Java多线程下载源码

Java多线程下载源码

1. import java.io.File;  
2. import java.io.FileNotFoundException;  
3. import java.io.IOException;  
4. import java.io.InputStream;  
5. import java.io.RandomAccessFile;  
6. import java.net.HttpURLConnection;  
7. import java.net.URL;  
8.   
9. public class MyThreadDownloader  
10. {  
11.     public static void main(String args[])  
12.     {  
13.         // 下载连接   
14.         String downloadURL = "http://localhost:8080/cangjingkong.avi";  
15.         // 下载开启线程数   
16.         int threadSize = 3;  
17.         try  
18.         {  
19.             new MyThreadDownloader().download(downloadURL, threadSize);  
20.         }  
21.         catch (Exception e)  
22.         {  
23.             e.printStackTrace();  
24.         }  
25.     }  
26.   
27.     private void download(String downloadURL, int threadSize) throws Exception  
28.     {  
29.         String fileName = getFileName(downloadURL);  
30.   
31.         URL url = new URL(downloadURL);  
32.   
33.         HttpURLConnection connection = (HttpURLConnection) url.openConnection();  
34.         // 设置超时   
35.         connection.setConnectTimeout(5000);  
36.         // 设置请求方式   
37.         connection.setRequestMethod("GET");  
38.         // 获取文件长度   
39.         int fileLength = connection.getContentLength();  
40.         // 保存文件   
41.         File localFile = new File(fileName);  
42.         // 临时文件不存内存,直接进行数据读写"rwd"   
43.         RandomAccessFile randomAccessFile = new RandomAccessFile(localFile,"rwd");  
44.         // 直接创建与服务器获取长度相等的文件   
45.         randomAccessFile.setLength(fileLength);  
46.         // 文件操作over,关闭   
47.         randomAccessFile.close();  
48.   
49.         // 计算每条线程负责下载的数据量   
50.         int downblock = fileLength % threadSize == 0 ? fileLength / threadSize  
51.                 : fileLength / threadSize + 1;  
52.         // 分配每条线程下载任务   
53.         for (int threadID = 0; threadID < threadSize; threadID++)  
54.         {  
55.             //开启多线程下载任务   
56.             new DownloadThread(threadID, url, localFile, downblock).start();  
57.         }  
58.     }  
59.   
60.   
61.     /** 
62.      * @param downloadURL 
63.      *            下载连接 
64.      * @return 返回下载文件名 
65.      */  
66.     private String getFileName(String downloadURL)  
67.     {  
68.         return downloadURL.substring(downloadURL.lastIndexOf("/") + 1);  
69.     }  
70.   
71.     public final class DownloadThread extends Thread  
72.     {  
73.         private int threadID;      // 当前下载线程ID   
74.         private URL url;           // 下载连接   
75.         private File localFile;    // 目标文件   
76.         private int downblock;     // 分段下载长度   
77.         private int startPosition; // 开始下载位置   
78.         private int endPosition;   // 结束下载位置   
79.   
80.         public DownloadThread(int threadID, URL url, File localFile,  
81.                 int downblock)  
82.         {  
83.             this.threadID = threadID;  
84.             this.url = url;  
85.             this.localFile = localFile;  
86.             this.downblock = downblock;  
87.         }  
88.   
89.         public void run()  
90.         {  
91.             startPosition = threadID * downblock;  
92.             endPosition = (threadID + 1) * downblock;  
93.             try  
94.             {  
95.                 RandomAccessFile randomAccessFile = new RandomAccessFile(localFile,"rwd");  
96.                 randomAccessFile.seek(startPosition);  
97.                   
98.                 HttpURLConnection connection = (HttpURLConnection) url.openConnection();  
99.                 connection.setReadTimeout(5000);  
100.                 connection.setRequestMethod("GET");  
101.                 connection.setRequestProperty("Range", "bytes="+startPosition+"-"+endPosition);  
102.                   
103.                 InputStream inputStream = connection.getInputStream();  
104.                 byte[] buffer = new byte[1024];  
105.                 int len = 0;  
106.                 while ((len = inputStream.read(buffer)) != -1)  
107.                 {  
108.                     randomAccessFile.write(buffer, 0, len);  
109.                 }  
110.                   
111.                 inputStream.close();  
112.                 randomAccessFile.close();  
113.                   
114.                 System.out.println("第"+(threadID+1)+"条线程已经下载完成");  
115.                   
116.             }  
117.             catch (FileNotFoundException e)  
118.             {  
119.                 e.printStackTrace();  
120.             }  
121.             catch (IOException e)  
122.             {  
123.                 e.printStackTrace();  
124.             }  
125.         }  
126.     }  
127. }