Java多線程下載輔助類實現

使用聲明：

類名：MultiThreadDownloadUtil

API：

(1)download(String path,int count);

path：文件URL；

count：線程數量；

1. package org.xiazdong.multidownload.util;
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;
10. public class MultiThreadDownloadUtil{
11. private static int filesize;
12. private static int block;
13. private static String filename;
14. private static int downloadsize;
15. private class MyThread extends Thread{
16. private int i; //線程ID
17. private String path; //下載文件的URL
19. public MyThread(int i, String path) {
20. this.i = i;
21. this.path = path;
22. downloadsize = 0;
23. }
24. @Override
25. public void run() {
26. try{
27. System.out.println("線程"+(i+1)+"開始下載");
28. //1.打開文件，並定位位置
29. RandomAccessFile raf = new RandomAccessFile(new File(filename), "rwd");
30. raf.seek(i*block); //定位到此線程要負責下載的位置
31. int start = i*block;
32. int end = (i+1)*block-1;
33. //2.連接服務器
34. URL url = new URL(path);
35. HttpURLConnection conn = (HttpURLConnection)url.openConnection();
36. conn.setRequestMethod("GET");
37. conn.setRequestProperty("range", "bytes="+start+"-"+end); //發出請求頭
39. if(conn.getResponseCode()==206){ //注意：分段下載的返回碼為206，而不是200
40. InputStream in = conn.getInputStream();
41. int length = 0;
42. byte[]data = new byte[1024];
43. while((length=in.read(data))!=-1){
44. raf.write(data,0,length); //寫入本地文件
45. }
46. }
47. //顯示下載進度
48. downloadsize += (end-start);
49. System.out.println("已下載"+downloadsize/1024.0+"k,共"+filesize/1024.0+"k");
50. //3.關閉文件
51. raf.close();
52. System.out.println("線程"+(i+1)+"結束下載...");
53. }
54. catch(Exception e){
55. e.printStackTrace();
56. }
57. }
58. }
59. /**
60. * 下載文件
61. * @param path URL
62. * @param threadcount 線程數
63. * @throws Exception
64. */
65. public static void download(String path,int threadcount) throws Exception{
66. filename = path.substring(path.lastIndexOf('/')+1);
67. filesize = getFileSize(path);
68. block = getBlockSize(filesize,threadcount);
69. createLocalRandomFile(filesize);
70. MultiThreadDownloadUtil mdu = new MultiThreadDownloadUtil();
71. for(int i=0;i<threadcount;i++){
72. mdu.new MyThread(i,path).start();
73. }
74. }
75. /**
76. * 創建一個本地文件，並設置文件的大小
77. * @param filesize
78. * @throws Exception
79. */
80. private static void createLocalRandomFile(int filesize) throws Exception {
81. RandomAccessFile raf = new RandomAccessFile(new File(filename), "rwd");
82. raf.setLength(filesize);
83. raf.close();
84. }
85. /**
86. * 根據文件總大小和線程數求出每個線程要下載的數據量
87. * @param filesize
88. * @param threadcount
89. * @return
90. */
91. private static int getBlockSize(int filesize, int threadcount) {
92. return filesize%threadcount==0?filesize/threadcount:(filesize/threadcount+1);
93. }
94. /**
95. * 求出文件總大小
96. * @param path
97. * @return
98. * @throws Exception
99. */
100. private static int getFileSize(String path) throws Exception{
101. URL url = new URL(path);
102. HttpURLConnection conn = (HttpURLConnection)url.openConnection();
103. conn.setRequestMethod("GET");
104. if(conn.getResponseCode()==200){
105. return conn.getContentLength();
106. }
107. else{
108. return 0;
109. }
110. }
111. }

測試類：

1. package org.xiazdong.download;
3. import org.xiazdong.multidownload.util.MultiThreadDownloadUtil;
6. public class MultiThreadDownloader {
8. public static void main(String[] args) throws Exception {
9. int threadCount = 3; //指定線程數量
10. String path = "http://dlc2.pconline.com.cn/filedown_61761_6694063/drivethelife2010_pconline_setup.exe"; //指定下載文件路徑
11. MultiThreadDownloadUtil.download(path, threadCount);
12. }
13. }

將此文件下載到工程目錄後，運行可用；