Android中多线程下载文件

一时失言乱红尘 2022-06-14 23:07 261阅读 0赞

**实现原理**

(1)首先获得下载文件的长度，然后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：

![SouthEast][]（网上找的图）

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=?

之前练习时的一个demo，不多说了，直接上代码吧，有关断点续传，需要使用[数据库][Link 1]，不再加了，网上有很多成熟的项目可以直接用。

**实例**

MainApp：

**\[java\]** [ view plain][view plain] [ copy][view plain]

1.  package com.amos.app; 
2.  
3.  import java.io.File; 
4.  import java.io.IOException; 
5.  import java.net.MalformedURLException; 
6.  import java.net.URL; 
7.  import java.net.URLConnection; 
8.  import com.amos.download.R; 
9.  import android.annotation.SuppressLint; 
10. import android.app.Activity; 
11. import android.os.Bundle; 
12. import android.os.Environment; 
13. import android.os.Handler; 
14. import android.os.Message; 
15. import android.util.Log; 
16. import android.view.View; 
17. import android.view.View.OnClickListener; 
18. import android.widget.ProgressBar; 
19. import android.widget.TextView; 
20. import android.widget.Toast; 
21. 
22. /\*\*
23.  \* @author yangxiaolong
24.  \* @2014-5-6
25.  \*/
26. public class MainApp extends Activity implements OnClickListener \{ 
27. 
28. private static final String TAG = MainApp.class.getSimpleName(); 
29. 
30. /\*\* 显示下载进度TextView \*/
31. private TextView mMessageView; 
32. /\*\* 显示下载进度ProgressBar \*/
33. private ProgressBar mProgressbar; 
34. 
35. @Override
36. protected void onCreate(Bundle savedInstanceState) \{ 
37. super.onCreate(savedInstanceState); 
38.  setContentView(R.layout.progress\_activity); 
39.  findViewById(R.id.download\_btn).setOnClickListener(this); 
40.  mMessageView = (TextView) findViewById(R.id.download\_message); 
41.  mProgressbar = (ProgressBar) findViewById(R.id.download\_progress); 
42.  \} 
43. 
44. @Override
45. public void onClick(View v) \{ 
46. if (v.getId() == R.id.download\_btn) \{ 
47.  doDownload(); 
48.  \} 
49.  \} 
50. 
51. /\*\*
52.  \* 使用Handler更新UI界面信息
53.  \*/
54. @SuppressLint("HandlerLeak") 
55.  Handler mHandler = new Handler() \{ 
56. @Override
57. public void handleMessage(Message msg) \{ 
58. 
59.  mProgressbar.setProgress(msg.getData().getInt("size")); 
60. 
61. float temp = (float) mProgressbar.getProgress() 
62.  / (float) mProgressbar.getMax(); 
63. 
64. int progress = (int) (temp \* 100); 
65. if (progress == 100) \{ 
66.  Toast.makeText(MainApp.this, "下载完成！", Toast.LENGTH\_LONG).show(); 
67.  \} 
68.  mMessageView.setText("下载进度:" \+ progress + " %"); 
69. 
70.  \} 
71.  \}; 
72. 
73. /\*\*
74.  \* 下载准备工作，获取SD卡路径、开启线程
75.  \*/
76. private void doDownload() \{ 
77. // 获取SD卡路径
78.  String path = Environment.getExternalStorageDirectory() 
79.  \+ "/amosdownload/"; 
80.  File file = new File(path); 
81. // 如果SD卡目录不存在创建
82. if (!file.exists()) \{ 
83.  file.mkdir(); 
84.  \} 
85. // 设置progressBar初始化
86.  mProgressbar.setProgress(0); 
87. 
88. // 简单起见，我先把URL和文件名称写死，其实这些都可以通过HttpHeader获取到
89.  String downloadUrl = "http://gdown.baidu.com/data/wisegame/91319a5a1dfae322/baidu\_16785426.apk"; 
90.  String fileName = "baidu\_16785426.apk"; 
91. int threadNum = 5; 
92.  String filepath = path + fileName; 
93.  Log.d(TAG, "download file path:" \+ filepath); 
94.  downloadTask task = new downloadTask(downloadUrl, threadNum, filepath); 
95.  task.start(); 
96.  \} 
97. 
98. /\*\*
99.  \* 多线程文件下载
100.  \* 
101.  \* @author yangxiaolong
102.  \* @2014-8-7
103.  \*/
104. class downloadTask extends Thread \{ 
105. private String downloadUrl;// 下载链接地址
106. private int threadNum;// 开启的线程数
107. private String filePath;// 保存文件路径地址
108. private int blockSize;// 每一个线程的下载量
109. 
110. public downloadTask(String downloadUrl, int threadNum, String fileptah) \{ 
111. this.downloadUrl = downloadUrl; 
112. this.threadNum = threadNum; 
113. this.filePath = fileptah; 
114.  \} 
115. 
116. @Override
117. public void run() \{ 
118. 
119.  FileDownloadThread\[\] threads = new FileDownloadThread\[threadNum\]; 
120. try \{ 
121.  URL url = new URL(downloadUrl); 
122.  Log.d(TAG, "download file http path:" \+ downloadUrl); 
123.  URLConnection conn = url.openConnection(); 
124. // 读取下载文件总大小
125. int fileSize = conn.getContentLength(); 
126. if (fileSize <= 0) \{ 
127.  System.out.println("读取文件失败"); 
128. return; 
129.  \} 
130. // 设置ProgressBar最大的长度为文件Size
131.  mProgressbar.setMax(fileSize); 
132. 
133. // 计算每条线程下载的数据长度
134.  blockSize = (fileSize % threadNum) == 0 ? fileSize / threadNum 
135.  : fileSize / threadNum + 1; 
136. 
137.  Log.d(TAG, "fileSize:" \+ fileSize + " blockSize:"); 
138. 
139.  File file = new File(filePath); 
140. for (int i = 0; i < threads.length; i++) \{ 
141. // 启动线程，分别下载每个线程需要下载的部分
142.  threads\[i\] = new FileDownloadThread(url, file, blockSize, 
143.  (i + 1)); 
144.  threads\[i\].setName("Thread:" \+ i); 
145.  threads\[i\].start(); 
146.  \} 
147. 
148. boolean isfinished = false; 
149. int downloadedAllSize = 0; 
150. while (!isfinished) \{ 
151.  isfinished = true; 
152. // 当前所有线程下载总量
153.  downloadedAllSize = 0; 
154. for (int i = 0; i < threads.length; i++) \{ 
155.  downloadedAllSize += threads\[i\].getDownloadLength(); 
156. if (!threads\[i\].isCompleted()) \{ 
157.  isfinished = false; 
158.  \} 
159.  \} 
160. // 通知handler去更新视图组件
161.  Message msg = new Message(); 
162.  msg.getData().putInt("size", downloadedAllSize); 
163.  mHandler.sendMessage(msg); 
164. // Log.d(TAG, "current downloadSize:" + downloadedAllSize);
165.  Thread.sleep(1000);// 休息1秒后再读取下载进度
166.  \} 
167.  Log.d(TAG, " all of downloadSize:" \+ downloadedAllSize); 
168. 
169.  \} catch (MalformedURLException e) \{ 
170.  e.printStackTrace(); 
171.  \} catch (IOException e) \{ 
172.  e.printStackTrace(); 
173.  \} catch (InterruptedException e) \{ 
174.  e.printStackTrace(); 
175.  \} 
176. 
177.  \} 
178.  \} 
179. 
180. \}

FileDownloadThread:

**\[java\]** [ view plain][view plain] [ copy][view plain]

1.  package com.amos.app; 
2.  
3.  import java.io.BufferedInputStream; 
4.  import java.io.File; 
5.  import java.io.IOException; 
6.  import java.io.RandomAccessFile; 
7.  import java.net.URL; 
8.  import java.net.URLConnection; 
9.  import android.util.Log; 
10. 
11. /\*\*
12.  \* 文件下载类
13.  \* 
14.  \* @author yangxiaolong
15.  \* @2014-5-6
16.  \*/
17. public class FileDownloadThread extends Thread \{ 
18. 
19. private static final String TAG = FileDownloadThread.class.getSimpleName(); 
20. 
21. /\*\* 当前下载是否完成 \*/
22. private boolean isCompleted = false; 
23. /\*\* 当前下载文件长度 \*/
24. private int downloadLength = 0; 
25. /\*\* 文件保存路径 \*/
26. private File file; 
27. /\*\* 文件下载路径 \*/
28. private URL downloadUrl; 
29. /\*\* 当前下载线程ID \*/
30. private int threadId; 
31. /\*\* 线程下载数据长度 \*/
32. private int blockSize; 
33. 
34. /\*\*
35.  \* 
36.  \* @param url:文件下载地址
37.  \* @param file:文件保存路径
38.  \* @param blocksize:下载数据长度
39.  \* @param threadId:线程ID
40.  \*/
41. public FileDownloadThread(URL downloadUrl, File file, int blocksize, 
42. int threadId) \{ 
43. this.downloadUrl = downloadUrl; 
44. this.file = file; 
45. this.threadId = threadId; 
46. this.blockSize = blocksize; 
47.  \} 
48. 
49. @Override
50. public void run() \{ 
51. 
52.  BufferedInputStream bis = null; 
53.  RandomAccessFile raf = null; 
54. 
55. try \{ 
56.  URLConnection conn = downloadUrl.openConnection(); 
57.  conn.setAllowUserInteraction(true); 
58. 
59. int startPos = blockSize \* (threadId - 1);//开始位置
60. int endPos = blockSize \* threadId - 1;//结束位置
61. //设置当前线程下载的起点、终点
62.  conn.setRequestProperty("Range", "bytes=" \+ startPos + "-" \+ endPos); 
63.  System.out.println(Thread.currentThread().getName() + " bytes="
64.  \+ startPos + "-" \+ endPos); 
65. 
66. byte\[\] buffer = new byte\[1024\]; 
67.  bis = new BufferedInputStream(conn.getInputStream()); 
68. 
69.  raf = new RandomAccessFile(file, "rwd"); 
70.  raf.seek(startPos); 
71. int len; 
72. while ((len = bis.read(buffer, 0, 1024)) != -1) \{ 
73.  raf.write(buffer, 0, len); 
74.  downloadLength += len; 
75.  \} 
76.  isCompleted = true; 
77.  Log.d(TAG, "current thread task has finished,all size:"
78.  \+ downloadLength); 
79. 
80.  \} catch (IOException e) \{ 
81.  e.printStackTrace(); 
82.  \} finally \{ 
83. if (bis != null) \{ 
84. try \{ 
85.  bis.close(); 
86.  \} catch (IOException e) \{ 
87.  e.printStackTrace(); 
88.  \} 
89.  \} 
90. if (raf != null) \{ 
91. try \{ 
92.  raf.close(); 
93.  \} catch (IOException e) \{ 
94.  e.printStackTrace(); 
95.  \} 
96.  \} 
97.  \} 
98.  \} 
99. 
100. /\*\*
101.  \* 线程文件是否下载完毕
102.  \*/
103. public boolean isCompleted() \{ 
104. return isCompleted; 
105.  \} 
106. 
107. /\*\*
108.  \* 线程下载文件长度
109.  \*/
110. public int getDownloadLength() \{ 
111. return downloadLength; 
112.  \} 
113. 
114. \}

[SouthEast]: /images/20220615/ef55b6bdc44c47febccfa65bb8e4e02c.png
[Link 1]: http://lib.csdn.net/base/mysql
[view plain]: http://blog.csdn.net/mad1989/article/details/38421465#