Android中級篇之多線程下載

下面看代碼部分：

1.布局文件 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. >
7. <TextView
8. android:layout_width="fill_parent"
9. android:layout_height="wrap_content"
10. android:text="下載路徑"
11. />
12. <EditText
13. android:id="@+id/mEditText"
14. android:layout_width="fill_parent"
15. android:layout_height="wrap_content"
16. android:singleLine="true"
17. android:text="http://android.yesky.com/uploads/attachments/2010-04/27/a5964152.jpg"/>
18. <ProgressBar
19. android:id="@+id/mBar"
20. android:layout_width="fill_parent"
21. android:layout_height="wrap_content"
22. android:visibility="invisible"
23. style="?android:attr/progressBarStyleHorizontal"/>
24. <Button
25. android:id="@+id/mButton"
26. android:layout_width="fill_parent"
27. android:layout_height="wrap_content"
28. android:text="下載"/>
29. </LinearLayout>

2.下載工具類 Download.java

1. package com.yin.downloader.utils;
2. import java.io.File;
3. import java.io.IOException;
4. import java.io.InputStream;
5. import java.io.RandomAccessFile;
6. import java.net.HttpURLConnection;
7. import java.net.MalformedURLException;
8. import java.net.URL;
9. import android.content.Context;
10. import android.util.Log;
11. public class Download {
12. private String SDPath = null;
13. private static final String TAG = "com.yin.download";
14. private RandomAccessFile randomFile = null;
15. private URL url;
16. private Context context;
17. private String urlStr;
18. private String fileName;
19. private int fileSize;
20. private int totalReadSize;
21. public Download(String urlStr,String fileName,String SDPath,Context context){
22. this.context = context;
23. this.fileName = fileName;
24. this.urlStr = urlStr;
25. this.SDPath = SDPath;
26. }
28. public void downloadFile(){
29. try {
30. File file = new File(SDPath+fileName);
31. url = new URL(urlStr);
32. HttpURLConnection conn = (HttpURLConnection) url.openConnection();
33. conn.setRequestMethod("GET");
34. //獲得下載文件的大小
35. fileSize = conn.getContentLength();
36. //設置線程的大小，考慮手機的性能，並不是越大越好
37. int threadSize = 3;
38. //每個線程下載文件+的部分大小 +1 避免文件下載不完全
39. int block = fileSize / threadSize +1;
40. for(int i=0;i<3;i++){
41. int startPosition = i * block;
42. //創建可任意位置讀取的文件
43. randomFile = new RandomAccessFile(file, "rw");
44. randomFile.seek(startPosition);
45. new DownloadThread(i+1, startPosition, block, randomFile).start();
46. }
48. } catch (MalformedURLException e) {
49. Log.e(TAG, "MalformedURLException");
50. e.printStackTrace();
51. } catch (IOException e) {
52. Log.e(TAG, "IOException");
53. e.printStackTrace();
54. }
55. }
57. //下載文件的線程
58. private class DownloadThread extends Thread{
60. private int threadID;
61. private int startPosition;
62. private int block;
63. private RandomAccessFile randomFile;
64. public DownloadThread(int threadID, int startPosition, int block,
65. RandomAccessFile randomFile) {
66. super();
67. this.threadID = threadID;
68. this.startPosition = startPosition;
69. this.block = block;
70. this.randomFile = randomFile;
71. }
73. public void run() {
74. try {
75. HttpURLConnection conn = (HttpURLConnection) url.openConnection();
76. conn.setRequestMethod("GET");
77. //文件下載位置 規定的格式 “byte=xxxx-”
78. String start = "bytes="+startPosition + "-";
79. //設置文件開始的下載位置
80. conn.setRequestProperty("Range", start);
81. InputStream is = conn.getInputStream();
82. byte[] buffer = new byte[4*1024];
83. int len = -1;
84. int readFileSize = 0;
85. while((readFileSize < block) && ((len = is.read(buffer)) != -1)){
86. randomFile.write(buffer,0,len);
87. readFileSize += len ;
88. totalReadSize += readFileSize;
89. }
90. System.out.println("線程 ："+threadID+" 下載完成");
91. is.close();
92. randomFile.close();
93. conn.disconnect();
95. } catch (IOException e) {
96. Log.e(TAG+":child", "IOException");
97. e.printStackTrace();
98. }
99. }
100. }
101. public int getFileSize() {
102. return fileSize;
103. }
104. public void setFileSize(int fileSize) {
105. this.fileSize = fileSize;
106. }
107. public int getTotalReadSize() {
108. return totalReadSize;
109. }
110. public void setTotalReadSize(int totalReadSize) {
111. this.totalReadSize = totalReadSize;
112. }
113. }