Android实现断点下载的方法

概述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，

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

package entity;public class DownloadInfo {  private int threadID;//线程ID  private int startPos;//下载起始位置  private int endPos;//下载结束位置  private int completeSize;//下载完成量  private String url;//资源URL  public DownloadInfo(int tID,int sp,int ep,int cSize,String address){    threadID=tID;    startPos=sp;    endPos=ep;    completeSize = cSize;    url=address;  }  /**   * @return the threadID   */  public int getThreadID() {    return threadID;  }  /**   * @param threadID the threadID to set   */  public voID setThreadID(int threadID) {    this.threadID = threadID;  }  /**   * @return the startPos   */  public int getStartPos() {    return startPos;  }  /**   * @param startPos the startPos to set   */  public voID setStartPos(int startPos) {    this.startPos = startPos;  }  /**   * @return the endPos   */  public int getEndPos() {    return endPos;  }  /**   * @param endPos the endPos to set   */  public voID setEndPos(int endPos) {    this.endPos = endPos;  }  /**   * @return the completeSize   */  public int getCompleteSize() {    return completeSize;  }  /**   * @param completeSize the completeSize to set   */  public voID setCompleteSize(int completeSize) {    this.completeSize = completeSize;  }  /**   * @return the url   */  public String getUrl() {    return url;  }  /**   * @param url the url to set   */  public voID setUrl(String url) {    this.url = url;  }  @OverrIDe  public String toString() {    // Todo auto-generated method stub    return "threadID:"+threadID+",startPos:"+startPos+",endPos："+endPos+",completeSize:"+completeSize+",url:"+url;  }}

数据库 DBHelper.java

package db;import androID.content.Context;import androID.database.sqlite.sqliteDatabase;import androID.database.sqlite.sqliteOpenHelper;public class DBHelper extends sqliteOpenHelper {  String sql ="create table download_info (ID integer PRIMARY KEY autoINCREMENT,"      + "thread_ID integer,"      + "start_pos integer,"      + "end_pos integer,"      + "complete_size integer,"      + "url char)";  public DBHelper(Context context) {    // Todo auto-generated constructor stub    super(context,"download.db",null,1);  }  @OverrIDe  public voID onCreate(sqliteDatabase db) {    // Todo auto-generated method stub    db.execsql(sql);  }  @OverrIDe  public voID onUpgrade(sqliteDatabase db,int oldVersion,int newVersion) {    // Todo auto-generated method stub  }}

数据库业务管理类 Dao.java

package db;import java.util.ArrayList;import java.util.List;import androID.content.Context;import androID.database.Cursor;import androID.database.sqlite.sqliteDatabase;import entity.DownloadInfo;public class Dao {  private DBHelper dbHelper;  public Dao(Context context){    dbHelper = new DBHelper(context);  }  public boolean isNewTask(String url){    sqliteDatabase db = dbHelper.getReadableDatabase();    String sql = "select count(*) from download_info where url=?";    Cursor cursor = db.rawquery(sql,new String[]{url});    cursor.movetoFirst();    int count = cursor.getInt(0);    cursor.close();    return count == 0;  }  public voID saveInfo(List<DownloadInfo> infos){    sqliteDatabase db = dbHelper.getWritableDatabase();    String sql = "insert into download_info(thread_ID,start_pos,end_pos,complete_size,url) values(?,?,?)";    Object[] bindArgs= null;    for(DownloadInfo info:infos){      bindArgs=new Object[]{info.getThreadID(),info.getStartPos(),info.getEndPos(),info.getCompleteSize(),info.getUrl()};      db.execsql(sql,bindArgs);    }  }  public List<DownloadInfo> getInfo(String url){    sqliteDatabase db = dbHelper.getReadableDatabase();    List<DownloadInfo> infos = new ArrayList<DownloadInfo>();    String sql ="select thread_ID,url from download_info where url=?";    Cursor cursor=db.rawquery(sql,new String[]{url});    while(cursor.movetoNext()){      DownloadInfo info = new DownloadInfo(cursor.getInt(0),cursor.getInt(1),cursor.getInt(2),cursor.getInt(3),cursor.getString(4));      infos.add(info);    }    cursor.close();    return infos;  }  public voID deleteInfo(String url){    sqliteDatabase db = dbHelper.getWritableDatabase();    db.delete("download_info","url=?",new String[]{url});    db.close();  }  public voID updateInfo(int completeSize,int threadID,String url){    sqliteDatabase db = dbHelper.getWritableDatabase();    String sql ="update download_info set complete_size=? where thread_ID=? and url=?";    db.execsql(sql,new Object[]{completeSize,threadID,url});  }  public voID closeDB(){    dbHelper.close();  }}

当前状态保存类 LoadInfo.java

package entity;public class LoadInfo {  private int fileSize;  private int completeSize;    private String url;  public LoadInfo(int fs,String address){        fileSize=fs;        completeSize = cSize;          url=address;  }    /**   * @return the fileSize   */  public int getfileSize() {    return fileSize;  }  /**   * @param fileSize the fileSize to set   */  public voID setfileSize(int fileSize) {    this.fileSize = fileSize;  }  /**   * @return the completeSize   */  public int getCompleteSize() {    return completeSize;  }  /**   * @param completeSize the completeSize to set   */  public voID setCompleteSize(int completeSize) {    this.completeSize = completeSize;  }  /**   * @return the url   */  public String getUrl() {    return url;  }  /**   * @param url the url to set   */  public voID setUrl(String url) {    this.url = url;  }}

下载助手类：Downloader.java

package com.winton.downloadmanager;import java.io.file;import java.io.IOException;import java.io.inputStream;import java.io.RandomAccessfile;import java.net.httpURLConnection;import java.net.MalformedURLException;import java.net.URL;import java.util.ArrayList;import java.util.List;import androID.content.Context;import androID.os.Handler;import androID.os.Message;import db.Dao;import entity.DownloadInfo;import entity.LoadInfo;public class Downloader {  private String url;  private String localPath;  private int threadCount;  private Handler mHanler;  private Dao dao;  private int fileSize;  private List<DownloadInfo> infos;  private final static int INIT = 1;  private final static int DOWNLOADING =2;  private final static int PAUSE =3;  private int state = INIT;  public Downloader(String address,String lPath,int thCount,Context context,Handler handler){    url =address;    localPath = lPath;    threadCount = thCount;    mHanler = handler;    dao = new Dao(context);  }  public boolean isDownloading(){    return state == DOWNLOADING;  }  public LoadInfo getDownLoadInfos(){    if(isFirstDownload(url)){      init();      int range = fileSize/threadCount;      infos = new ArrayList<DownloadInfo>();      for(int i=0;i<=threadCount-1;i++){        DownloadInfo info = new DownloadInfo(i,i*range,(i+1)*range-1,url);        infos.add(info);      }      dao.saveInfo(infos);      return new LoadInfo(fileSize,url);    }else{      infos = dao.getInfo(url);      int size = 0;      int completeSize =0;      for(DownloadInfo info:infos){        completeSize += info.getCompleteSize();        size += info.getEndPos()-info.getStartPos()+1;      }      return new LoadInfo(size,completeSize,url);    }  }  public boolean isFirstDownload(String url){    return dao.isNewTask(url);  }  public voID init(){    try {      URL mUrl = new URL(this.url);      httpURLConnection connection = (httpURLConnection)mUrl.openConnection();      connection.setConnectTimeout(5000);      connection.setRequestMethod("GET");      fileSize = connection.getContentLength();      file file = new file(localPath);      if(!file.exists()){        file.createNewfile();      }      RandomAccessfile accessfile = new RandomAccessfile(file,"rwd");      accessfile.setLength(fileSize);      accessfile.close();      connection.disconnect();    } catch (MalformedURLException e) {      // Todo auto-generated catch block      e.printstacktrace();    } catch (IOException e) {      // Todo auto-generated catch block      e.printstacktrace();    }   }  public voID download(){    if(infos != null){      if(state ==DOWNLOADING){        return;      }      state = DOWNLOADING;      for(DownloadInfo info:infos){        new DownloadThread(info.getThreadID(),info.getUrl()).start();      }    }  }  class DownloadThread extends Thread{    private int threadID;    private int startPos;    private int endPos;    private int completeSize;    private String url;    public DownloadThread(int tID,String address) {      // Todo auto-generated constructor stub      threadID=tID;      startPos=sp;      endPos = ep;      completeSize = cSize;      url = address;    }    @OverrIDe    public voID run() {      // Todo auto-generated method stub      httpURLConnection connection = null;      RandomAccessfile randomAccessfile = null;      inputStream is = null;      try {        URL mUrl = new URL(url);        connection = (httpURLConnection)mUrl.openConnection();        connection.setConnectTimeout(5000);        connection.setRequestMethod("GET");        connection.setRequestProperty("Range","bytes="+(startPos+completeSize)+"-"+endPos);        randomAccessfile = new RandomAccessfile(localPath,"rwd");        randomAccessfile.seek(startPos+completeSize);        is=connection.getinputStream();        byte[] buffer = new byte[4096];        int length =-1;        while((length=is.read(buffer)) != -1){          randomAccessfile.write(buffer,length);          completeSize +=length;          dao.updateInfo(threadID,url);          Message msg = Message.obtain();          msg.what=1;          msg.obj=url;          msg.arg1=length;          mHanler.sendMessage(msg);          if(state==PAUSE){            return;          }        }      } catch (MalformedURLException e) {        // Todo auto-generated catch block        e.printstacktrace();      } catch (IOException e) {        // Todo auto-generated catch block        e.printstacktrace();      }finally{        try {          is.close();          randomAccessfile.close();          connection.disconnect();          dao.closeDB();        } catch (IOException e) {          // Todo auto-generated catch block          e.printstacktrace();        }      }    }  }  public voID delete(String url){    dao.deleteInfo(url);  }  public voID reset(){    state=INIT;  }  public voID pause(){    state=PAUSE;  }}

VIEw呈现类：MainActivity.java

package com.winton.downloadmanager;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.vIEw.VIEw.OnClickListener;import androID.Widget.button;import androID.Widget.Progressbar;import androID.Widget.TextVIEw;import androID.Widget.Toast;import entity.LoadInfo;public class MainActivity extends Activity implements OnClickListener{  private TextVIEw name;  private Progressbar process;  private button start,stop;  private Downloader downloader;  //处理下载进度UI的  Handler handler = new Handler(){    public voID handleMessage(androID.os.Message msg) {      if(msg.what==1){        name.setText((String)msg.obj);        int lenght = msg.arg1;        process.incrementProgressBy(lenght);      }      if(msg.what==2){        int max =msg.arg1;        process.setMax(max);        Toast.makeText(getApplicationContext(),max+"",1).show();      }    };  };  @OverrIDe  protected voID onCreate(Bundle savedInstanceState) {    super.onCreate(savedInstanceState);    setContentVIEw(R.layout.activity_main);    name=(TextVIEw)findVIEwByID(R.ID.tv_name);    process=(Progressbar)findVIEwByID(R.ID.pb_download);    start = (button)findVIEwByID(R.ID.bt_start);    stop = (button)findVIEwByID(R.ID.bt_stop);    start.setonClickListener(this);    stop.setonClickListener(this);    downloader=new Downloader("http://img4.duitang.com/uploads/item/201206/11/20120611174542_5KRMj.jpeg",Environment.getExternalStorageDirectory().getPath()+"/test1.jpg",1,getApplicationContext(),handler);  }  @OverrIDe  public voID onClick(VIEw v) {    // Todo auto-generated method stub    if(v==start){      new Thread(new Runnable() {        @OverrIDe        public voID run() {          // Todo auto-generated method stub          LoadInfo loadInfo = downloader.getDownLoadInfos();          Message msg =handler.obtainMessage();          msg.what=2;          msg.arg1=loadInfo.getfileSize();          handler.sendMessage(msg);          downloader.download();        }      }).start();      return;    }    if(v==stop){      downloader.pause();      return;    }  }  }

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。

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