[Android实例] Android之断点续传下载

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

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

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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：

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

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list_item.xml：

1. <LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
2. android:layout_height="fill_parent" android:id="@+id/linearLayout1"
3. android:layout_width="fill_parent" android:orientation="vertical">
4. <LinearLayout android:layout_width="fill_parent"
5. android:id="@+id/linearLayout2" android:layout_height="wrap_content"
6. android:orientation="horizontal" android:layout_marginBottom="5dip">
7. <TextView android:layout_width="fill_parent"
8. android:layout_height="wrap_content" android:layout_weight="1"
9. android:id="@+id/tv_resouce_name" />
10. <Button android:layout_width="fill_parent"
11. android:layout_height="wrap_content" android:layout_weight="1"
12. android:text="下载" android:id="@+id/btn_start" android:onClick="startDownload" />
13. <Button android:layout_width="fill_parent"
14. android:layout_height="wrap_content" android:layout_weight="1"
15. android:text="暂停" android:id="@+id/btn_pause" android:onClick="pauseDownload" />
16. </LinearLayout>
17. </LinearLayout>

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

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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 com.icss.entity;
2. public class LoadInfo {
3. public int fileSize;// 文件大小
4. private int complete;// 完成度
5. private String urlstring;// 下载器标识
6. public LoadInfo() {
7. super();
8. // TODO Auto-generated constructor stub
9. }
10. public LoadInfo(int fileSize, int complete, String urlstring) {
11. super();
12. this.fileSize = fileSize;
13. this.complete = complete;
14. this.urlstring = urlstring;
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. }

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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:

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

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

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下面的是程序的主程序，其他的不说了，直接上代码：

1. package com.icss;
2. import java.util.ArrayList;
3. import java.util.HashMap;
4. import java.util.List;
5. import java.util.Map;
6. import android.app.ListActivity;
7. import android.os.Bundle;
8. import android.os.Handler;
9. import android.os.Message;
10. import android.view.View;
11. import android.widget.LinearLayout;
12. import android.widget.LinearLayout.LayoutParams;
13. import android.widget.ProgressBar;
14. import android.widget.SimpleAdapter;
15. import android.widget.TextView;
16. import android.widget.Toast;
17. import com.icss.entity.LoadInfo;
18. import com.icss.service.Downloader;
19. public class MainActivity extends ListActivity {
20. // 固定下载的资源路径，这里可以设置网络上的地址
21. private static final String URL = "http://10.0.0.80:8080/xiangce/";
22. // 固定存放下载的音乐的路径：SD卡目录下
23. private static final String SD_PATH = "/mnt/sdcard/";
24. // 存放各个下载器
25. private Map<String, Downloader> downloaders = new HashMap<String, Downloader>();
26. // 存放与下载器对应的进度条
27. private Map<String, ProgressBar> ProgressBars = new HashMap<String, ProgressBar>();
28. /**
29. * 31 * 利用消息处理机制适时更新进度条 32
30. */
31. private Handler mHandler = new Handler() {
32. public void handleMessage(Message msg) {
33. if (msg.what == 1) {
34. String url = (String) msg.obj;
35. int length = msg.arg1;
36. ProgressBar bar = ProgressBars.get(url);
37. if (bar != null) {
38. // 设置进度条按读取的length长度更新
39. bar.incrementProgressBy(length);
40. if (bar.getProgress() == bar.getMax()) {
41. Toast.makeText(MainActivity.this, "下载完成！", 0).show();
42. // 下载完成后清除进度条并将map中的数据清空
43. LinearLayout layout = (LinearLayout) bar.getParent();
44. layout.removeView(bar);
45. ProgressBars.remove(url);
46. downloaders.get(url).delete(url);
47. downloaders.get(url).reset();
48. downloaders.remove(url);
49. }
50. }
51. }
52. }
53. };
54. @Override
55. public void onCreate(Bundle savedInstanceState) {
56. super.onCreate(savedInstanceState);
57. setContentView(R.layout.main);
58. showListView();
59. }
60. // 显示listView，这里可以随便添加音乐
61. private void showListView() {
62. List<Map<String, String>> data = new ArrayList<Map<String, String>>();
63. Map<String, String> map = new HashMap<String, String>();
64. map.put("name", "mm.mp3");
65. data.add(map);
66. map = new HashMap<String, String>();
67. map.put("name", "pp.mp3");
68. data.add(map);
69. map = new HashMap<String, String>();
70. map.put("name", "tt.mp3");
71. data.add(map);
72. map = new HashMap<String, String>();
73. map.put("name", "You.mp3");
74. data.add(map);
75. SimpleAdapter adapter = new SimpleAdapter(this, data,
76. R.layout.list_item, new String[] { "name" },
77. new int[] { R.id.tv_resouce_name });
78. setListAdapter(adapter);
79. }
80. /**
81. * 83 * 响应开始下载按钮的点击事件 84
82. */
83. public void startDownload(View v) {
84. // 得到textView的内容
85. LinearLayout layout = (LinearLayout) v.getParent();
86. String musicName = ((TextView) layout
87. .findViewById(R.id.tv_resouce_name)).getText().toString();
88. String urlstr = URL + musicName;
89. String localfile = SD_PATH + musicName;
90. // 设置下载线程数为4，这里是我为了方便随便固定的
91. int threadcount = 4;
92. // 初始化一个downloader下载器
93. Downloader downloader = downloaders.get(urlstr);
94. if (downloader == null) {
95. downloader = new Downloader(urlstr, localfile, threadcount, this,
96. 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. * 显示进度条
110. */
111. private void showProgress(LoadInfo loadInfo, String url, View v) {
112. ProgressBar bar = ProgressBars.get(url);
113. if (bar == null) {
114. bar = new ProgressBar(this, null,
115. android.R.attr.progressBarStyleHorizontal);
116. bar.setMax(loadInfo.getFileSize());
117. bar.setProgress(loadInfo.getComplete());
118. System.out.println(loadInfo.getFileSize()+"--"+loadInfo.getComplete());
119. ProgressBars.put(url, bar);
120. LinearLayout.LayoutParams params = new LayoutParams(
121. LayoutParams.FILL_PARENT, 5);
122. ((LinearLayout) ((LinearLayout) v.getParent()).getParent())
123. .addView(bar, params);
124. }
125. }
126. /**
127. * 响应暂停下载按钮的点击事件
128. */
129. public void pauseDownload(View v) {
130. LinearLayout layout = (LinearLayout) v.getParent();
131. String musicName = ((TextView) layout
132. .findViewById(R.id.tv_resouce_name)).getText().toString();
133. String urlstr = URL + musicName;
134. downloaders.get(urlstr).pause();
135. }
136. }

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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。

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

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最后运行的效果图：

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！