Android之断点续传下载（转）

 

原文链接

    在我们做开发的时候经常遇到的就是下载了，现在下载的方法有很多很多，那么怎么做到断点续传下载呢！很多人都头疼这个问题，如果我们没有很好的逻辑真不是很容易解决啊。我参考了一下前辈们的资料了整理了一个项目，能实现多个文件的同时下载。
     断点续传下载，顾名思义，那就是我们在一次下载未结束时，退出下载，第二次下载时会接着第一次下载的进度继续下载。那么怎么记录第一次下载的数据呢，这里肯定就要用到数据库了。下面就是我创建数据库的一个SQLiteOpenHelper类。用来首次运行时创建数据库。
DBHelper.java

package com.icss.DBHelper;

import android.content.Context;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteOpenHelper;

/**
 * 建立一个数据库帮助类
 */
public class DBHelper extends SQLiteOpenHelper {
        // download.db-->数据库名
        public DBHelper(Context context) {
                super(context, "download.db", null, 1);
        }

        /**
         * 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) {

        }

}

 下面看主界面的布局,在这里，我只设计了一个ListView来显示下载的音乐的名称，和一个开始下载按钮和一个暂停按钮。
布局文件如下：
main.xml：

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
        android:orientation="vertical" android:layout_width="fill_parent"
        android:layout_height="fill_parent" android:weightSum="1">
        <ListView android:id="@android:id/list" android:layout_height="wrap_content"
                android:layout_width="match_parent" android:layout_weight="0.70"></ListView>
</LinearLayout>

 list_item.xml：

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
        android:layout_height="fill_parent" android:id="@+id/linearLayout1"
        android:layout_width="fill_parent" android:orientation="vertical">
        <LinearLayout android:layout_width="fill_parent"
                android:id="@+id/linearLayout2" android:layout_height="wrap_content"
                android:orientation="horizontal" android:layout_marginBottom="5dip">
                <TextView android:layout_width="fill_parent"
                        android:layout_height="wrap_content" android:layout_weight="1"
                        android:id="@+id/tv_resouce_name" />
                <Button android:layout_width="fill_parent"
                        android:layout_height="wrap_content" android:layout_weight="1"
                        android:text="下载" android:id="@+id/btn_start" android:onClick="startDownload" />
                <Button android:layout_width="fill_parent"
                        android:layout_height="wrap_content" android:layout_weight="1"
                        android:text="暂停" android:id="@+id/btn_pause" android:onClick="pauseDownload" />
        </LinearLayout>
</LinearLayout>

     我们要定义一个记录在下载时各个时期的数据的类，这里我创建了一个DownloadInfo类来记录。代码如下：
DownloadInfo：

package com.icss.entity;

public class DownloadInfo {

        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;// 下载器网络标识
        
        
        
        public DownloadInfo(int threadId, int startPos, int endPos,
                        int compeleteSize, String url) {
                super();
                this.threadId = threadId;
                this.startPos = startPos;
                this.endPos = endPos;
                this.compeleteSize = compeleteSize;
                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;
        }
        public String getUrl() {
                return url;
        }
        public void setUrl(String url) {
                this.url = url;
        }
        
        @Override
             public String toString() {
                 return "DownloadInfo [threadId=" + threadId
                         + ", startPos=" + startPos + ", endPos=" + endPos
                         + ", compeleteSize=" + compeleteSize +"]";
     }


}

     在下载时，我们有进度条来显示进度，怎么确定进度条的进度，大小和起始位置呢？这里我定义了一个LoadInfo类来记录下载器详细信息。代码如下：

LoadInfo：

package com.icss.entity;

public class LoadInfo {

        public int fileSize;// 文件大小
        private int complete;// 完成度
        private String urlstring;// 下载器标识
        public LoadInfo() {
                super();
                // TODO Auto-generated constructor stub
        }
        public LoadInfo(int fileSize, int complete, String urlstring) {
                super();
                this.fileSize = fileSize;
                this.complete = complete;
                this.urlstring = urlstring;
        }
        public int getFileSize() {
                return fileSize;
        }
        public void setFileSize(int fileSize) {
                this.fileSize = fileSize;
        }
        public int getComplete() {
                return complete;
        }
        public void setComplete(int complete) {
                this.complete = complete;
        }
        public String getUrlstring() {
                return urlstring;
        }
        public void setUrlstring(String urlstring) {
                this.urlstring = urlstring;
        }
        @Override
            public String toString() {
         return "LoadInfo [fileSize=" + fileSize + ", complete=" + complete
                         + ", urlstring=" + urlstring + "]";
     }


}

    下面是最最重要的一步，那就是定义一个下载器来进行下载了，这里我就不多说，具体解释在代码中都有注解，供大家研究参考。
Downloader:

package com.icss.service;

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 com.icss.dao.Dao;
import com.icss.entity.DownloadInfo;
import com.icss.entity.LoadInfo;

import android.content.Context;
import android.os.Handler;
import android.os.Message;
import android.util.Log;

public class Downloader {
        private String urlstr;// 下载的地址
        private String localfile;// 保存路径
        private int threadcount;// 线程数
        private Handler mHandler;// 消息处理器
        private Dao dao;// 工具类
        private int fileSize;// 所要下载的文件的大小
        private List<DownloadInfo> infos;// 存放下载信息类的集合
        private static final int INIT = 1;// 定义三种下载的状态：初始化状态，正在下载状态，暂停状态
        private static final int DOWNLOADING = 2;
        private static final int PAUSE = 3;
        private int state = INIT;

        public Downloader(String urlstr, String localfile, int threadcount,
                        Context context, Handler mHandler) {
                this.urlstr = urlstr;
                this.localfile = localfile;
                this.threadcount = threadcount;
                this.mHandler = mHandler;
                dao = new Dao(context);
        }

        /**
         * 判断是否正在下载
         */
        public boolean isdownloading() {
                return state == DOWNLOADING;
        }

        /**
         * 得到downloader里的信息 首先进行判断是否是第一次下载，如果是第一次就要进行初始化，并将下载器的信息保存到数据库中
         * 如果不是第一次下载，那就要从数据库中读出之前下载的信息（起始位置，结束为止，文件大小等），并将下载信息返回给下载器
         */
        public LoadInfo getDownloaderInfors() {
                if (isFirst(urlstr)) {
                        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, urlstr);
                                infos.add(info);
                        }
                        DownloadInfo info = new DownloadInfo(threadcount - 1,
                                        (threadcount - 1) * range, fileSize - 1, 0, urlstr);
                        infos.add(info);
                        // 保存infos中的数据到数据库
                        dao.saveInfos(infos);
                        // 创建一个LoadInfo对象记载下载器的具体信息
                        LoadInfo loadInfo = new LoadInfo(fileSize, 0, urlstr);
                        return loadInfo;
                } else {
                        // 得到数据库中已有的urlstr的下载器的具体信息
                        infos = dao.getInfos(urlstr);
                        Log.v("TAG", "not isFirst size=" + infos.size());
                        int size = 0;
                        int compeleteSize = 0;
                        for (DownloadInfo info : infos) {
                                compeleteSize += info.getCompeleteSize();
                                size += info.getEndPos() - info.getStartPos() + 1;
                        }
                        return new LoadInfo(size, compeleteSize, urlstr);
                }
        }

        /**
      */
        private void init() {
                try {
                        URL url = new URL(urlstr);
                        HttpURLConnection connection = (HttpURLConnection) url
                                        .openConnection();
                        connection.setConnectTimeout(5000);
                        connection.setRequestMethod("GET");
                        fileSize = connection.getContentLength();
                        File file = new File(localfile);
                        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();
                }
        }

        /**
         * 判断是否是第一次 下载
         */
        private boolean isFirst(String urlstr) {
                return dao.isHasInfors(urlstr);
        }

        /**
         * 114 * 利用线程开始下载数据 115
         */
        public void download() {
                if (infos != null) {
                        if (state == DOWNLOADING)
                                return;
                        state = DOWNLOADING;
                        for (DownloadInfo info : infos) {
                                new MyThread(info.getThreadId(), info.getStartPos(),
                                                info.getEndPos(), info.getCompeleteSize(),
                                                info.getUrl()).start();
                        }
                }
        }

        public class MyThread extends Thread {
                private int threadId;
                private int startPos;
                private int endPos;
                private int compeleteSize;
                private String urlstr;

                public MyThread(int threadId, int startPos, int endPos,
                                int compeleteSize, String urlstr) {
                        this.threadId = threadId;
                        this.startPos = startPos;
                        this.endPos = endPos;
                        this.compeleteSize = compeleteSize;
                        this.urlstr = urlstr;
                }

                @Override
                public void run() {
                        HttpURLConnection connection = null;
                        RandomAccessFile randomAccessFile = null;
                        InputStream is = null;
                        try {
                                URL url = new URL(urlstr);
                                connection = (HttpURLConnection) url.openConnection();
                                connection.setConnectTimeout(5000);
                                connection.setRequestMethod("GET");
                                // 设置范围，格式为Range：bytes x-y;
                                connection.setRequestProperty("Range", "bytes="
                                                + (startPos + compeleteSize) + "-" + endPos);

                                randomAccessFile = new RandomAccessFile(localfile, "rwd");
                                randomAccessFile.seek(startPos + compeleteSize);
                                // 将要下载的文件写到保存在保存路径下的文件中
                                is = connection.getInputStream();
                                byte[] buffer = new byte[4096];
                                int length = -1;
                                while ((length = is.read(buffer)) != -1) {
                                        randomAccessFile.write(buffer, 0, length);
                                        compeleteSize += length;
                                        // 更新数据库中的下载信息
                                        dao.updataInfos(threadId, compeleteSize, urlstr);
                                        // 用消息将下载信息传给进度条，对进度条进行更新
                                        Message message = Message.obtain();
                                        message.what = 1;
                                        message.obj = urlstr;
                                        message.arg1 = length;
                                        mHandler.sendMessage(message);
                                        if (state == PAUSE) {
                                                return;
                                        }
                                }
                        } catch (Exception e) {
                                e.printStackTrace();
                        } finally {
                                try {
                                        is.close();
                                        randomAccessFile.close();
                                        connection.disconnect();
                                        dao.closeDb();
                                } catch (Exception e) {
                                        e.printStackTrace();
                                }
                        }

                }
        }

        // 删除数据库中urlstr对应的下载器信息
        public void delete(String urlstr) {
                dao.delete(urlstr);
        }

        // 设置暂停
        public void pause() {
                state = PAUSE;
        }

        // 重置下载状态
        public void reset() {
                state = INIT;
        }
}

     在这边下载器类的定义中，我们用到了许多关于进行数据库操作的方法，这里我定义了一个数据库工具类，来提供这些方法，代码如下：
Dao：

package com.icss.dao;

import java.util.ArrayList;
import java.util.List;
import javax.crypto.spec.DESKeySpec;

import com.icss.DBHelper.DBHelper;
import com.icss.entity.DownloadInfo;

 import android.content.Context;
 import android.database.Cursor;
import android.database.sqlite.SQLiteDatabase;


 /**
  *
  * 一个业务类
  */
 public class Dao {
     private DBHelper dbHelper;

     public Dao(Context context) {
         dbHelper = new DBHelper(context);
         
     }

     /**
      * 查看数据库中是否有数据
      */
     public boolean isHasInfors(String urlstr) {
         SQLiteDatabase database = dbHelper.getReadableDatabase();
        String sql = "select count(*)  from download_info where url=?";
         Cursor cursor = database.rawQuery(sql, new String[] { urlstr });
         cursor.moveToFirst();
         int count = cursor.getInt(0);
        cursor.close();
         return count == 0;
     }

     /**
      * 保存 下载的具体信息
      */
     public void saveInfos(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.getReadableDatabase();
         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.getReadableDatabase();
         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.getReadableDatabase();
         database.delete("download_info", "url=?", new String[] { url });
         database.close();
     }
 }

 下面的是程序的主程序，其他的不说了，直接上代码：

package com.icss;

import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import java.util.Map;

import android.app.ListActivity;
import android.os.Bundle;
import android.os.Handler;
import android.os.Message;
import android.view.View;
import android.widget.LinearLayout;
import android.widget.LinearLayout.LayoutParams;
import android.widget.ProgressBar;
import android.widget.SimpleAdapter;
import android.widget.TextView;
import android.widget.Toast;

import com.icss.entity.LoadInfo;
import com.icss.service.Downloader;

public class MainActivity extends ListActivity {
        // 固定下载的资源路径，这里可以设置网络上的地址
        private static final String URL = "http://10.0.0.80:8080/xiangce/";
        // 固定存放下载的音乐的路径：SD卡目录下
        private static final String SD_PATH = "/mnt/sdcard/";
        // 存放各个下载器
        private Map<String, Downloader> downloaders = new HashMap<String, Downloader>();
        // 存放与下载器对应的进度条
        private Map<String, ProgressBar> ProgressBars = new HashMap<String, ProgressBar>();
        /**
         * 31 * 利用消息处理机制适时更新进度条 32
         */
        private Handler mHandler = new Handler() {
                public void handleMessage(Message msg) {
                        if (msg.what == 1) {
                                String url = (String) msg.obj;
                                int length = msg.arg1;
                                ProgressBar bar = ProgressBars.get(url);
                                if (bar != null) {
                                        // 设置进度条按读取的length长度更新
                                        bar.incrementProgressBy(length);
                                        if (bar.getProgress() == bar.getMax()) {
                                                Toast.makeText(MainActivity.this, "下载完成！", 0).show();
                                                // 下载完成后清除进度条并将map中的数据清空
                                                LinearLayout layout = (LinearLayout) bar.getParent();
                                                layout.removeView(bar);
                                                ProgressBars.remove(url);
                                                downloaders.get(url).delete(url);
                                                downloaders.get(url).reset();
                                                downloaders.remove(url);

                                        }
                                }
                        }
                }
        };

        @Override
        public void onCreate(Bundle savedInstanceState) {
                super.onCreate(savedInstanceState);
                setContentView(R.layout.main);
                showListView();
        }

        // 显示listView，这里可以随便添加音乐
        private void showListView() {
                List<Map<String, String>> data = new ArrayList<Map<String, String>>();
                Map<String, String> map = new HashMap<String, String>();
                map.put("name", "mm.mp3");
                data.add(map);
                map = new HashMap<String, String>();
                map.put("name", "pp.mp3");
                data.add(map);
                map = new HashMap<String, String>();
                map.put("name", "tt.mp3");
                data.add(map);
                map = new HashMap<String, String>();
                map.put("name", "You.mp3");
                data.add(map);
                SimpleAdapter adapter = new SimpleAdapter(this, data,
                                R.layout.list_item, new String[] { "name" },
                                new int[] { R.id.tv_resouce_name });
                setListAdapter(adapter);
        }

        /**
         * 83 * 响应开始下载按钮的点击事件 84
         */
        public void startDownload(View v) {
                // 得到textView的内容
                LinearLayout layout = (LinearLayout) v.getParent();
                String musicName = ((TextView) layout
                                .findViewById(R.id.tv_resouce_name)).getText().toString();
                String urlstr = URL + musicName;
                String localfile = SD_PATH + musicName;
                // 设置下载线程数为4，这里是我为了方便随便固定的
                int threadcount = 4;
                // 初始化一个downloader下载器
                Downloader downloader = downloaders.get(urlstr);
                if (downloader == null) {
                        downloader = new Downloader(urlstr, localfile, threadcount, this,
                                        mHandler);
                        downloaders.put(urlstr, downloader);
                }
                if (downloader.isdownloading())
                        return;
                // 得到下载信息类的个数组成集合
                LoadInfo loadInfo = downloader.getDownloaderInfors();
                // 显示进度条
                showProgress(loadInfo, urlstr, v);
                // 调用方法开始下载
                downloader.download();
        }

        /**
         * 显示进度条
         */
        private void showProgress(LoadInfo loadInfo, String url, View v) {
                ProgressBar bar = ProgressBars.get(url);
                if (bar == null) {
                        bar = new ProgressBar(this, null,
                                        android.R.attr.progressBarStyleHorizontal);
                        bar.setMax(loadInfo.getFileSize());
                        bar.setProgress(loadInfo.getComplete());
                        System.out.println(loadInfo.getFileSize()+"--"+loadInfo.getComplete());
                        ProgressBars.put(url, bar);
                        LinearLayout.LayoutParams params = new LayoutParams(
                                        LayoutParams.FILL_PARENT, 5);
                        ((LinearLayout) ((LinearLayout) v.getParent()).getParent())
                                        .addView(bar, params);
                }
        }

        /**
         * 响应暂停下载按钮的点击事件
         */
        public void pauseDownload(View v) {
                LinearLayout layout = (LinearLayout) v.getParent();
                String musicName = ((TextView) layout
                                .findViewById(R.id.tv_resouce_name)).getText().toString();
                String urlstr = URL + musicName;
                downloaders.get(urlstr).pause();
        }
}

     最后我们需要在android Manifest.xml中添加这两个权限一个是访问internet的权限，另一个是写外存的权限。

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

     万事俱备只欠东风啦！哈哈，我需要在我的web工程里放几个音乐文件。

    下载后得到的文件可在sdcard下面找到！