Android断点下载实现

引言

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,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();    }}

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,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;    }}

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, 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;    }}

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。

总结

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。