断点续传之下载

//主MainActivity

public class MainActivity  extends FragmentActivity {
    private static final String TAG = MainActivity.class.getSimpleName();
    private ProgressBar mProgressBar;
    private Button start;
    private Button pause;


    private TextView total;
    private int max;
    private DownloadUtil mDownloadUtil;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        total= (TextView) findViewById(R.id.textView);
        start= (Button) findViewById(R.id.start);
        pause= (Button) findViewById(delete);
        mProgressBar= (ProgressBar) findViewById(R.id.progressBar);
        String urlString = "http://g.hiphotos.baidu.com/zhidao/pic/item/1e30e924b899a901da2aece318950a7b0308f5cc.jpg";
        String localPath = Environment.getExternalStorageDirectory()
                .getAbsolutePath() + "/local";
        mDownloadUtil = new DownloadUtil(2, localPath, "abc.jpg", urlString,
                this);
        mDownloadUtil.setOnDownloadListener(new DownloadUtil.OnDownloadListener() {

            @Override
            public void downloadStart(int fileSize) {
                // TODO Auto-generated method stub
                Log.w(TAG, "fileSize::" + fileSize);
                max = fileSize;
                mProgressBar.setMax(fileSize);
            }

            @Override
            public void downloadProgress(int downloadedSize) {
                // TODO Auto-generated method stub
                Log.w(TAG, "Compelete::" + downloadedSize);
                mProgressBar.setProgress(downloadedSize);
                total.setText((int) downloadedSize * 100 / max + "%");
            }

            @Override
            public void downloadEnd() {
                // TODO Auto-generated method stub
                Log.w(TAG, "ENd");
            }
        });
        start.setOnClickListener(new View.OnClickListener() {

            @Override
            public void onClick(View arg0) {
                // TODO Auto-generated method stub
                mDownloadUtil.start();
            }
        });
        pause.setOnClickListener(new View.OnClickListener() {

            @Override
            public void onClick(View arg0) {
                // TODO Auto-generated method stub
                mDownloadUtil.pause();
            }
        });



    }
}

//数据库

public class DownLoadHelper extends SQLiteOpenHelper{
    private static final String SQL_NAME = "download.db";
    private static final int DOWNLOAD_VERSION=1;
    public DownLoadHelper(Context context) {
        super(context, SQL_NAME, null, DOWNLOAD_VERSION);
    }

    @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 sqLiteDatabase, int i, int i1) {

    }
}

//创建下载的具体信息，得到下载具体信息，更新数据库中的下载信息，下载完成后删除数据库中的数据

public class DownlaodSqlTool {

    private DownLoadHelper dbHelper;
    public DownlaodSqlTool(Context context){
        dbHelper=new DownLoadHelper(context);

    }
    /**
     * 创建下载的具体信息
     */
    public void insertInfos(List<DownloadInfo> infos) {
        SQLiteDatabase database = dbHelper.getWritableDatabase();
        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);
        }
    }
    /**
     * 得到下载具体信息
     */
    public List<DownloadInfo> getInfos(String urlstr) {
        List<DownloadInfo> list = new ArrayList<DownloadInfo>();
        SQLiteDatabase database = dbHelper.getWritableDatabase();
        String sql = "select thread_id, start_pos, end_pos,compelete_size,url from download_info where url=?";
        Cursor 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);
        }
        return list;
    }

    /**
     * 更新数据库中的下载信息
     */
    public void updataInfos(int threadId, int compeleteSize, String urlstr) {
        SQLiteDatabase database = dbHelper.getWritableDatabase();
        String sql = "update download_info set compelete_size=? where thread_id=? and url=?";
        Object[] bindArgs = { compeleteSize, threadId, urlstr };
        database.execSQL(sql, bindArgs);
    }
    /**
     * 关闭数据库
     */
    public void closeDb() {
        dbHelper.close();
    }

    /**
     * 下载完成后删除数据库中的数据
     */
    public void delete(String url) {
        SQLiteDatabase database = dbHelper.getWritableDatabase();
        database.delete("download_info", "url=?", new String[] { url });
    }
}

//利用Http协议进行多线程下载具体实践类

public class DownloadHttpTool {
    /**
     *
     * 利用Http协议进行多线程下载具体实践类
     */

    private static final String TAG = DownloadHttpTool.class.getSimpleName();
    private int threadCount;//线程数量
    private String urlstr;//URL地址
    private Context mContext;
    private Handler mHandler;
    private List<DownloadInfo> downloadInfos;//保存下载信息的类

    private String localPath;//目录
    private String fileName;//文件名
    private int fileSize;
    private DownlaodSqlTool sqlTool;//文件信息保存的数据库操作类
    private enum Download_State {
        Downloading, Pause, Ready;//利用枚举表示下载的三种状态
    }
    private Download_State state = Download_State.Ready;//当前下载状态

    private int globalCompelete = 0;//所有线程下载的总数

    public DownloadHttpTool(int threadCount, String urlString,
                            String localPath, String fileName, Context context, Handler handler) {
        super();
        this.threadCount = threadCount;
        this.urlstr = urlString;
        this.localPath = localPath;
        this.mContext = context;
        this.mHandler = handler;
        this.fileName = fileName;
        sqlTool = new DownlaodSqlTool(mContext);
    }

    //在开始下载之前需要调用ready方法进行配置
    public void ready() {
        Log.w(TAG, "ready");
        globalCompelete = 0;
        downloadInfos = sqlTool.getInfos(urlstr);
        if (downloadInfos.size() == 0) {
            initFirst();
        } else {
            File file = new File(localPath + "/" + fileName);
            if (!file.exists()) {
                sqlTool.delete(urlstr);
                initFirst();
            } else {
                fileSize = downloadInfos.get(downloadInfos.size() - 1)
                        .getEndPos();
                for (DownloadInfo info : downloadInfos) {
                    globalCompelete += info.getCompeleteSize();
                }
                Log.w(TAG, "globalCompelete:::" + globalCompelete);
            }
        }
    }

    public void start() {
        Log.w(TAG, "start");
        if (downloadInfos != null) {
            if (state == Download_State.Downloading) {
                return;
            }
            state = Download_State.Downloading;
            for (DownloadInfo info : downloadInfos) {
                Log.v(TAG, "startThread");
                new DownloadThread(info.getThreadId(), info.getStartPos(),
                        info.getEndPos(), info.getCompeleteSize(),
                        info.getUrl()).start();
            }
        }
    }

    public void pause() {
        state = Download_State.Pause;
        sqlTool.closeDb();
    }

    public void delete(){
        compelete();
        File file = new File(localPath + "/" + fileName);
        file.delete();
    }

    public void compelete() {
        sqlTool.delete(urlstr);
        sqlTool.closeDb();
    }

    public int getFileSize() {
        return fileSize;
    }

    public int getCompeleteSize() {
        return globalCompelete;
    }

    //第一次下载初始化
    private void initFirst() {
        Log.w(TAG, "initFirst");
        try {
            URL url = new URL(urlstr);
            HttpURLConnection connection = (HttpURLConnection) url
                    .openConnection();
            connection.setConnectTimeout(5000);
            connection.setRequestMethod("GET");
            fileSize = connection.getContentLength();
            Log.w(TAG, "fileSize::" + fileSize);
            File fileParent = new File(localPath);
            if (!fileParent.exists()) {
                fileParent.mkdir();
            }
            File file = new File(fileParent, fileName);
            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();
        }
        int range = fileSize / threadCount;
        downloadInfos = new ArrayList<DownloadInfo>();
        for (int i = 0; i < threadCount - 1; i++) {
            DownloadInfo info = new DownloadInfo(i, i * range, (i + 1) * range
                    - 1, 0, urlstr);
            downloadInfos.add(info);
        }
        DownloadInfo info = new DownloadInfo(threadCount - 1, (threadCount - 1)
                * range, fileSize - 1, 0, urlstr);
        downloadInfos.add(info);
        sqlTool.insertInfos(downloadInfos);
    }
    //自定义下载线程
    private class DownloadThread extends Thread {

        private int threadId;
        private int startPos;
        private int endPos;
        private int compeleteSize;
        private String urlstr;
        private int totalThreadSize;

        public DownloadThread(int threadId, int startPos, int endPos,
                              int compeleteSize, String urlstr) {
            this.threadId = threadId;
            this.startPos = startPos;
            this.endPos = endPos;
            totalThreadSize = endPos - startPos + 1;
            this.urlstr = urlstr;
            this.compeleteSize = compeleteSize;
        }

        @Override
        public void run() {
            HttpURLConnection connection = null;
            RandomAccessFile randomAccessFile = null;
            InputStream is = null;
            try {
                randomAccessFile = new RandomAccessFile(localPath + "/"
                        + fileName, "rwd");
                randomAccessFile.seek(startPos + compeleteSize);
                URL url = new URL(urlstr);
                connection = (HttpURLConnection) url.openConnection();
                connection.setConnectTimeout(5000);
                connection.setRequestMethod("GET");
                connection.setRequestProperty("Range", "bytes="
                        + (startPos + compeleteSize) + "-" + endPos);
                is = connection.getInputStream();
                byte[] buffer = new byte[1024];
                int length = -1;
                while ((length = is.read(buffer)) != -1) {
                    randomAccessFile.write(buffer, 0, length);
                    compeleteSize += length;
                    Message message = Message.obtain();
                    message.what = threadId;
                    message.obj = urlstr;
                    message.arg1 = length;
                    mHandler.sendMessage(message);
                    sqlTool.updataInfos(threadId, compeleteSize, urlstr);
                    Log.w(TAG, "Threadid::" + threadId + "    compelete::"
                            + compeleteSize + "    total::" + totalThreadSize);
                    if (compeleteSize >= totalThreadSize) {
                        break;
                    }
                    if (state != Download_State.Downloading) {
                        break;
                    }
                }

            } catch (Exception e) {
                e.printStackTrace();
            } finally {
                try {
                    if (is != null) {
                        is.close();
                    }
                    randomAccessFile.close();
                    connection.disconnect();
                } catch (Exception e) {
                    e.printStackTrace();
                }
            }
        }
    }
}

//保存每个下载线程下载信息类

public class DownloadInfo {
    /**
     * 保存每个下载线程下载信息类
     * 
     */
    
    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;// 下载文件的URL地址
    
    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
                + "]";
    }
}

//将下载方法封装在此类， 提供下载，暂停，删除，以及重置的方法、

public class DownloadUtil {
 
    private DownloadHttpTool mDownloadHttpTool;
    private OnDownloadListener onDownloadListener;
 
    private int fileSize;
    private int downloadedSize = 0;
 
    @SuppressLint("HandlerLeak")
    private Handler mHandler = new Handler() {
 
        @Override
        public void handleMessage(Message msg) {
            // TODO Auto-generated method stub
            super.handleMessage(msg);
            int length = msg.arg1;
            synchronized (this) {//加锁保证已下载的正确性
                downloadedSize += length;
            }
            if (onDownloadListener != null) {
                onDownloadListener.downloadProgress(downloadedSize);
            }
            if (downloadedSize >= fileSize) {
                mDownloadHttpTool.compelete();
                if (onDownloadListener != null) {
                    onDownloadListener.downloadEnd();
                }
            }
        }
 
    };
 
    public DownloadUtil(int threadCount, String filePath, String filename,
            String urlString, Context context) {
 
        mDownloadHttpTool = new DownloadHttpTool(threadCount, urlString,
                filePath, filename, context, mHandler);
    }
 
    //下载之前首先异步线程调用ready方法获得文件大小信息，之后调用开始方法
    public void start() {
        new AsyncTask<Void,Void,Void>() {
 
            @Override
            protected Void doInBackground(Void... arg0) {
                // TODO Auto-generated method stub
                mDownloadHttpTool.ready();
                return null;
            }
 
            @Override
            protected void onPostExecute(Void result) {
                // TODO Auto-generated method stub
                super.onPostExecute(result);
                fileSize = mDownloadHttpTool.getFileSize();
                downloadedSize = mDownloadHttpTool.getCompeleteSize();
                Log.w("Tag", "downloadedSize::" + downloadedSize);
                if (onDownloadListener != null) {
                    onDownloadListener.downloadStart(fileSize);
                }
                mDownloadHttpTool.start();
            }
        }.execute();
    }
 
    public void pause() {
        mDownloadHttpTool.pause();
    }
     
    public void delete(){
        mDownloadHttpTool.delete();
    }
 
    public void reset(){
        mDownloadHttpTool.delete();
        start();
    }
     
    public void setOnDownloadListener(OnDownloadListener onDownloadListener) {
        this.onDownloadListener = onDownloadListener;
    }
 
    //下载回调接口
    public interface OnDownloadListener {
        public void downloadStart(int fileSize);
 
        public void downloadProgress(int downloadedSize);//记录当前所有线程下总和
 
        public void downloadEnd();
    }
}

//所需添加的权限

  <uses-sdk
        android:minSdkVersion="8"
        android:targetSdkVersion="18" />

    <uses-permission android:name="android.permission.MOUNT_UNMOUNT_FILESYSTEMS" />
    <uses-permission android:name="android.permission.READ_EXTERNAL_STORAGE"/>
    <uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE"/>
    <uses-permission android:name="android.permission.INTERNET"/>