Android 文件下载（断点、多任务并行下载）

以下代码是基于百度云网盘：http://pan.baidu.com/s/1dD1Xo8T 中的demo进行优化及功能添加。
以下代码实现功能有：多线程下载、多任务并行下载以及下载进度和下载速度的显示等功能。
实现思路：根据线程数分割待下载文件；利用HttpURLConnection实现各部分文件的下载；利用RandomAccessFile实现下载内容的保存；各线程下载任务信息保存在数据库，以便暂停和恢复下载。
demo已上传到github：https://github.com/shichaohui/FileDownloadDemo.git 欢迎下载。
效果图：

主要代码

DownLoadHelper.java:

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 [e-mail] */public class DownLoadHelper extends SQLiteOpenHelper {    private static final String DB_NAME = "download.db";    private static final String TB_NAME = "download_info";    private static final int DOWNLOAD_VERSION = 1;    public DownLoadHelper(Context context) {        super(context, DB_NAME, null, DOWNLOAD_VERSION);    }    @Override    public void onCreate(SQLiteDatabase db) {        db.execSQL("create table "                + TB_NAME                + "(_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) {    }}

这个类没什么好说的，就是创建数据库和数据表。

DownlaodSqlTool.java

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 *  * @author [e-mail] */public class DownlaodSqlTool {    private static DownlaodSqlTool instance = null;    private DownLoadHelper dbHelper = null;    private DownlaodSqlTool(Context context) {        dbHelper = new DownLoadHelper(context);    }    private static synchronized void syncInit(Context context) {        if (instance == null) {            instance = new DownlaodSqlTool(context);        }    }    public static DownlaodSqlTool getInstance(Context context) {        if (instance == null) {            syncInit(context);        }        return instance;    }    /** 将下载的进度等信息保存到数据库 */    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);        }    }    /** 获取下载的进度等信息 */    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);        }        cursor.close();        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();    }    /** 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 });    }}

单例模式的数据库操作类，主要实现数据的增删改查等操作。

DownloadInfo.java

package com.example.test;/** * 保存每个下载线程下载信息类 *  * @author [e-mail] */public class DownloadInfo {    private int threadId; // 下载线程的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    /**     *      * @param threadId     *            下载线程的id     * @param startPos     *            开始点     * @param endPos     *            结束点     * @param compeleteSize     *            // 已下载的大小     * @param url     *            下载地址     */    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() {    }    /** 获取下载地址 */    public String getUrl() {        return url;    }    public void setUrl(String url) {        this.url = url;    }    /** 获取下载线程的Id */    public int getThreadId() {        return threadId;    }    public void setThreadId(int threadId) {        this.threadId = threadId;    }    /** 获取下载的开始位置 */    public int getStartPos() {        return startPos;    }    public void setStartPos(int startPos) {        this.startPos = startPos;    }    /** 获取下载的结束位置 */    public int getEndPos() {        return endPos;    }    public void setEndPos(int endPos) {        this.endPos = endPos;    }    /** 获取已下载的大小 */    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                + "]";    }}

下载实体类，针对于单个下载线程，保存下载线程对应的文件相关信息，比如当前下载线程负责下载的部分是从文件的哪个点开始的（startPos）、哪个点结束的（endPos）以及当前已经下载了多少（compeleteSize）等信息。

DownloadingInfo.java

package com.example.test;/** * 某一任务正在下载时的信息 *  * @author [e-mail] *  */public class DownloadingInfo {    private String kbps = "0"; // 每秒下载速度    private int secondSize = 0; // 一秒钟累计下载量    private int fileSize = 0; // 文件大小    public String getKbps() {        return kbps;    }    public void setKbps(String kbps) {        this.kbps = kbps;    }    public int getSecondSize() {        return secondSize;    }    public void setSecondSize(int secondSize) {        this.secondSize = secondSize;    }    public int getFileSize() {        return fileSize;    }    public void setFileSize(int fileSize) {        this.fileSize = fileSize;    }    @Override    public String toString() {        return "DownloadingInfo [kbps=" + kbps + ", secondSize=" + secondSize                + ", fileSize=" + fileSize + "]";    }}

这也是一个下载相关的实体类，针对于一个下载任务（包括多个下载线程）。保存下载任务的下载进度、速度等用于客户端显示的数据。

DownloadHttpTool.java

package com.example.test;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.AsyncTask;import android.os.Environment;import android.os.Handler;import android.os.Message;/** * 利用Http协议进行多线程下载具体实现类 *  * @author [e-mail] */public class DownloadHttpTool {    private final int THREAD_COUNT = 2; // 线程数量    private String urlstr = ""; // URL地址    private Context mContext = null;    private List<DownloadInfo> downloadInfos = null; // 保存下载信息的类    /** 下载文件保存路径 */    public static String filePath = ""; // 目录    private String fileName = ""; // 文件名    private String fileNameTmp = ""; // 临时文件名    /** 临时文件名后缀 */    public static final String FILE_TMP_SUFFIX = ".tmp";    private int fileSize = 0; // 文件大小    private DownlaodSqlTool sqlTool = null; // 文件信息保存的数据库操作类    private DownloadComplated downloadComplated = null;    private int totalCompelete = 0;// 所有线程已下载的总数    private List<DownloadThread> threads = null; // 下载线程    private Handler handler = null;    // 利用枚举表示下载的几种状态    private enum Download_State {        Downloading, Pause, Ready, Compeleted, Exception;    }    private Download_State state = Download_State.Ready; // 当前下载状态    /**     * @param context     *            上下文对象     * @param downloadComplated     */    public DownloadHttpTool(Context context, Handler handler,            DownloadComplated downloadComplated) {        super();        this.mContext = context;        this.handler = handler;        this.downloadComplated = downloadComplated;        sqlTool = DownlaodSqlTool.getInstance(mContext);        if ("".equals(filePath)) {            // TODO 根据有无sdcard设置路径            filePath = Environment.getExternalStorageDirectory()                    .getAbsolutePath() + "/meiriq-download";        }        threads = new ArrayList<DownloadThread>();    }    /**     * 开始下载     *      * @param url     *            下载地址     */    public void start(String urlstr) {        this.urlstr = urlstr;        String[] ss = urlstr.split("/");        fileName = ss[ss.length - 1];        fileNameTmp = fileName + FILE_TMP_SUFFIX;        new AsyncTask<Void, Void, Void>() {            @Override            protected Void doInBackground(Void... arg0) {                // 下载之前首先异步线程调用ready方法做下载的准备工作                ready();                Message msg = new Message();                msg.what = 1;                msg.arg1 = fileSize;                msg.obj = DownloadHttpTool.this.urlstr;                handler.sendMessage(msg);                return null;            }            @Override            protected void onPostExecute(Void result) {                super.onPostExecute(result);                // 开始下载                startDownload();            }        }.execute();    }    /** 在开始下载之前需要调用ready方法进行配置 */    private void ready() {        if (new File(filePath + "/" + fileName).exists()) {            downloadComplated.onComplated(urlstr);            return;        }        totalCompelete = 0;        downloadInfos = sqlTool.getInfos(urlstr);        if (downloadInfos.size() == 0) { // 数据库中没有相关信息            initFirst();        } else {            File file = new File(filePath + "/" + fileNameTmp);            if (!file.exists()) {                sqlTool.delete(urlstr);                initFirst();            } else {                fileSize = downloadInfos.get(downloadInfos.size() - 1)                        .getEndPos();                for (DownloadInfo info : downloadInfos) {                    totalCompelete += info.getCompeleteSize();                }            }        }    }    /** 开始下载 */    private void startDownload() {        if (downloadInfos != null) {            if (state == Download_State.Downloading) {                return;            }            state = Download_State.Downloading;            for (DownloadInfo info : downloadInfos) { // 开启线程下载                DownloadThread thread = new DownloadThread(info.getThreadId(),                        info.getStartPos(), info.getEndPos(),                        info.getCompeleteSize(), info.getUrl());                thread.start();                threads.add(thread);            }        }    }    /** 暂停当前下载任务 */    public void pause() {        state = Download_State.Pause;    }    /** 删除当前下载任务 */    public void delete() {        compeleted();        File file = new File(filePath + "/" + fileNameTmp);        file.delete();    }    /** 完成下载 */    private void compeleted() {        state = Download_State.Compeleted;        sqlTool.delete(urlstr);        downloadComplated.onComplated(urlstr);    }    /** 获取目标文件大小 */    public int getFileSize() {        return fileSize;    }    /** 获取当前下载的大小 */    public int getTotalCompeleteSize() {        return totalCompelete;    }    /** 第一次下载时进行的初始化 */    private void initFirst() {        URL url = null;        RandomAccessFile accessFile = null;        HttpURLConnection connection = null;        try {            url = new URL(urlstr);            connection = (HttpURLConnection) url.openConnection();            connection.setConnectTimeout(5000);            connection.setRequestMethod("GET");            fileSize = connection.getContentLength();            if (fileSize < 0) {                return;            }            File fileParent = new File(filePath);            if (!fileParent.exists()) {                fileParent.mkdir();            }            File file = new File(fileParent, fileNameTmp);            if (!file.exists()) {                file.createNewFile();            }            // 随机访问文件            accessFile = new RandomAccessFile(file, "rwd");            accessFile.setLength(fileSize);        } catch (MalformedURLException e) {            e.printStackTrace();        } catch (IOException e) {            e.printStackTrace();        } finally {            if (accessFile != null) {                try {                    accessFile.close();                } catch (IOException e) {                    e.printStackTrace();                }            }            if (connection != null) {                connection.disconnect();            }        }        // 计算每个线程需要下载的大小        int range = fileSize / THREAD_COUNT;        // 保存每个线程的下载信息        downloadInfos = new ArrayList<DownloadInfo>();        for (int i = 0; i < THREAD_COUNT - 1; i++) {            DownloadInfo info = new DownloadInfo(i, i * range, (i + 1) * range                    - 1, 0, urlstr);            downloadInfos.add(info);        }        // 最后一个线程和前面的处理有点不一样        DownloadInfo info = new DownloadInfo(THREAD_COUNT - 1,                (THREAD_COUNT - 1) * range, fileSize - 1, 0, urlstr);        downloadInfos.add(info);        // 插入到数据库        sqlTool.insertInfos(downloadInfos);    }    interface DownloadComplated {        /**         * 下载完成回调         *          * @param urlString         */        void onComplated(String urlString);    }    /** 自定义下载线程 */    private class DownloadThread extends Thread {        private int threadId = 0; // 线程Id        private int startPos = 0; // 在文件中的开始的位置        private int endPos = 0; // 在文件中的结束的位置        private int compeleteSize = 0; // 已完成下载的大小        private String urlstr = ""; // 下载地址        /**         *          * @param threadId         *            线程Id         * @param startPos         *            在文件中的开始的位置         * @param endPos         *            在文件中的结束的位置         * @param compeleteSize         *            已完成下载的大小         * @param urlstr         *            下载地址         */        public DownloadThread(int threadId, int startPos, int endPos,                int compeleteSize, String urlstr) {            this.threadId = threadId;            this.startPos = startPos;            this.endPos = endPos;            this.urlstr = urlstr;            this.compeleteSize = compeleteSize;        }        @Override        public void run() {            HttpURLConnection connection = null;            RandomAccessFile randomAccessFile = null;            InputStream is = null;            try {                randomAccessFile = new RandomAccessFile(filePath + "/"                        + fileNameTmp, "rwd");                randomAccessFile.seek(startPos + compeleteSize);                URL url = new URL(urlstr);                connection = (HttpURLConnection) url.openConnection();                connection.setConnectTimeout(5000);                connection.setRequestMethod("GET");                // 设置请求的数据的范围                connection.setRequestProperty("Range", "bytes="                        + (startPos + compeleteSize) + "-" + endPos);                is = connection.getInputStream();                byte[] buffer = new byte[6 * 1024]; // 6K的缓存                int length = -1;                while ((length = is.read(buffer)) != -1) {                    randomAccessFile.write(buffer, 0, length); // 写缓存数据到文件                    compeleteSize += length;                    synchronized (this) { // 加锁保证已下载的正确性                        totalCompelete += length;                        Message msg = new Message();                        msg.what = 0;                        msg.arg1 = length;                        msg.arg2 = totalCompelete;                        msg.obj = urlstr;                        handler.sendMessage(msg);                    }                    // 非正在下载状态时跳出循环                    if (state != Download_State.Downloading) {                        break;                    }                }            } catch (Exception e) {                e.printStackTrace();                System.out.println("异常退出____" + urlstr);                state = Download_State.Exception;            } finally {                // 不管发生了什么事，都要保存下载信息到数据库                sqlTool.updataInfos(threadId, compeleteSize, urlstr);                if (threads.size() == 1) { // 当前线程是此url对应下载任务唯一一个正在执行的线程                    try {                        if (is != null) {                            is.close();                        }                        if (randomAccessFile != null) {                            randomAccessFile.close();                        }                        if (connection != null) {                            connection.disconnect();                        }                    } catch (Exception e) {                        e.printStackTrace();                    }                    if (state == Download_State.Downloading) { // 此时此线程的下载任务正常完成（没有被人为或异常中断）                        File file = new File(filePath + "/" + fileNameTmp);                        file.renameTo(new File(filePath + "/" + fileName));                    }                    if (state != Download_State.Pause) {                        compeleted();                    }                }                threads.remove(this);            }        }    }}

一个DownloadHttpTool的实例表示一个下载任务，一个下载任务中可以有多个下载线程，可以通过修改常量THREAD_COUNT的方式修改一个下载任务的下载线程数。文件的保存路径是在sdcard中的meiriq-download文件夹，也可以修改到其他路径。
此类中在下载开始的时候首先会执行ready()方法获取文件相关的信息，之后执行startDownload()开启下载线程执行下载。
下载时使用HttpURLConnection类的setRequestProperty方法指定请求头字段实现文件的随机下载（下载从某一个点开始到某一个点结束之际的内容），使用RandomAccessFile实现文件的随机访问（可以从某一个点开始写入数据）。
为了保证下载速度，写入数据库的操作并不是每次写入文件之后都执行，而是在下载出现异常或者暂停等操作之后才写入数据库。所有下载任务全部结束后执行关闭数据流等操作。

DownloadUtil.java

package com.example.test;import java.io.File;import java.util.ArrayList;import java.util.HashMap;import java.util.List;import java.util.Map;import java.util.Map.Entry;import android.content.Context;import android.os.Handler;import android.os.Message;import com.example.test.DownloadHttpTool.DownloadComplated;/** * 将下载方法封装在此类 提供开始、暂停、删除以及重置的方法。<br> * 通过修改常量{@link DownloadUtil#MAX_COUNT}可改变最大并行下载任务量 *  * @author [e-mail] */public class DownloadUtil {    private static DownloadUtil instance = null;    private Context context = null;    private List<String> downloadList = null;    private Map<String, DownloadHttpTool> downloadMap = null;    private int currentUrlIndex = -1;    private final int MAX_COUNT = 2; // 最大并行下载量    private int currentCount = 0; // 当前并行下载量    private final String FLAG_FREE = "free"; // 标记downloadMap中空闲的DownloadHttpTool实例    private OnDownloadListener onDownloadListener = null;    private Handler mHandler = new Handler() {        @Override        public void handleMessage(Message msg) {            super.handleMessage(msg);            String url = msg.obj.toString();            if (msg.what == 0) {                if (onDownloadListener != null) {                    onDownloadListener                            .downloadProgress(url, msg.arg2, msg.arg1);                }            } else if (msg.what == 1) {                if (onDownloadListener != null) {                    onDownloadListener.downloadStart(url, msg.arg1);                }            } else if (msg.what == 2) {                onDownloadListener.downloadEnd(url);            }        }    };    private DownloadUtil(Context context) {        this.context = context;        downloadList = new ArrayList<String>();        downloadMap = new HashMap<String, DownloadHttpTool>();    }    private static synchronized void syncInit(Context context) {        if (instance == null) {            instance = new DownloadUtil(context);        }    }    public static DownloadUtil getInstance(Context context) {        if (instance == null) {            syncInit(context);        }        return instance;    }    /**     * 下载之前的准备工作，并自动开始下载     *      * @param context     */    public void prepare(String urlString) {        downloadList.add(urlString);        if (currentCount < MAX_COUNT) {            start();        } else {            System.out.println("等待下载____" + urlString);        }    }    /**     * 开始下载     */    private synchronized void start() {        if (++currentUrlIndex >= downloadList.size()) {            currentUrlIndex--;            return;        }        currentCount++;        String urlString = downloadList.get(currentUrlIndex);        System.out.println("开始下载____" + urlString);        DownloadHttpTool downloadHttpTool = null;        if (downloadMap.size() < MAX_COUNT) { // 保证downloadMap.size() <= 2            downloadHttpTool = new DownloadHttpTool(context, mHandler,                    downloadComplated);            if (downloadMap.containsKey(urlString)) {                downloadMap.remove(urlString);            }            downloadMap.put(urlString, downloadHttpTool);        } else {            downloadHttpTool = downloadMap.get(FLAG_FREE);            downloadMap.remove(FLAG_FREE);            downloadMap.put(urlString, downloadHttpTool);        }        downloadHttpTool.start(urlString);    }    /** 暂停当前下载任务 */    public void pause(String urlString) {        paused(urlString, new Paused() {            @Override            public void onPaused(DownloadHttpTool downloadHttpTool) {                downloadHttpTool.pause();            }        });    }    /** 暂停所有的下载任务 */    public void pauseAll() {        // 如果需要边遍历集合边删除数据，需要从后向前遍历，否则会出异常（Caused by:        // java.util.ConcurrentModificationException）        String[] keys = new String[downloadMap.size()];        downloadMap.keySet().toArray(keys);        for (int i = keys.length - 1; i >= 0; i--) {            pause(keys[i]);        }        instance = null;    }    /**     * 恢复当前下载任务     *      * @param urlString     *            要恢复下载的文件的地址     */    public void resume(String urlString) {        prepare(urlString);    }    /** 恢复所有的下载任务 */    public void resumeAll() {        for (Entry<String, DownloadHttpTool> entity : downloadMap.entrySet()) {            prepare(entity.getKey());        }    }    /** 删除当前下载任务 */    public void delete(String urlString) {        boolean bool = paused(urlString, new Paused() {            @Override            public void onPaused(DownloadHttpTool downloadHttpTool) {                downloadHttpTool.pause();                downloadHttpTool.delete();            }        });        if (!bool) { // 下载任务不存在，直接删除临时文件            File file = new File(DownloadHttpTool.filePath + "/"                    + urlString.split("/")[urlString.split("/").length - 1]                    + DownloadHttpTool.FILE_TMP_SUFFIX);            System.out.println(file.delete());        }    }    interface Paused {        void onPaused(DownloadHttpTool downloadHttpTool);    }    /**     * 暂停     *      * @param urlString     * @param paused     * @return 下载任务是否存在的标识     */    private boolean paused(String urlString, Paused paused) {        if (downloadMap.containsKey(urlString)) {            currentCount--;            DownloadHttpTool downloadHttpTool = downloadMap.get(urlString);            paused.onPaused(downloadHttpTool);            if (!downloadMap.containsKey(FLAG_FREE)) { // 保证key == FLAG_FREE的数量                                                        // = 1                downloadMap.put(FLAG_FREE, downloadHttpTool);            }            downloadMap.remove(urlString);            start();            return true;        }        return false;    }    DownloadComplated downloadComplated = new DownloadComplated() {        @Override        public void onComplated(String urlString) {            System.out.println("下载完成____" + urlString);            Message msg = new Message();            msg.what = 2;            msg.obj = urlString;            mHandler.sendMessage(msg);            pause(urlString);            // 满足此条件说明全部下载结束            if (downloadMap.size() == 1 && downloadMap.containsKey(FLAG_FREE)) {                System.out.println("全部下载结束");            }        }    };    /** 设置下载监听 */    public void setOnDownloadListener(OnDownloadListener onDownloadListener) {        this.onDownloadListener = onDownloadListener;    }    /** 下载回调接口 */    public interface OnDownloadListener {        /**         * 下载开始回调接口         *          * @param url         * @param fileSize         *            目标文件大小         */        public void downloadStart(String url, int fileSize);        /**         * 下载进度回调接口         *          * @param         * @param downloadedSize         *            已下载大小         * @param lenth         *            本次下载大小         */        public void downloadProgress(String url, int downloadedSize, int length);        /**         * 下载完成回调         *          * @param url         */        public void downloadEnd(String url);    }}

一个单例的类封了”开始“、”暂停“、”继续“、”删除“等下载任务相关操作方法，管理所有下载任务；利用Handler实现下载进度等信息的更新；常量FLAG_FREE标识空闲下载任务；可通过修改常量MAX_COUNT的值的方式修改最大并行下载任务数。
该类管理下载任务的方式：获取该类实例后调用prepare(String urlString)方法添加下载任务，如果没有达到最大并行下载数，则会执行start()开始下载，否则等待其他下载任务下载完成后下载；当一个任务被暂停、删除或者下载完成后执行start()开始新的下载。集合downloadMap保存所有的下载任务，最多MAX_COUNT个。当一个下载任务完成后downloadMap中对应的下载任务变为FLAG_FREE以便后来的任务重复使用，如果FLAG_FREE的任务已存在则直接删除此任务。

MainActivity.java

package com.example.test;import java.text.DecimalFormat;import java.util.ArrayList;import java.util.HashMap;import java.util.List;import java.util.Map;import java.util.Map.Entry;import java.util.Timer;import java.util.TimerTask;import android.os.Bundle;import android.support.v4.app.FragmentActivity;import android.view.LayoutInflater;import android.view.View;import android.view.View.OnClickListener;import android.view.ViewGroup;import android.widget.BaseAdapter;import android.widget.Button;import android.widget.ListView;import android.widget.ProgressBar;import android.widget.TextView;import com.example.test.DownloadUtil.OnDownloadListener;public class MainActivity extends FragmentActivity implements OnClickListener {    private ListView listView = null;    private List<String> urls = null;    private DownloadUtil downloadUtil = null;    private final String TAG_PROGRESS = "_progress";    private final String TAG_TOTAL = "_total";    @Override    protected void onCreate(Bundle savedInstanceState) {        super.onCreate(savedInstanceState);        setContentView(R.layout.activity_main);        listView = (ListView) findViewById(R.id.listview);        urls = new ArrayList<String>();        urls.add("http://pc1.gamedog.cn/big/game/dongzuo/102631/shenmiaotw2_yxdog.apk");        urls.add("http://pc1.gamedog.cn/big/game/yizhi/67450/baoweiluobo_an_yxdog.apk");        urls.add("http://pc1.gamedog.cn/big/game/yizhi/161623/zhiwudzjs2gqb_an.apk");        listView.setAdapter(myAdapter);        downloadUtil = DownloadUtil.getInstance(this);        downloadUtil.setOnDownloadListener(new OnDownloadListener() {            String text = "已下载%sM / 共%sM \n占比%s  \n下载速度%skb/s";            DecimalFormat decimalFormat = new DecimalFormat("#.##"); // 小数格式化            Timer timer = null;            Map<String, DownloadingInfo> downloadingInfos = new HashMap<String, DownloadingInfo>();            @Override            public void downloadStart(String url, int fileSize) {                DownloadingInfo info = new DownloadingInfo();                info.setFileSize(fileSize);                downloadingInfos.put(url, info);                ((ProgressBar) listView.findViewWithTag(url + TAG_PROGRESS))                        .setMax(fileSize);            }            @Override            public synchronized void downloadProgress(String url,                    int downloadedSize, int length) {                DownloadingInfo info = downloadingInfos.get(url);                if (info != null) {                    ((ProgressBar) listView.findViewWithTag(url + TAG_PROGRESS))                            .setProgress(downloadedSize);                    ((TextView) listView.findViewWithTag(url + TAG_TOTAL)).setText(String.format(                            text,                            decimalFormat                                    .format(downloadedSize / 1024.0 / 1024.0),                            decimalFormat.format(info.getFileSize() / 1024.0 / 1024.0),                            (int) (((float) downloadedSize / (float) info                                    .getFileSize()) * 100) + "%", info                                    .getKbps()));                    info.setSecondSize(info.getSecondSize() + length);                }                if (timer == null) {                    timer = new Timer();                    timer.schedule(new TimerTask() {                        @Override                        public void run() {                            DownloadingInfo info = null;                            for (Entry<String, DownloadingInfo> entry : downloadingInfos                                    .entrySet()) {                                info = entry.getValue();                                if (info != null) {                                    info.setKbps(decimalFormat.format(info                                            .getSecondSize() / 1024.0));                                    info.setSecondSize(0);                                }                            }                        }                    }, 0, 1000);                }            }            @Override            public void downloadEnd(String url) {                DownloadingInfo info = downloadingInfos.get(url);                if (info != null) {                    ((ProgressBar) listView.findViewWithTag(url + TAG_PROGRESS))                            .setProgress(info.getFileSize());                    ((TextView) listView.findViewWithTag(url + TAG_TOTAL))                            .setText(String.format(                                    text,                                    decimalFormat.format(info.getFileSize() / 1024.0 / 1024.0),                                    decimalFormat.format(info.getFileSize() / 1024.0 / 1024.0),                                    "100%", info.getKbps()));                    downloadingInfos.remove(url);                }            }        });    }    BaseAdapter myAdapter = new BaseAdapter() {        @Override        public View getView(int position, View convertView, ViewGroup parent) {            Holder holder = null;            if (convertView == null) {                convertView = LayoutInflater.from(MainActivity.this).inflate(                        R.layout.list_item, null);                holder = new Holder();                holder.tv_url = (TextView) convertView.findViewById(R.id.url);                holder.progressBar = (ProgressBar) convertView                        .findViewById(R.id.progressBar);                holder.textView_total = (TextView) convertView                        .findViewById(R.id.textView_total);                holder.button_start = (Button) convertView                        .findViewById(R.id.button_start);                holder.button_pause = (Button) convertView                        .findViewById(R.id.button_pause);                holder.button_resume = (Button) convertView                        .findViewById(R.id.button_resume);                holder.button_delete = (Button) convertView                        .findViewById(R.id.button_delete);                convertView.setTag(holder);                setClick(holder);            } else {                holder = (Holder) convertView.getTag();            }            holder.tv_url.setText(urls.get(position));            holder.progressBar.setTag(urls.get(position) + TAG_PROGRESS);            holder.textView_total.setTag(urls.get(position) + TAG_TOTAL);            holder.button_start.setTag(urls.get(position));            holder.button_pause.setTag(urls.get(position));            holder.button_resume.setTag(urls.get(position));            holder.button_delete.setTag(urls.get(position));            return convertView;        }        private void setClick(Holder holder) {            holder.button_start.setOnClickListener(MainActivity.this);            holder.button_pause.setOnClickListener(MainActivity.this);            holder.button_resume.setOnClickListener(MainActivity.this);            holder.button_delete.setOnClickListener(MainActivity.this);        }        @Override        public long getItemId(int position) {            return position;        }        @Override        public Object getItem(int position) {            return urls.get(position);        }        @Override        public int getCount() {            return urls.size();        }        class Holder {            TextView tv_url = null;            ProgressBar progressBar = null;            TextView textView_total = null;            Button button_start = null;            Button button_pause = null;            Button button_resume = null;            Button button_delete = null;        }    };    @Override    public void onClick(View view) {        String url = view.getTag() == null ? "" : view.getTag().toString();        switch (view.getId()) {        case R.id.button_start:            downloadUtil.prepare(url);            break;        case R.id.button_pause:            downloadUtil.pause(url);            break;        case R.id.button_resume:            downloadUtil.resume(url);            break;        case R.id.button_delete:            downloadUtil.delete(url);            break;        default:            break;        }    }}

使用ListView展示待下载任务列表。使用List<String>集合urls保存下载地址。使用View.setTag(url+TAG_PROGRESS/TAG_TOTAL)的方式标记各个任务对应的View。在显示数据的时候使用findViewWithTag(url+TAG_PROGRESS/TAG_TOTAL)的方式取得对应的View；使用Timer定时器，每隔1s刷新一次下载速度。
activity_main.xml

<LinearLayout xmlns:tools="http://schemas.android.com/tools"    xmlns:android="http://schemas.android.com/apk/res/android"    android:layout_width="fill_parent"    android:layout_height="fill_parent"    android:orientation="vertical" >    <ListView         android:id="@+id/listview"        android:layout_width="match_parent"        android:layout_height="wrap_content"/></LinearLayout>

list_item.xml

<?xml version="1.0" encoding="utf-8"?><RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"    android:layout_width="match_parent"    android:layout_height="wrap_content"    android:padding="10dp" >    <TextView        android:id="@+id/url"        android:layout_width="wrap_content"        android:layout_height="wrap_content" />    <ProgressBar        android:id="@+id/progressBar"        style="?android:attr/progressBarStyleHorizontal"        android:layout_width="match_parent"        android:layout_height="wrap_content"        android:layout_below="@id/url" />    <TextView        android:id="@+id/textView_total"        android:layout_width="match_parent"        android:layout_height="wrap_content"        android:layout_below="@id/progressBar"        android:layout_margin="10dp"        android:lines="3"        android:text="下载进度" />    <LinearLayout        android:layout_width="match_parent"        android:layout_height="wrap_content"        android:layout_below="@id/textView_total" >        <Button            android:id="@+id/button_start"            android:layout_width="0dp"            android:layout_height="wrap_content"            android:layout_weight="1"            android:text="开始"            android:textSize="12sp" />        <Button            android:id="@+id/button_pause"            android:layout_width="0dp"            android:layout_height="wrap_content"            android:layout_weight="1"            android:text="暂停"            android:textSize="12sp" />        <Button            android:id="@+id/button_resume"            android:layout_width="0dp"            android:layout_height="wrap_content"            android:layout_weight="1"            android:text="继续"            android:textSize="12sp" />        <Button            android:id="@+id/button_delete"            android:layout_width="0dp"            android:layout_height="wrap_content"            android:layout_weight="1"            android:text="删除"            android:textSize="12sp" />    </LinearLayout></RelativeLayout>

最后添加连接网络和操作sdcard的权限：

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

此代码是使用数据库和RandomAccessFile类实现断点下载，除此方法外，还可以用临时文件的方式实现断点下载，具体方法：同以上代码使用HttpURLConnection和setRequestProperty方法实现文件的部分下载，然后每一部分保存为一个临时文件，待全部下载完成后，将所有相关临时文件写入到一个文件，并删除临时文件即可。