java多线程下载的实现示例

爱被打了一巴掌 2022-05-29 02:48 450阅读 0赞

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1.  import java.io.File;  
2.  import java.io.FileNotFoundException;  
3.  import java.io.InputStream;  
4.  import java.io.RandomAccessFile;  
5.  import java.net.HttpURLConnection;  
6.  import java.net.URL;  
7.    
8.    
9.  public class Main \{  
10.   
11.     /\*\* 
12.      \* @param args 
13.      \* @throws Exception  
14.      \*/  
15.     public static void main(String\[\] args) throws Exception \{  
16.         new Main().download("http://gdown.baidu.com/data/wisegame/a3d96bf8e8a5102c/baiduliulanqi\_25.apk", 5);  
17.     \}  
18.       
19.     public void download(String downPath, int threadNum) throws Exception\{  
20.         URL url = new URL(downPath);  
21.         HttpURLConnection conn = (HttpURLConnection) url.openConnection();  
22.         conn.setConnectTimeout(5000);  
23.         conn.setRequestMethod("GET");  
24.         //InputStream in = conn.getInputStream();  
25.           
26.         if(conn.getResponseCode() == 200)\{  
27.             int size = conn.getContentLength();  
28.             File file = new File(downPath.substring(downPath.lastIndexOf("/")+1));  
29.               
30.             //"rwd" 会立刻把数据同步到设备上,防止手机没电数据丢失  
31.             RandomAccessFile raf = new RandomAccessFile(file, "rwd");  
32.             raf.setLength(size); //暂时还没数据  
33.             raf.close();  
34.               
35.             int block = size%threadNum == 0 ? size/threadNum : size/threadNum + 1;  
36.             for(int i=0; i<threadNum; i++)\{  
37.                 new DownThread(i, block, url, file).start();  
38.             \}  
39.               
40.         \}else\{  
41.             System.out.println("下载失败");  
42.         \}  
43.           
44.     \}  
45.       
46.     //下载线程类  
47.     private class DownThread extends Thread\{  
48.         private int id;  
49.         private int block; //每个线程下载块大小  
50.         private URL url; //地址  
51.         private File file; //下载保存在哪个文件  
52.           
53.         public DownThread(int i, int block, URL url, File file) \{  
54.             this.id = i;  
55.             this.block = block;  
56.             this.url = url;  
57.             this.file = file;  
58.         \}  
59.           
60.         public void run()\{  
61.             int start = id \* block;  
62.             int end = (id+1) \* block - 1;  
63.               
64.             try \{  
65.                 RandomAccessFile raf = new RandomAccessFile(file, "rwd");  
66.                 raf.seek(start);  
67.                 HttpURLConnection conn = (HttpURLConnection) url.openConnection();  
68.                 conn.setConnectTimeout(5000);  
69.                 conn.setRequestMethod("GET");  
70.                   
71.                 //通过头字段，指定获取文件的位置 bytes="1-1000"  
72.                 conn.setRequestProperty("Range", "bytes=" + start + "-" + end);  
73.                   
74.                 //分段请求文件时，返回码是206  
75.                 if(conn.getResponseCode() == 206)\{  
76.                     byte\[\] buffer = new byte\[1024\];  
77.                     InputStream in = conn.getInputStream();  
78.                     int len = 0;  
79.                     while( (len=in.read(buffer)) != -1)\{  
80.                         raf.write(buffer, 0, len);  
81.                     \}  
82.                     raf.close();  
83.                     in.close();  
84.   
85.                     System.out.println("线程:" + id + "下载完成");  
86.                 \}else\{  
87.                     System.out.println("失败");  
88.                 \}  
89.                   
90.             \} catch (Exception e) \{  
91.                 e.printStackTrace();  
92.             \}  
93.             System.out.println("");  
94.         \}  
95.           
96.     \}  
97.   
98. \}

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