使用java下载http形式的图片

文章来源：http://blog.csdn.net/keepfriend/article/details/53556426

用于下载http形式的图片

以下是自定义的DownUtil类：

[java] view plain copy

1. import java.io.*;  
2. import java.net.*;  
3.   
4. public class DownUtil {  
5.   
6.     private String path;  
7.     private String targetFile;  
8.     private int threadNum;  
9.     private DownThread[] threads;  
10.     private int fileSize;  
11.     private class DownThread extends Thread{  
12.         private int startPos;  
13.         private int currentPartSize;  
14.         private RandomAccessFile currentPart;  
15.         public int length;  
16.         public DownThread(int startPos, int currentPartSize, RandomAccessFile currentPart){  
17.             this.startPos = startPos;  
18.             this.currentPartSize = currentPartSize;  
19.             this.currentPart = currentPart;  
20.         }  
21.         public void run(){  
22.             try{  
23.                 URL url = new URL(path);  
24.                 HttpURLConnection conn = (HttpURLConnection) url.openConnection();  
25.                 conn.setConnectTimeout(5 * 1000);  
26.                 conn.setRequestMethod("GET");  
27.                 conn.setRequestProperty(  
28.                     "Accept", "image/gif, image/jpeg, image/pjpeg, image/pjpeg, "  
29.                     + "application/x-shockwave-flash, application/xaml+xml, "  
30.                     + "application/vnd.ms-xpsdocument, application/x-ms-xbap, "  
31.                     + "application/x-ms-application, application/vnd.ms-excel, "  
32.                     + "application/vnd.ms-powerpoint, application/msword, */*");  
33.                 conn.setRequestProperty("Accept-Language", "zh-CN");  
34.                 conn.setRequestProperty("Charset", "UTF-8");  
35.                 InputStream inStream = conn.getInputStream();  
36.                 inStream.skip(this.startPos);  
37.                 byte[] buffer = new byte[1024];  
38.                 int hasRead = 0;  
39.                 // Read network data and write to a local file  
40.                 while(length < currentPartSize && (hasRead = inStream.read(buffer)) !=  -1){  
41.                     currentPart.write(buffer, 0, hasRead);  
42.                     length += hasRead;  
43.                 }  
44.                 currentPart.close();  
45.                 inStream.close();  
46.             }catch(Exception e){  
47.                 e.printStackTrace();  
48.             }  
49.         }  
50.     }  
51.   
52.     public DownUtil(String path, String targetFile, int threadNum) {  
53.         this.path = path;  
54.         this.threadNum = threadNum;  
55.         this.threads = new DownThread[threadNum];  
56.         this.targetFile = targetFile;  
57.     }  
58.   
59.     public void download() throws Exception{  
60.         URL url = new URL(path);  
61.         HttpURLConnection conn = (HttpURLConnection) url.openConnection();  
62.         conn.setConnectTimeout(5 * 1000);  
63.         conn.setRequestMethod("GET");  
64.         conn.setRequestProperty(  
65.                 "Accept", "image/gif, image/jpeg, image/pjpeg, image/pjpeg, "  
66.                 + "application/x-shockwave-flash, application/xaml+xml, "  
67.                 + "application/vnd.ms-xpsdocument, application/x-ms-xbap, "  
68.                 + "application/x-ms-application, application/vnd.ms-excel, "  
69.                 + "application/vnd.ms-powerpoint, application/msword, */*");  
70.         conn.setRequestProperty("Accept-Language", "zh-CN");  
71.         conn.setRequestProperty("Charset", "UTF-8");  
72.         conn.setRequestProperty("Connection", "Keep-Alive");  
73.   
74.         fileSize = conn.getContentLength();  
75.         conn.disconnect();  
76.         int currentPartSize = fileSize / threadNum + 1;  
77.         RandomAccessFile file = new RandomAccessFile(targetFile, "rw");  
78.         file.setLength(fileSize);  
79.         file.close();  
80.         // Multi-threaded download  
81.         for(int i = 0; i < threadNum; ++i){  
82.             int startPos = i * currentPartSize;  
83.             RandomAccessFile currentPart = new RandomAccessFile(targetFile, "rw");  
84.             currentPart.seek(startPos);  
85.             threads[i] = new DownThread(startPos, currentPartSize, currentPart);  
86.             threads[i].start();  
87.         }  
88.     }  
89.     // Gets the percentage of completion of the download  
90.     public double getCompleteRate(){  
91.         int sumSize = 0;  
92.         for(int i = 0; i < threadNum; ++i){  
93.             sumSize += threads[i].length;  
94.         }  
95.         return sumSize * 1.0 / fileSize;  
96.     }  
97. }  

这是主程序：

[java] view plain copy

1. public class MultiThreadedDownload {  
2.   
3.     public static void main(String[] args) throws Exception{  
4.         DownUtil downUtil = new DownUtil("http://imgsrc.baidu.com/baike/pic" +  
5.                 "/item/8644ebf81a4c510f64b65cfa6559252dd52aa5e4.jpg", "liuyan.jpg", 4);  
6.         downUtil.download();  
7.         new Thread(()->{  
8.             while(downUtil.getCompleteRate() < 1){  
9.                 System.out.println("已完成：" + downUtil.getCompleteRate());  
10.                 try{  
11.                     Thread.sleep(1000);  
12.                 }catch(Exception e){  
13.                     e.printStackTrace();  
14.                 }  
15.             }  
16.         }).start();  
17.     }  
18. }  

谢谢浏览！