Android之断点续传下载

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类：

 1 package cn.yj3g.DBHelper;
 2
 3 import android.content.Context;
 4 import android.database.sqlite.SQLiteDatabase;
 5 import android.database.sqlite.SQLiteOpenHelper;
 6
 7     /**
 8      * 建立一个数据库帮助类
 9      */
10 public class DBHelper extends SQLiteOpenHelper {
11     //download.db-->数据库名
12     public DBHelper(Context context) {
13         super(context, "download.db", null, 1);
14     }
15
16     /**
17      * 在download.db数据库下创建一个download_info表存储下载信息
18      */
19     @Override
20     public void onCreate(SQLiteDatabase db) {
21         db.execSQL("create table download_info(_id integer PRIMARY KEY AUTOINCREMENT, thread_id integer, "
22                 + "start_pos integer, end_pos integer, compelete_size integer,url char)");
23     }
24     @Override
25     public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
26
27     }
28
29 }

下面来看主界面的布局,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：

 1 <?xml version="1.0" encoding="utf-8"?>
 2 <LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
 3     android:orientation="vertical"
 4     android:layout_width="fill_parent"
 5     android:layout_height="fill_parent"
 6     android:id="@+id/llRoot">
 7     <ListView android:id="@android:id/list"
 8         android:layout_width="fill_parent"
 9         android:layout_height="fill_parent">
10     </ListView>
11 </LinearLayout>

list_item.xml：

 1 <?xml version="1.0" encoding="utf-8"?>
 2 <LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
 3            android:orientation="vertical"
 4            android:layout_width="fill_parent"
 5            android:layout_height="wrap_content">
 6     <LinearLayout
 7            android:orientation="horizontal"
 8            android:layout_width="fill_parent"
 9            android:layout_height="wrap_content"
10            android:layout_marginBottom="5dip">
11         <TextView
12             android:layout_width="fill_parent"
13             android:layout_height="wrap_content"
14             android:layout_weight="1"
15             android:id="@+id/tv_resouce_name"/>
16         <Button
17             android:layout_width="fill_parent"
18             android:layout_height="wrap_content"
19             android:layout_weight="1"
20             android:text="下载"
21             android:id="@+id/btn_start"
22             android:onClick="startDownload"/>
23         <Button
24             android:layout_width="fill_parent"
25             android:layout_height="wrap_content"
26             android:layout_weight="1"
27             android:text="暂停"
28             android:id="@+id/btn_pause"
29             android:onClick="pauseDownload"/>
30       </LinearLayout>
31 </LinearLayout>

主界面运行效果如下：

下面我们来看具体实现下载的方法。首先，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：

 1 package cn.yj3g.entity;
 2 /**
 3  *创建一个下载信息的实体类
 4  */
 5 public class DownloadInfo {
 6     private int threadId;//下载器id
 7     private int startPos;//开始点
 8     private int endPos;//结束点
 9     private int compeleteSize;//完成度
10     private String url;//下载器网络标识
11     public DownloadInfo(int threadId, int startPos, int endPos,
12             int compeleteSize,String url) {
13         this.threadId = threadId;
14         this.startPos = startPos;
15         this.endPos = endPos;
16         this.compeleteSize = compeleteSize;
17         this.url=url;
18     }
19     public DownloadInfo() {
20     }
21     public String getUrl() {
22         return url;
23     }
24     public void setUrl(String url) {
25         this.url = url;
26     }
27     public int getThreadId() {
28         return threadId;
29     }
30     public void setThreadId(int threadId) {
31         this.threadId = threadId;
32     }
33     public int getStartPos() {
34         return startPos;
35     }
36     public void setStartPos(int startPos) {
37         this.startPos = startPos;
38     }
39     public int getEndPos() {
40         return endPos;
41     }
42     public void setEndPos(int endPos) {
43         this.endPos = endPos;
44     }
45     public int getCompeleteSize() {
46         return compeleteSize;
47     }
48     public void setCompeleteSize(int compeleteSize) {
49         this.compeleteSize = compeleteSize;
50     }
51
52     @Override
53     public String toString() {
54         return "DownloadInfo [threadId=" + threadId
55                 + ", startPos=" + startPos + ", endPos=" + endPos
56                 + ", compeleteSize=" + compeleteSize +"]";
57     }
58 }

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：

 1 package cn.yj3g.entity;
 2 /**
 3  *自定义的一个记载下载器详细信息的类
 4  */
 5 public class LoadInfo {
 6     public int fileSize;//文件大小
 7     private int complete;//完成度
 8     private String urlstring;//下载器标识
 9     public LoadInfo(int fileSize, int complete, String urlstring) {
10         this.fileSize = fileSize;
11         this.complete = complete;
12         this.urlstring = urlstring;
13     }
14     public LoadInfo() {
15     }
16     public int getFileSize() {
17         return fileSize;
18     }
19     public void setFileSize(int fileSize) {
20         this.fileSize = fileSize;
21     }
22     public int getComplete() {
23         return complete;
24     }
25     public void setComplete(int complete) {
26         this.complete = complete;
27     }
28     public String getUrlstring() {
29         return urlstring;
30     }
31     public void setUrlstring(String urlstring) {
32         this.urlstring = urlstring;
33     }
34     @Override
35     public String toString() {
36         return "LoadInfo [fileSize=" + fileSize + ", complete=" + complete
37                 + ", urlstring=" + urlstring + "]";
38     }
39 }

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，我就直接将代码附下，供大家研究参考

Downloader：

  1 package cn.yj3g.service;
  2
  3 import java.io.File;
  4 import java.io.InputStream;
  5 import java.io.RandomAccessFile;
  6 import java.net.HttpURLConnection;
  7 import java.net.URL;
  8 import java.util.ArrayList;
  9 import java.util.List;
 10 import android.content.Context;
 11 import android.os.Handler;
 12 import android.os.Message;
 13 import android.util.Log;
 14 import cn.yj3g.Dao.Dao;
 15 import cn.yj3g.entity.DownloadInfo;
 16 import cn.yj3g.entity.LoadInfo;
 17
 18 public class Downloader {
 19     private String urlstr;// 下载的地址
 20     private String localfile;// 保存路径
 21     private int threadcount;// 线程数
 22     private Handler mHandler;// 消息处理器
 23     private Dao dao;// 工具类
 24     private int fileSize;// 所要下载的文件的大小
 25     private List<DownloadInfo> infos;// 存放下载信息类的集合
 26     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
 27     private static final int DOWNLOADING = 2;
 28     private static final int PAUSE = 3;
 29     private int state = INIT;
 30
 31     public Downloader(String urlstr, String localfile, int threadcount,
 32             Context context, Handler mHandler) {
 33         this.urlstr = urlstr;
 34         this.localfile = localfile;
 35         this.threadcount = threadcount;
 36         this.mHandler = mHandler;
 37         dao = new Dao(context);
 38     }
 39     /**
 40      *判断是否正在下载
 41      */
 42     public boolean isdownloading() {
 43         return state == DOWNLOADING;
 44     }
 45     /**
 46      * 得到downloader里的信息
 47      * 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
 48      * 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
 49      */
 50     public LoadInfo getDownloaderInfors() {
 51         if (isFirst(urlstr)) {
 52             Log.v("TAG", "isFirst");
 53             init();
 54             int range = fileSize / threadcount;
 55             infos = new ArrayList<DownloadInfo>();
 56             for (int i = 0; i < threadcount - 1; i++) {
 57                 DownloadInfo info = new DownloadInfo(i, i * range, (i + 1)* range - 1, 0, urlstr);
 58                 infos.add(info);
 59             }
 60             DownloadInfo info = new DownloadInfo(threadcount - 1,(threadcount - 1) * range, fileSize - 1, 0, urlstr);
 61             infos.add(info);
 62             //保存infos中的数据到数据库
 63             dao.saveInfos(infos);
 64             //创建一个LoadInfo对象记载下载器的具体信息
 65             LoadInfo loadInfo = new LoadInfo(fileSize, 0, urlstr);
 66             return loadInfo;
 67         } else {
 68             //得到数据库中已有的urlstr的下载器的具体信息
 69             infos = dao.getInfos(urlstr);
 70             Log.v("TAG", "not isFirst size=" + infos.size());
 71             int size = 0;
 72             int compeleteSize = 0;
 73             for (DownloadInfo info : infos) {
 74                 compeleteSize += info.getCompeleteSize();
 75                 size += info.getEndPos() - info.getStartPos() + 1;
 76             }
 77             return new LoadInfo(size, compeleteSize, urlstr);
 78         }
 79     }
 80
 81     /**
 82      * 初始化
 83      */
 84     private void init() {
 85         try {
 86             URL url = new URL(urlstr);
 87             HttpURLConnection connection = (HttpURLConnection) url.openConnection();
 88             connection.setConnectTimeout(5000);
 89             connection.setRequestMethod("GET");
 90             fileSize = connection.getContentLength();
 91
 92             File file = new File(localfile);
 93             if (!file.exists()) {
 94                 file.createNewFile();
 95             }
 96             // 本地访问文件
 97             RandomAccessFile accessFile = new RandomAccessFile(file, "rwd");
 98             accessFile.setLength(fileSize);
 99             accessFile.close();
100             connection.disconnect();
101         } catch (Exception e) {
102             e.printStackTrace();
103         }
104     }
105
106     /**
107      * 判断是否是第一次 下载
108      */
109     private boolean isFirst(String urlstr) {
110         return dao.isHasInfors(urlstr);
111     }
112
113     /**
114      * 利用线程开始下载数据
115      */
116     public void download() {
117         if (infos != null) {
118             if (state == DOWNLOADING)
119                 return;
120             state = DOWNLOADING;
121             for (DownloadInfo info : infos) {
122                 new MyThread(info.getThreadId(), info.getStartPos(),
123                         info.getEndPos(), info.getCompeleteSize(),
124                         info.getUrl()).start();
125             }
126         }
127     }
128
129     public class MyThread extends Thread {
130         private int threadId;
131         private int startPos;
132         private int endPos;
133         private int compeleteSize;
134         private String urlstr;
135
136         public MyThread(int threadId, int startPos, int endPos,
137                 int compeleteSize, String urlstr) {
138             this.threadId = threadId;
139             this.startPos = startPos;
140             this.endPos = endPos;
141             this.compeleteSize = compeleteSize;
142             this.urlstr = urlstr;
143         }
144         @Override
145         public void run() {
146             HttpURLConnection connection = null;
147             RandomAccessFile randomAccessFile = null;
148             InputStream is = null;
149             try {
150                 URL url = new URL(urlstr);
151                 connection = (HttpURLConnection) url.openConnection();
152                 connection.setConnectTimeout(5000);
153                 connection.setRequestMethod("GET");
154                 // 设置范围，格式为Range：bytes x-y;
155                 connection.setRequestProperty("Range", "bytes="+(startPos + compeleteSize) + "-" + endPos);
156
157                 randomAccessFile = new RandomAccessFile(localfile, "rwd");
158                 randomAccessFile.seek(startPos + compeleteSize);
159                 // 将要下载的文件写到保存在保存路径下的文件中
160                 is = connection.getInputStream();
161                 byte[] buffer = new byte[4096];
162                 int length = -1;
163                 while ((length = is.read(buffer)) != -1) {
164                     randomAccessFile.write(buffer, 0, length);
165                     compeleteSize += length;
166                     // 更新数据库中的下载信息
167                     dao.updataInfos(threadId, compeleteSize, urlstr);
168                     // 用消息将下载信息传给进度条，对进度条进行更新
169                     Message message = Message.obtain();
170                     message.what = 1;
171                     message.obj = urlstr;
172                     message.arg1 = length;
173                     mHandler.sendMessage(message);
174                     if (state == PAUSE) {
175                         return;
176                     }
177                 }
178             } catch (Exception e) {
179                 e.printStackTrace();
180             } finally {
181                 try {
182                     is.close();
183                     randomAccessFile.close();
184                     connection.disconnect();
185                     dao.closeDb();
186                 } catch (Exception e) {
187                     e.printStackTrace();
188                 }
189             }
190
191         }
192     }
193     //删除数据库中urlstr对应的下载器信息
194     public void delete(String urlstr) {
195         dao.delete(urlstr);
196     }
197     //设置暂停
198     public void pause() {
199         state = PAUSE;
200     }
201     //重置下载状态
202     public void reset() {
203         state = INIT;
204     }
205 }

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：

 1 package cn.yj3g.Dao;
 2
 3 import java.util.ArrayList;
 4 import java.util.List;
 5 import android.content.Context;
 6 import android.database.Cursor;
 7 import android.database.sqlite.SQLiteDatabase;
 8 import cn.yj3g.DBHelper.DBHelper;
 9 import cn.yj3g.entity.DownloadInfo;
10
11 /**
12  *
13  * 一个业务类
14  */
15 public class Dao {
16     private DBHelper dbHelper;
17
18     public Dao(Context context) {
19         dbHelper = new DBHelper(context);
20     }
21
22     /**
23      * 查看数据库中是否有数据
24      */
25     public boolean isHasInfors(String urlstr) {
26         SQLiteDatabase database = dbHelper.getReadableDatabase();
27         String sql = "select count(*)  from download_info where url=?";
28         Cursor cursor = database.rawQuery(sql, new String[] { urlstr });
29         cursor.moveToFirst();
30         int count = cursor.getInt(0);
31         cursor.close();
32         return count == 0;
33     }
34
35     /**
36      * 保存 下载的具体信息
37      */
38     public void saveInfos(List<DownloadInfo> infos) {
39         SQLiteDatabase database = dbHelper.getWritableDatabase();
40         for (DownloadInfo info : infos) {
41             String sql = "insert into download_info(thread_id,start_pos, end_pos,compelete_size,url) values (?,?,?,?,?)";
42             Object[] bindArgs = { info.getThreadId(), info.getStartPos(),
43                     info.getEndPos(), info.getCompeleteSize(), info.getUrl() };
44             database.execSQL(sql, bindArgs);
45         }
46     }
47
48     /**
49      * 得到下载具体信息
50      */
51     public List<DownloadInfo> getInfos(String urlstr) {
52         List<DownloadInfo> list = new ArrayList<DownloadInfo>();
53         SQLiteDatabase database = dbHelper.getReadableDatabase();
54         String sql = "select thread_id, start_pos, end_pos,compelete_size,url from download_info where url=?";
55         Cursor cursor = database.rawQuery(sql, new String[] { urlstr });
56         while (cursor.moveToNext()) {
57             DownloadInfo info = new DownloadInfo(cursor.getInt(0),
58                     cursor.getInt(1), cursor.getInt(2), cursor.getInt(3),
59                     cursor.getString(4));
60             list.add(info);
61         }
62         cursor.close();
63         return list;
64     }
65
66     /**
67      * 更新数据库中的下载信息
68      */
69     public void updataInfos(int threadId, int compeleteSize, String urlstr) {
70         SQLiteDatabase database = dbHelper.getReadableDatabase();
71         String sql = "update download_info set compelete_size=? where thread_id=? and url=?";
72         Object[] bindArgs = { compeleteSize, threadId, urlstr };
73         database.execSQL(sql, bindArgs);
74     }
75     /**
76      * 关闭数据库
77      */
78     public void closeDb() {
79         dbHelper.close();
80     }
81
82     /**
83      * 下载完成后删除数据库中的数据
84      */
85     public void delete(String url) {
86         SQLiteDatabase database = dbHelper.getReadableDatabase();
87         database.delete("download_info", "url=?", new String[] { url });
88         database.close();
89     }
90 }

下来就是要进行下载和暂停按钮的响应事件了。具体代码和解释如下。

MainActivity：

  1 package cn.yj3g.AndroidDownload;
  2
  3 import java.util.ArrayList;
  4 import java.util.HashMap;
  5 import java.util.List;
  6 import java.util.Map;
  7 import android.app.ListActivity;
  8 import android.os.Bundle;
  9 import android.os.Handler;
 10 import android.os.Message;
 11 import android.view.View;
 12 import android.widget.LinearLayout;
 13 import android.widget.LinearLayout.LayoutParams;
 14 import android.widget.ProgressBar;
 15 import android.widget.SimpleAdapter;
 16 import android.widget.TextView;
 17 import android.widget.Toast;
 18 import cn.yj3g.entity.LoadInfo;
 19 import cn.yj3g.service.Downloader;
 20
 21 public class MainActivity extends ListActivity {
 22     // 固定下载的资源路径，这里可以设置网络上的地址
 23     private static final String URL = "http://192.168.1.105:8080/struts2_net/";
 24     // 固定存放下载的音乐的路径：SD卡目录下
 25     private static final String SD_PATH = "/mnt/sdcard/";
 26     // 存放各个下载器
 27     private Map<String, Downloader> downloaders = new HashMap<String, Downloader>();
 28     // 存放与下载器对应的进度条
 29     private Map<String, ProgressBar> ProgressBars = new HashMap<String, ProgressBar>();
 30     /**
 31      * 利用消息处理机制适时更新进度条
 32      */
 33     private Handler mHandler = new Handler() {
 34         public void handleMessage(Message msg) {
 35             if (msg.what == 1) {
 36                 String url = (String) msg.obj;
 37                 int length = msg.arg1;
 38                 ProgressBar bar = ProgressBars.get(url);
 39                 if (bar != null) {
 40                     // 设置进度条按读取的length长度更新
 41                     bar.incrementProgressBy(length);
 42                     if (bar.getProgress() == bar.getMax()) {
 43                         Toast.makeText(MainActivity.this, "下载完成！", 0).show();
 44                         // 下载完成后清除进度条并将map中的数据清空
 45                         LinearLayout layout = (LinearLayout) bar.getParent();
 46                         layout.removeView(bar);
 47                         ProgressBars.remove(url);
 48                         downloaders.get(url).delete(url);
 49                         downloaders.get(url).reset();
 50                         downloaders.remove(url);
 51
 52                     }
 53                 }
 54             }
 55         }
 56     };
 57     @Override
 58     public void onCreate(Bundle savedInstanceState) {
 59         super.onCreate(savedInstanceState);
 60         setContentView(R.layout.main);
 61         showListView();
 62     }
 63     // 显示listView，这里可以随便添加音乐
 64     private void showListView() {
 65         List<Map<String, String>> data = new ArrayList<Map<String, String>>();
 66         Map<String, String> map = new HashMap<String, String>();
 67         map.put("name", "mm.mp3");
 68         data.add(map);
 69         map = new HashMap<String, String>();
 70         map.put("name", "pp.mp3");
 71         data.add(map);
 72         map = new HashMap<String, String>();
 73         map.put("name", "tt.mp3");
 74         data.add(map);
 75         map = new HashMap<String, String>();
 76         map.put("name", "You.mp3");
 77         data.add(map);
 78         SimpleAdapter adapter = new SimpleAdapter(this, data, R.layout.list_item, new String[] { "name" },
 79                 new int[] { R.id.tv_resouce_name });
 80         setListAdapter(adapter);
 81     }
 82     /**
 83      * 响应开始下载按钮的点击事件
 84      */
 85     public void startDownload(View v) {
 86         // 得到textView的内容
 87         LinearLayout layout = (LinearLayout) v.getParent();
 88         String musicName = ((TextView) layout.findViewById(R.id.tv_resouce_name)).getText().toString();
 89         String urlstr = URL + musicName;
 90         String localfile = SD_PATH + musicName;
 91         //设置下载线程数为4，这里是我为了方便随便固定的
 92         int threadcount = 4;
 93         // 初始化一个downloader下载器
 94         Downloader downloader = downloaders.get(urlstr);
 95         if (downloader == null) {
 96             downloader = new Downloader(urlstr, localfile, threadcount, this, mHandler);
 97             downloaders.put(urlstr, downloader);
 98         }
 99         if (downloader.isdownloading())
100             return;
101         // 得到下载信息类的个数组成集合
102         LoadInfo loadInfo = downloader.getDownloaderInfors();
103         // 显示进度条
104         showProgress(loadInfo, urlstr, v);
105         // 调用方法开始下载
106         downloader.download();
107     }
108
109     /**
110      * 显示进度条
111      */
112     private void showProgress(LoadInfo loadInfo, String url, View v) {
113         ProgressBar bar = ProgressBars.get(url);
114         if (bar == null) {
115             bar = new ProgressBar(this, null, android.R.attr.progressBarStyleHorizontal);
116             bar.setMax(loadInfo.getFileSize());
117             bar.setProgress(loadInfo.getComplete());
118             ProgressBars.put(url, bar);
119             LinearLayout.LayoutParams params = new LayoutParams(LayoutParams.FILL_PARENT, 5);
120             ((LinearLayout) ((LinearLayout) v.getParent()).getParent()).addView(bar, params);
121         }
122     }
123     /**
124      * 响应暂停下载按钮的点击事件
125      */
126     public void pauseDownload(View v) {
127         LinearLayout layout = (LinearLayout) v.getParent();
128         String musicName = ((TextView) layout.findViewById(R.id.tv_resouce_name)).getText().toString();
129         String urlstr = URL + musicName;
130         downloaders.get(urlstr).pause();
131     }
132 }

最后我们要在清单文件中添加权限，一个是访问网络的权限，一个是往SD卡写数据的权限。代码如下：

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

这样我们就实现了文件的断点续传下载功能。具体效果图如下：