener(this);
  48.     stop.setOnClickListener(this);
  49.     downloader=new Downloader("http://img4.duitang.com/uploads/item/201206/11/20120611174542_5KRMj.jpeg", Environment.getExternalStorageDirectory().getPath()+"/test1.jpg", 1, getApplicationContext(), handler);
  50.   }
  51.  
  52.   @Override
  53.   public void onClick(View v) {
  54.     // TODO Auto-generated method stub
  55.     if(v==start){
  56.       new Thread(new Runnable() {
  57.  
  58.         @Override
  59.         public void run() {
  60.           // TODO Auto-generated method stub
  61.           LoadInfo loadInfo = downloader.getDownLoadInfos();
  62.           Message msg =handler.obtainMessage();
  63.           msg.what=2;
  64.           msg.arg1=loadInfo.getFileSize();
  65.           handler.sendMessage(msg);
  66.           downloader.download();
  67.         }
  68.       }).start();
  69.       return;
  70.     }
  71.     if(v==stop){
  72.       downloader.pause();
  73.       return;
  74.     }
  75.   }  
  76. }
  77.  

运行效果

总体比较简单，基本实现了 断点下载的功能，而且开启了多个线程去实现分块下载，对初学的同学有一定的帮助。

这些代码我也是从网上各种搜集而来，自己亲自动手敲了一遍，并做了一些小的改动，对整个断点下载的过程有了一个深刻的认识。因此平时要多敲代码，善于总结，必能有所收获。

android断点下载
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