Android-断点续传

断点续传原理

在本地下载过程中要使用数据库实时存储到底存储到文件的哪个位置了，这样点击开始继续传递时，才能通过HTTP的GET请求中的setRequestProperty()方法可以告诉服务器，数据从哪里开始，到哪里结束。
同时在本地的文件写入时，RandomAccessFile的seek()方法也支持在文件中的任意位置进行写入操作。
同时通过广播将子线程的进度告诉Activity的ProcessBar。

通过设置网络请求参数，请求服务器从指定的位置开始读取数据。
而要实现这两个功能只需要使用到httpURLconnection里面的setRequestProperty方法便可以实现.

public void setRequestProperty(String field, String newValue)

如下所示，便是向服务器请求500-1000之间的500个byte：

conn.setRequestProperty("Range", "bytes=" + 500 + "-" + 1000);

以上只是续传的一部分需求，当我们获取到下载数据时，还需要将数据写入文件，而普通发File对象并不提供从指定位置写入数据的功能，这个时候，就需要使用到RandomAccessFile来实现从指定位置给文件写入数据的功能。

public void seek(long offset)

如下所示，便是从文件的的第100个byte后开始写入数据。

raFile.seek(100);

而开始写入数据时还需要用到RandomAccessFile里面的另外一个方法

public void write(byte[] buffer, int byteOffset, int byteCount)

该方法的使用和OutputStream的write的使用一模一样.

设计思路：

1.多线程下载：

首先通过下载总线程数来划分文件的下载区域：利用int range = fileSize / threadCount；得到每一段下载量；每一段的位置是i * range到(i + 1) * rang - 1，注意最后一段的位置是到filesize - 1；
通过Http协议的Range字段实现下载文件的分段；
通过Java类RandomAccessFile可以实现文件的随机访问，利用seek方法定位的文件的指定位置；
由HttpUrlConnection获取流来进行流的读写，实现文件的存储；
在下载过程中利用Handler来向外传递下载的信息。

2.断点续传：

对于每一个线程利用一个DownloadInfo类来保存下载的信息，每次在下载过程中向数据库更新信息（我也有想过只在下载暂停时进行更新，但那样的话我们的进程被杀掉时信息就无法保存下来）。在进行下载之前去访问数据库是否有记录存在，如果没有执行第一次下载的初始化，如果存在记录但下载文件不存在时，删掉数据库中的记录之后进行第一次下载的初始化，如果有记录且文件存在，则从数据库中取出信息。

demo下载地址：断点续传

示例：

主要类的结构有：
1）DownloadHttpTool：利用Http协议进行网络下载类
2）DownlaodSqlTool， DownLoadHelper：数据库相关操作类
3）DownloadInfo：下载信息保存类
4）DownloadUtil：封装下载方法并提供对外接口的类

DownLoadHelper 类：

package com.example.test;import android.content.Context;import android.database.sqlite.SQLiteDatabase;import android.database.sqlite.SQLiteOpenHelper;/** * 利用数据库来记录下载信息 * * @author acer */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);    }    /**     * 在download.db数据库下创建一个download_info表存储下载信息     */    @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 db, int oldVersion, int newVersion) {    }}

DownlaodSqlTool 类：

package com.example.test;import java.util.ArrayList;import java.util.List;import android.content.Context;import android.database.Cursor;import android.database.sqlite.SQLiteDatabase;/** *  * 数据库操作工具类 */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 });    }}

DownloadInfo ：

package com.example.test;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                + "]";    }}

DownloadHttpTool 类：

package com.example.test;import java.io.File;import java.io.InputStream;import java.io.RandomAccessFile;import java.net.HttpURLConnection;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 android.util.Log;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();                }            }        }    }}

DownloadUtil

package com.example.test;import android.annotation.SuppressLint;import android.content.Context;import android.os.AsyncTask;import android.os.Handler;import android.os.Message;import android.util.Log;/** * 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) {            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);        public void downloadEnd();    }}

MainActivity ：

package com.example.test;import android.os.Bundle;import android.os.Environment;import android.support.v4.app.FragmentActivity;import android.util.Log;import android.view.View;import android.view.View.OnClickListener;import android.widget.Button;import android.widget.ProgressBar;import android.widget.TextView;import com.example.test.DownloadUtil.OnDownloadListener;public class MainActivity extends FragmentActivity {    private static final String TAG = MainActivity.class.getSimpleName();    private ProgressBar mProgressBar;    private Button start;    private Button pause;    private Button delete;    private Button reset;    private TextView total;    private int max;    private DownloadUtil mDownloadUtil;    String urlString = "http://bbra.cn/Uploadfiles/imgs/20110303/fengjin/013.jpg";    String localPath = Environment.getExternalStorageDirectory()            .getAbsolutePath() + "/local";    @Override    protected void onCreate(Bundle savedInstanceState) {        super.onCreate(savedInstanceState);        setContentView(R.layout.activity_main);        mProgressBar = (ProgressBar) findViewById(R.id.progressBar1);        start = (Button) findViewById(R.id.button_start);        pause = (Button) findViewById(R.id.button_pause);        delete = (Button) findViewById(R.id.button_delete);        reset = (Button) findViewById(R.id.button_reset);        total = (TextView) findViewById(R.id.textView_total);        mDownloadUtil = new DownloadUtil(2, localPath, "abc.jpg", urlString,                this);        mDownloadUtil.setOnDownloadListener(new OnDownloadListener() {            @Override            public void downloadStart(int fileSize) {                Log.w(TAG, "fileSize::" + fileSize);                max = fileSize;                mProgressBar.setMax(fileSize);            }            @Override            public void downloadProgress(int downloadedSize) {                Log.w(TAG, "Compelete::" + downloadedSize);                mProgressBar.setProgress(downloadedSize);                total.setText((int) downloadedSize * 100 / max + "%");            }            @Override            public void downloadEnd() {                Log.w(TAG, "ENd");            }        });        start.setOnClickListener(new OnClickListener() {            @Override            public void onClick(View arg0) {                mDownloadUtil.start();            }        });        pause.setOnClickListener(new OnClickListener() {            @Override            public void onClick(View arg0) {                mDownloadUtil.pause();            }        });        delete.setOnClickListener(new OnClickListener() {            @Override            public void onClick(View arg0) {                mDownloadUtil.delete();            }        });        reset.setOnClickListener(new OnClickListener() {            @Override            public void onClick(View arg0) {                mDownloadUtil.reset();            }        });    }}

布局：

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"    xmlns:tools="http://schemas.android.com/tools"    android:layout_width="fill_parent"    android:layout_height="fill_parent"    android:padding="30dp">    <ProgressBar        android:id="@+id/progressBar1"        style="?android:attr/progressBarStyleHorizontal"        android:layout_width="match_parent"        android:layout_height="wrap_content" />    <Button        android:id="@+id/button_start"        android:layout_width="wrap_content"        android:layout_height="wrap_content"        android:layout_alignRight="@+id/progressBar1"        android:layout_below="@+id/progressBar1"        android:layout_marginTop="32dp"        android:text="开始" />    <Button        android:id="@+id/button_pause"        android:layout_width="wrap_content"        android:layout_height="wrap_content"        android:layout_alignBaseline="@+id/button_start"        android:layout_alignBottom="@+id/button_start"        android:layout_toLeftOf="@+id/button_start"        android:text="暂停" />    <TextView        android:id="@+id/textView_total"        android:layout_width="wrap_content"        android:layout_height="wrap_content"        android:layout_above="@+id/button_pause"        android:layout_alignLeft="@+id/progressBar1"        android:text="0%" />    <Button        android:id="@+id/button_delete"        android:layout_width="wrap_content"        android:layout_height="wrap_content"        android:layout_alignBaseline="@+id/button_pause"        android:layout_alignBottom="@+id/button_pause"        android:layout_toLeftOf="@+id/button_pause"        android:text="删除" />    <Button        android:id="@+id/button_reset"        android:layout_width="wrap_content"        android:layout_height="wrap_content"        android:layout_alignRight="@+id/button_start"        android:layout_below="@+id/button_start"        android:layout_marginTop="18dp"        android:text="重新下载" /></RelativeLayout>

参考：

Android开发——断点续传原理以及实现

Android开发–多线程下载加断点续传