Android网络多线程断点续传下载

本示例介绍在Android平台下通过HTTP协议实现断点续传下载。

我们编写的是Andorid的HTTP协议多线程断点下载应用程序。直接使用单线程下载HTTP文件对我们来说是一件非常简单的事。那么，多线程断点需要什么功能？难在哪里？

1.多线程下载，

2.支持断点。

 

使用多线程的好处：使用多线程下载会提升文件下载的速度。那么多线程下载文件的过程是：

(1)首先获得下载文件的长度，然后设置本地文件的长度。

HttpURLConnection.getContentLength();//获取下载文件的长度

RandomAccessFile file = new RandomAccessFile("QQWubiSetup.exe","rwd");

file.setLength(filesize);//设置本地文件的长度

          (2)根据文件长度和线程数计算每条线程下载的数据长度和下载位置。

             如：文件的长度为6M，线程数为3，那么，每条线程下载的数据长度为2M，每条线程开始下载的位置如下图所示。

           例如10M大小，使用3个线程来下载，

               线程下载的数据长度   (10%3 == 0 ？ 10/3:10/3+1) ,第1，2个线程下载长度是4M，第三个线程下载长度为2M

                下载开始位置：线程id*每条线程下载的数据长度 = ?

下载结束位置：（线程id+1）*每条线程下载的数据长度-1=?

          (3)使用Http的Range头字段指定每条线程从文件的什么位置开始下载，下载到什么位置为止，

                如：指定从文件的2M位置开始下载，下载到位置(4M-1byte)为止

           代码如下：HttpURLConnection.setRequestProperty("Range", "bytes=2097152-4194303");

          (4)保存文件，使用RandomAccessFile类指定每条线程从本地文件的什么位置开始写入数据。

RandomAccessFile threadfile = new RandomAccessFile("QQWubiSetup.exe ","rwd");

threadfile.seek(2097152);//从文件的什么位置开始写入数据

程序结构如下图所示：

string.xml文件中代码：

1. <?xml version="1.0" encoding="utf-8"?>
2. <resources>
3. <string name="hello">Hello World, MainActivity!</string>
4. <string name="app_name">Android网络多线程断点下载</string>
5. <string name="path">下载路径</string>
6. <string name="downloadbutton">下载</string>
7. <string name="sdcarderror">SDCard不存在或者写保护</string>
8. <string name="success">下载完成</string>
9. <string name="error">下载失败</string>
10. </resources>

main.xml文件中代码：

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. <!-- 下载路径 -->
7. <TextView
8. android:layout_width="fill_parent"
9. android:layout_height="wrap_content"
10. android:text="@string/path"/>
11. <EditText
12. android:id="@+id/path"
13. android:text="http://www.winrar.com.cn/download/wrar380sc.exe"
14. android:layout_width="fill_parent"
15. android:layout_height="wrap_content">
16. </EditText>
17. <!-- 下载按钮 -->
18. <Button
19. android:layout_width="wrap_content"
20. android:layout_height="wrap_content"
21. android:text="@string/downloadbutton"
22. android:id="@+id/button"/>
23. <!-- 进度条 -->
24. <ProgressBar
25. android:layout_width="fill_parent"
26. android:layout_height="20dip"
27. style="?android:attr/progressBarStyleHorizontal"
28. android:id="@+id/downloadbar" />
29. <TextView
30. android:layout_width="fill_parent"
31. android:layout_height="wrap_content"
32. android:gravity="center"
33. android:id="@+id/resultView" />
34. </LinearLayout>

  AndroidManifest.xml文件中代码：

1. <?xml version="1.0" encoding="utf-8"?>
2. <manifest
   xmlns:android="http://schemas.android.com/apk/res/android"    
    package="com.android.downloader"      android:versionCode="1"    
    android:versionName="1.0">
3. <uses-sdk android:minSdkVersion="8" />
4. <application android:icon="@drawable/icon" android:label="@string/app_name">
5. <activity android:name=".MainActivity"
6. android:label="@string/app_name">
7. <intent-filter>
8. <action android:name="android.intent.action.MAIN" />
9. <category android:name="android.intent.category.LAUNCHER" />
10. </intent-filter>
11. </activity>
12. </application>
13. <!-- 在SDCard中创建与删除文件权限 -->
14. <uses-permission android:name="android.permission.MOUNT_UNMOUNT_FILESYSTEMS"/>
15. <!-- 往SDCard写入数据权限 -->
16. <uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE"/>
17. <!-- 访问internet权限 -->
18. <uses-permission android:name="android.permission.INTERNET"/>
19. </manifest>

MainActivity中代码：

1. package com.android.downloader;
2. import java.io.File;
3. import com.android.network.DownloadProgressListener;
4. import com.android.network.FileDownloader;
5. import android.app.Activity;
6. import android.os.Bundle;
7. import android.os.Environment;
8. import android.os.Handler;
9. import android.os.Message;
10. import android.view.View;
11. import android.widget.Button;
12. import android.widget.EditText;
13. import android.widget.ProgressBar;
14. import android.widget.TextView;
15. import android.widget.Toast;
16. public class MainActivity extends Activity {
17. private EditText downloadpathText;
18. private TextView resultView;
19. private ProgressBar progressBar;
20. /**
21. * 当Handler被创建会关联到创建它的当前线程的消息队列，该类用于往消息队列发送消息
22. * 消息队列中的消息由当前线程内部进行处理
23. */
24. private Handler handler = new Handler(){
25. @Override
26. public void handleMessage(Message msg) {
27. switch (msg.what) {
28. case 1:
29. progressBar.setProgress(msg.getData().getInt("size"));
30. float num = (float)progressBar.getProgress()/(float)progressBar.getMax();
31. int result = (int)(num*100);
32. resultView.setText(result+ "%");
33. if(progressBar.getProgress()==progressBar.getMax()){
34. Toast.makeText(MainActivity.this, R.string.success, 1).show();
35. }
36. break;
37. case -1:
38. Toast.makeText(MainActivity.this, R.string.error, 1).show();
39. break;
40. }
41. }
42. };
43. /** Called when the activity is first created. */
44. @Override
45. public void onCreate(Bundle savedInstanceState) {
46. super.onCreate(savedInstanceState);
47. setContentView(R.layout.main);
48. downloadpathText = (EditText) this.findViewById(R.id.path);
49. progressBar = (ProgressBar) this.findViewById(R.id.downloadbar);
50. resultView = (TextView) this.findViewById(R.id.resultView);
51. Button button = (Button) this.findViewById(R.id.button);
52. button.setOnClickListener(new View.OnClickListener() {
53. @Override
54. public void onClick(View v) {
55. // TODO Auto-generated method stub
56. String path = downloadpathText.getText().toString();
57. System.out.println(Environment.getExternalStorageState()+"------"+Environment.MEDIA_MOUNTED);
58. if(Environment.getExternalStorageState().equals(Environment.MEDIA_MOUNTED)){
59. download(path, Environment.getExternalStorageDirectory());
60. }else{
61. Toast.makeText(MainActivity.this, R.string.sdcarderror, 1).show();
62. }
63. }
64. });
65. }
66. /**
67. * 主线程(UI线程)
68. * 对于显示控件的界面更新只是由UI线程负责，如果是在非UI线程更新控件的属性值，更新后的显示界面不会反映到屏幕上
69. * @param path
70. * @param savedir
71. */
72. private void download(final String path, final File savedir) {
73. new Thread(new Runnable() {
74. @Override
75. public void run() {
76. FileDownloader loader = new FileDownloader(MainActivity.this, path, savedir, 3);
77. progressBar.setMax(loader.getFileSize());//设置进度条的最大刻度为文件的长度
78. try {
79. loader.download(new DownloadProgressListener() {
80. @Override
81. public void onDownloadSize(int size) {//实时获知文件已经下载的数据长度
82. Message msg = new Message();
83. msg.what = 1;
84. msg.getData().putInt("size", size);
85. handler.sendMessage(msg);//发送消息
86. }
87. });
88. } catch (Exception e) {
89. handler.obtainMessage(-1).sendToTarget();
90. }
91. }
92. }).start();
93. }
94. }

DBOpenHelper中代码：

1. package com.android.service;
2. import android.content.Context;
3. import android.database.sqlite.SQLiteDatabase;
4. import android.database.sqlite.SQLiteOpenHelper;
5. public class DBOpenHelper extends SQLiteOpenHelper {
6. private static final String DBNAME = "down.db";
7. private static final int VERSION = 1;
8. public DBOpenHelper(Context context) {
9. super(context, DBNAME, null, VERSION);
10. }
11. @Override
12. public void onCreate(SQLiteDatabase db) {
13. db.execSQL("CREATE TABLE IF NOT EXISTS filedownlog (id
    integer primary key autoincrement, downpath varchar(100), threadid
    INTEGER, downlength INTEGER)");
14. }
15. @Override
16. public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
17. db.execSQL("DROP TABLE IF EXISTS filedownlog");
18. onCreate(db);
19. }
20. }

FileService中代码：

1. package com.android.service;
2. import java.util.HashMap;
3. import java.util.Map;
4. import android.content.Context;
5. import android.database.Cursor;
6. import android.database.sqlite.SQLiteDatabase;
7. public class FileService {
8. private DBOpenHelper openHelper;
9. public FileService(Context context) {
10. openHelper = new DBOpenHelper(context);
11. }
12. /**
13. * 获取每条线程已经下载的文件长度
14. * @param path
15. * @return
16. */
17. public Map<Integer, Integer> getData(String path){
18. SQLiteDatabase db = openHelper.getReadableDatabase();
19. Cursor cursor = db.rawQuery("select threadid, downlength from filedownlog where downpath=?", new String[]{path});
20. Map<Integer, Integer> data = new HashMap<Integer, Integer>();
21. while(cursor.moveToNext()){
22. data.put(cursor.getInt(0), cursor.getInt(1));
23. }
24. cursor.close();
25. db.close();
26. return data;
27. }
28. /**
29. * 保存每条线程已经下载的文件长度
30. * @param path
31. * @param map
32. */
33. public void save(String path,  Map<Integer, Integer> map){//int threadid, int position
34. SQLiteDatabase db = openHelper.getWritableDatabase();
35. db.beginTransaction();
36. try{
37. for(Map.Entry<Integer, Integer> entry : map.entrySet()){
38. db.execSQL("insert into filedownlog(downpath, threadid, downlength) values(?,?,?)",
39. new Object[]{path, entry.getKey(), entry.getValue()});
40. }
41. db.setTransactionSuccessful();
42. }finally{
43. db.endTransaction();
44. }
45. db.close();
46. }
47. /**
48. * 实时更新每条线程已经下载的文件长度
49. * @param path
50. * @param map
51. */
52. public void update(String path, Map<Integer, Integer> map){
53. SQLiteDatabase db = openHelper.getWritableDatabase();
54. db.beginTransaction();
55. try{
56. for(Map.Entry<Integer, Integer> entry : map.entrySet()){
57. db.execSQL("update filedownlog set downlength=? where downpath=? and threadid=?",
58. new Object[]{entry.getValue(), path, entry.getKey()});
59. }
60. db.setTransactionSuccessful();
61. }finally{
62. db.endTransaction();
63. }
64. db.close();
65. }
66. /**
67. * 当文件下载完成后，删除对应的下载记录
68. * @param path
69. */
70. public void delete(String path){
71. SQLiteDatabase db = openHelper.getWritableDatabase();
72. db.execSQL("delete from filedownlog where downpath=?", new Object[]{path});
73. db.close();
74. }
75. }

DownloadProgressListener中代码：

1. package com.android.network;
2. public interface DownloadProgressListener {
3. public void onDownloadSize(int size);
4. }

FileDownloader中代码：

1. package com.android.network;
2. import java.io.File;
3. import java.io.RandomAccessFile;
4. import java.net.HttpURLConnection;
5. import java.net.URL;
6. import java.util.LinkedHashMap;
7. import java.util.Map;
8. import java.util.UUID;
9. import java.util.concurrent.ConcurrentHashMap;
10. import java.util.regex.Matcher;
11. import java.util.regex.Pattern;
12. import com.android.service.FileService;
13. import android.content.Context;
14. import android.util.Log;
15. public class FileDownloader {
16. private static final String TAG = "FileDownloader";
17. private Context context;
18. private FileService fileService;
19. /* 已下载文件长度 */
20. private int downloadSize = 0;
21. /* 原始文件长度 */
22. private int fileSize = 0;
23. /* 线程数 */
24. private DownloadThread[] threads;
25. /* 本地保存文件 */
26. private File saveFile;
27. /* 缓存各线程下载的长度*/
28. private Map<Integer, Integer> data = new ConcurrentHashMap<Integer, Integer>();
29. /* 每条线程下载的长度 */
30. private int block;
31. /* 下载路径  */
32. private String downloadUrl;
33. /**
34. * 获取线程数
35. */
36. public int getThreadSize() {
37. return threads.length;
38. }
39. /**
40. * 获取文件大小
41. * @return
42. */
43. public int getFileSize() {
44. return fileSize;
45. }
46. /**
47. * 累计已下载大小
48. * @param size
49. */
50. protected synchronized void append(int size) {
51. downloadSize += size;
52. }
53. /**
54. * 更新指定线程最后下载的位置
55. * @param threadId 线程id
56. * @param pos 最后下载的位置
57. */
58. protected synchronized void update(int threadId, int pos) {
59. this.data.put(threadId, pos);
60. this.fileService.update(this.downloadUrl, this.data);
61. }
62. /**
63. * 构建文件下载器
64. * @param downloadUrl 下载路径
65. * @param fileSaveDir 文件保存目录
66. * @param threadNum 下载线程数
67. */
68. public FileDownloader(Context context, String downloadUrl, File fileSaveDir, int threadNum) {
69. try {
70. this.context = context;
71. this.downloadUrl = downloadUrl;
72. fileService = new FileService(this.context);
73. URL url = new URL(this.downloadUrl);
74. if(!fileSaveDir.exists()) fileSaveDir.mkdirs();
75. this.threads = new DownloadThread[threadNum];
76. HttpURLConnection conn = (HttpURLConnection) url.openConnection();
77. conn.setConnectTimeout(5*1000);
78. conn.setRequestMethod("GET");
79. conn.setRequestProperty("Accept", "image/gif,
    image/jpeg, image/pjpeg, image/pjpeg, application/x-shockwave-flash,
    application/xaml+xml, application/vnd.ms-xpsdocument,
    application/x-ms-xbap, application/x-ms-application,
    application/vnd.ms-excel, application/vnd.ms-powerpoint,
    application/msword, */*");
80. conn.setRequestProperty("Accept-Language", "zh-CN");
81. conn.setRequestProperty("Referer", downloadUrl);
82. conn.setRequestProperty("Charset", "UTF-8");
83. conn.setRequestProperty("User-Agent", "Mozilla/4.0
    (compatible; MSIE 8.0; Windows NT 5.2; Trident/4.0; .NET CLR 1.1.4322;
    .NET CLR 2.0.50727; .NET CLR 3.0.04506.30; .NET CLR 3.0.4506.2152; .NET
    CLR 3.5.30729)");
84. conn.setRequestProperty("Connection", "Keep-Alive");
85. conn.connect();
86. printResponseHeader(conn);
87. if (conn.getResponseCode()==200) {
88. this.fileSize = conn.getContentLength();//根据响应获取文件大小
89. if (this.fileSize <= 0) throw new RuntimeException("Unkown file size ");
90. String filename = getFileName(conn);//获取文件名称
91. this.saveFile = new File(fileSaveDir, filename);//构建保存文件
92. Map<Integer, Integer> logdata = fileService.getData(downloadUrl);//获取下载记录
93. if(logdata.size()>0){//如果存在下载记录
94. for(Map.Entry<Integer, Integer> entry : logdata.entrySet())
95. data.put(entry.getKey(), entry.getValue());//把各条线程已经下载的数据长度放入data中
96. }
97. if(this.data.size()==this.threads.length){//下面计算所有线程已经下载的数据长度
98. for (int i = 0; i < this.threads.length; i++) {
99. this.downloadSize += this.data.get(i+1);
100. }
101. print("已经下载的长度"+ this.downloadSize);
102. }
103. //计算每条线程下载的数据长度
104. this.block = (this.fileSize %
     this.threads.length)==0? this.fileSize / this.threads.length :
     this.fileSize / this.threads.length + 1;
105. }else{
106. throw new RuntimeException("server no response ");
107. }
108. } catch (Exception e) {
109. print(e.toString());
110. throw new RuntimeException("don't connection this url");
111. }
112. }
113. /**
114. * 获取文件名
115. * @param conn
116. * @return
117. */
118. private String getFileName(HttpURLConnection conn) {
119. String filename = this.downloadUrl.substring(this.downloadUrl.lastIndexOf('/') + 1);
120. if(filename==null || "".equals(filename.trim())){//如果获取不到文件名称
121. for (int i = 0;; i++) {
122. String mine = conn.getHeaderField(i);
123. if (mine == null) break;
124. if("content-disposition".equals(conn.getHeaderFieldKey(i).toLowerCase())){
125. Matcher m = Pattern.compile(".*filename=(.*)").matcher(mine.toLowerCase());
126. if(m.find()) return m.group(1);
127. }
128. }
129. filename = UUID.randomUUID()+ ".tmp";//默认取一个文件名
130. }
131. return filename;
132. }
133. /**
134. *  开始下载文件
135. * @param listener 监听下载数量的变化,如果不需要了解实时下载的数量,可以设置为null
136. * @return 已下载文件大小
137. * @throws Exception
138. */
139. public int download(DownloadProgressListener listener) throws Exception{
140. try {
141. RandomAccessFile randOut = new RandomAccessFile(this.saveFile, "rw");
142. if(this.fileSize>0) randOut.setLength(this.fileSize);
143. randOut.close();
144. URL url = new URL(this.downloadUrl);
145. if(this.data.size() != this.threads.length){
146. this.data.clear();
147. for (int i = 0; i < this.threads.length; i++) {
148. this.data.put(i+1, 0);//初始化每条线程已经下载的数据长度为0
149. }
150. }
151. for (int i = 0; i < this.threads.length; i++) {//开启线程进行下载
152. int downLength = this.data.get(i+1);
153. if(downLength < this.block && this.downloadSize<this.fileSize){//判断线程是否已经完成下载,否则继续下载
154. this.threads[i] = new DownloadThread(this, url, this.saveFile, this.block, this.data.get(i+1), i+1);
155. this.threads[i].setPriority(7);
156. this.threads[i].start();
157. }else{
158. this.threads[i] = null;
159. }
160. }
161. this.fileService.save(this.downloadUrl, this.data);
162. boolean notFinish = true;//下载未完成
163. while (notFinish) {// 循环判断所有线程是否完成下载
164. Thread.sleep(900);
165. notFinish = false;//假定全部线程下载完成
166. for (int i = 0; i < this.threads.length; i++){
167. if (this.threads[i] != null && !this.threads[i].isFinish()) {//如果发现线程未完成下载
168. notFinish = true;//设置标志为下载没有完成
169. if(this.threads[i].getDownLength() == -1){//如果下载失败,再重新下载
170. this.threads[i] = new DownloadThread(this, url, this.saveFile, this.block, this.data.get(i+1), i+1);
171. this.threads[i].setPriority(7);
172. this.threads[i].start();
173. }
174. }
175. }
176. if(listener!=null) listener.onDownloadSize(this.downloadSize);//通知目前已经下载完成的数据长度
177. }
178. fileService.delete(this.downloadUrl);
179. } catch (Exception e) {
180. print(e.toString());
181. throw new Exception("file download fail");
182. }
183. return this.downloadSize;
184. }
185. /**
186. * 获取Http响应头字段
187. * @param http
188. * @return
189. */
190. public static Map<String, String> getHttpResponseHeader(HttpURLConnection http) {
191. Map<String, String> header = new LinkedHashMap<String, String>();
192. for (int i = 0;; i++) {
193. String mine = http.getHeaderField(i);
194. if (mine == null) break;
195. header.put(http.getHeaderFieldKey(i), mine);
196. }
197. return header;
198. }
199. /**
200. * 打印Http头字段
201. * @param http
202. */
203. public static void printResponseHeader(HttpURLConnection http){
204. Map<String, String> header = getHttpResponseHeader(http);
205. for(Map.Entry<String, String> entry : header.entrySet()){
206. String key = entry.getKey()!=null ? entry.getKey()+ ":" : "";
207. print(key+ entry.getValue());
208. }
209. }
210. private static void print(String msg){
211. Log.i(TAG, msg);
212. }
213. }

DownloadThread 中代码：

1. package com.android.network;
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 android.util.Log;
8. public class DownloadThread extends Thread {
9. private static final String TAG = "DownloadThread";
10. private File saveFile;
11. private URL downUrl;
12. private int block;
13. /* 下载开始位置  */
14. private int threadId = -1;
15. private int downLength;
16. private boolean finish = false;
17. private FileDownloader downloader;
18. public DownloadThread(FileDownloader downloader, URL downUrl, File saveFile, int block, int downLength, int threadId) {
19. this.downUrl = downUrl;
20. this.saveFile = saveFile;
21. this.block = block;
22. this.downloader = downloader;
23. this.threadId = threadId;
24. this.downLength = downLength;
25. }
26. @Override
27. public void run() {
28. if(downLength < block){//未下载完成
29. try {
30. HttpURLConnection http = (HttpURLConnection) downUrl.openConnection();
31. http.setConnectTimeout(5 * 1000);
32. http.setRequestMethod("GET");
33. http.setRequestProperty("Accept", "image/gif,
    image/jpeg, image/pjpeg, image/pjpeg, application/x-shockwave-flash,
    application/xaml+xml, application/vnd.ms-xpsdocument,
    application/x-ms-xbap, application/x-ms-application,
    application/vnd.ms-excel, application/vnd.ms-powerpoint,
    application/msword, */*");
34. http.setRequestProperty("Accept-Language", "zh-CN");
35. http.setRequestProperty("Referer", downUrl.toString());
36. http.setRequestProperty("Charset", "UTF-8");
37. int startPos = block * (threadId - 1) + downLength;//开始位置
38. int endPos = block * threadId -1;//结束位置
39. http.setRequestProperty("Range", "bytes=" + startPos + "-"+ endPos);//设置获取实体数据的范围
40. http.setRequestProperty("User-Agent",
    "Mozilla/4.0 (compatible; MSIE 8.0; Windows NT 5.2; Trident/4.0; .NET
    CLR 1.1.4322; .NET CLR 2.0.50727; .NET CLR 3.0.04506.30; .NET CLR
    3.0.4506.2152; .NET CLR 3.5.30729)");
41. http.setRequestProperty("Connection", "Keep-Alive");
42. InputStream inStream = http.getInputStream();
43. byte[] buffer = new byte[1024];
44. int offset = 0;
45. print("Thread " + this.threadId + " start download from position "+ startPos);
46. RandomAccessFile threadfile = new RandomAccessFile(this.saveFile, "rwd");
47. threadfile.seek(startPos);
48. while ((offset = inStream.read(buffer, 0, 1024)) != -1) {
49. threadfile.write(buffer, 0, offset);
50. downLength += offset;
51. downloader.update(this.threadId, downLength);
52. downloader.append(offset);
53. }
54. threadfile.close();
55. inStream.close();
56. print("Thread " + this.threadId + " download finish");
57. this.finish = true;
58. } catch (Exception e) {
59. this.downLength = -1;
60. print("Thread "+ this.threadId+ ":"+ e);
61. }
62. }
63. }
64. private static void print(String msg){
65. Log.i(TAG, msg);
66. }
67. /**
68. * 下载是否完成
69. * @return
70. */
71. public boolean isFinish() {
72. return finish;
73. }
74. /**
75. * 已经下载的内容大小
76. * @return 如果返回值为-1,代表下载失败
77. */
78. public long getDownLength() {
79. return downLength;
80. }
81. }

运行效果如下：       

          完毕。^_^