Android实现断点下载的方法

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;  }}

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  }}

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,start_pos,end_pos,complete_size,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();  }}

package entity;public class LoadInfo {  private int fileSize;  private int completeSize;    private String url;  public LoadInfo(int fs,int cSize,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;  }}

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, 0, url);        infos.add(info);      }      dao.saveInfo(infos);      return new LoadInfo(fileSize, 0, 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.getStartPos(), info.getEndPos(), info.getCompleteSize(), 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,int sp,int ep,int cSize,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, 0, length);          completeSize +=length;          dao.updateInfo(threadId, completeSize, 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;  }}

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;    }  }  }