断点续传（客户端和服务器端实现）

今天药忘吃喽~ 2022-07-16 09:53 290阅读 0赞

# [断点续传（客户端和服务器端实现） ][Link 1] #

2013-09-05 15:51  4360人阅读 [评论][Link 2](4) 收藏 [举报][Link 3]

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Java*（5）* ![arrow_triangle_20_down.jpg][] ![arrow_triangle_up.jpg][]

[作者同类文章][Link 4] *X*

所谓断点续传，也就是要从文件已经下载的地方开始继续下载。

客户端从服务器端下载文件，服务器端支持分段下载，这样子，还可以进行多线程分段下载（在此就不提供了）。

服务器端的支持：

**\[java\]** [ view plain][view plain] [ copy][view plain] [ print][view plain] [?][view plain]

1.  public class DownloadServlet extends HttpServlet \{  
2.    
3.      /\*\* 
4.       \*  
5.       \*/  
6.      private static final long serialVersionUID = 1L;  
7.        
8.      protected void doGet(HttpServletRequest req, HttpServletResponse resp)  
9.              throws ServletException, IOException \{  
10.         // TODO Auto-generated method stub  
11.         OutputStream os = null;  
12.         FileInputStream is = null;  
13.         try \{  
14.             File f = new File(  
15.                     "/home/agilemobi/Desktop/laolian\_client\_for\_android\_v1.0.apk");  
16.             is = new FileInputStream(f);  
17.             long fileSize = f.length();  
18.             resp.setHeader("Accept-Ranges", "bytes");  
19. //          resp.setHeader("Content-Length", fileSize + "");  
20.             String range = req.getHeader("Range");  
21.             int status = HttpServletResponse.SC\_OK; // 返回的状态码，默认200，首次下载  
22.             // 如果range下载区域为空，则首次下载，  
23.             if(range == null)\{  
24.                 range = "bytes=0-";  
25.             \} else \{  
26.                 // 通过下载区域下载，使用206状态码支持断点续传  
27.                 status = HttpServletResponse.SC\_PARTIAL\_CONTENT;  
28.             \}  
29.               
30.             long start = 0, end = 0;  
31.             if (null != range && range.startsWith("bytes=")) \{  
32.                 String\[\] values = range.split("=")\[1\].split("-");  
33.                 start = Integer.parseInt(values\[0\]);  
34.                 // 如果服务器端没有设置end结尾，默认取下载全部  
35.                 if(values.length == 1)\{  
36.                     end = fileSize;  
37.                 \} else \{  
38.                     end = Integer.parseInt(values\[1\]);  
39.                 \}  
40.                    
41.             \}  
42.             // 此次数据响应大小  
43.             long responseSize = 0;  
44.             if (end != 0 && end > start) \{  
45.                 responseSize = end - start + 1;  
46.                 // 返回当前连接下载的数据大小,也就是此次数据传输大小  
47.                 resp.addHeader("Content-Length", "" + (responseSize));  
48.             \} else \{  
49.                 responseSize = Integer.MAX\_VALUE;  
50.             \}  
51.               
52.             byte\[\] buffer = new byte\[4096\];  
53.             // 设置响应状态码  
54.             resp.setStatus(status);  
55.             if(status == HttpServletResponse.SC\_PARTIAL\_CONTENT)\{  
56.                 // 设置断点续传的Content-Range传输字节和总字节  
57.                 resp.addHeader("Content-Range", "bytes " + start + "-" + (fileSize - 1) + "/" + fileSize);  
58.             \}  
59.             // 设置响应客户端内容类型  
60.             resp.setContentType("application/x-download");  
61.             // 设置响应客户端头  
62.             resp.addHeader("Content-Disposition", "attachment;filename=laolian\_client\_for\_android\_v1.0.apk");  
63.             // 当前需要下载文件的大小  
64.             int needSize = (int)responseSize;  
65.             if(start != 0)\{  
66.                 // 跳已经传输过的字节  
67.                 is.skip(start);  
68.             \}  
69.             os = resp.getOutputStream();  
70.             while (needSize > 0) \{  
71.                 int len = is.read(buffer);  
72.                 if (needSize < buffer.length) \{  
73.                     os.write(buffer, 0, needSize);  
74.                 \} else \{  
75.                     os.write(buffer, 0, len);  
76.                     // 如果读取文件大小小于缓冲字节大小，表示已写入完，直接跳出  
77.                     if (len < buffer.length) \{  
78.                         break;  
79.                     \}  
80.                 \}  
81.                 // 不断更新当前可下载文件大小  
82.                 needSize -= buffer.length;  
83.             \}  
84.         \} catch (IOException e) \{  
85.             e.printStackTrace();  
86.             return;  
87.         \} finally \{  
88.             if (is != null)  
89.                 is.close();  
90.             if (os != null)  
91.                 os.close();  
92.         \}  
93.     \}  
94.   
95.     @Override  
96.     protected void doPost(HttpServletRequest req, HttpServletResponse resp)  
97.             throws ServletException, IOException \{  
98.         // TODO Auto-generated method stub  
99.         super.doPost(req, resp);  
100.           
101.     \}  
102.   
103. \}

![save_snippets.png][]

public class DownloadServlet extends HttpServlet {
    
    	/**
    	 * 
    	 */
    	private static final long serialVersionUID = 1L;
    	
    	protected void doGet(HttpServletRequest req, HttpServletResponse resp)
    			throws ServletException, IOException {
    		// TODO Auto-generated method stub
    		OutputStream os = null;
    		FileInputStream is = null;
    		try {
    			File f = new File(
    					"/home/agilemobi/Desktop/laolian_client_for_android_v1.0.apk");
    			is = new FileInputStream(f);
    			long fileSize = f.length();
    			resp.setHeader("Accept-Ranges", "bytes");
    //			resp.setHeader("Content-Length", fileSize + "");
    			String range = req.getHeader("Range");
    			int status = HttpServletResponse.SC_OK; // 返回的状态码，默认200，首次下载
                // 如果range下载区域为空，则首次下载，
                if(range == null){
                    range = "bytes=0-";
                } else {
                    // 通过下载区域下载，使用206状态码支持断点续传
                    status = HttpServletResponse.SC_PARTIAL_CONTENT;
                }
                
                long start = 0, end = 0;
                if (null != range && range.startsWith("bytes=")) {
                    String[] values = range.split("=")[1].split("-");
                    start = Integer.parseInt(values[0]);
                    // 如果服务器端没有设置end结尾，默认取下载全部
                    if(values.length == 1){
                        end = fileSize;
                    } else {
                        end = Integer.parseInt(values[1]);
                    }
                     
                }
                // 此次数据响应大小
                long responseSize = 0;
                if (end != 0 && end > start) {
                    responseSize = end - start + 1;
                    // 返回当前连接下载的数据大小,也就是此次数据传输大小
                    resp.addHeader("Content-Length", "" + (responseSize));
                } else {
                    responseSize = Integer.MAX_VALUE;
                }
                
                byte[] buffer = new byte[4096];
                // 设置响应状态码
                resp.setStatus(status);
                if(status == HttpServletResponse.SC_PARTIAL_CONTENT){
                    // 设置断点续传的Content-Range传输字节和总字节
                    resp.addHeader("Content-Range", "bytes " + start + "-" + (fileSize - 1) + "/" + fileSize);
                }
                // 设置响应客户端内容类型
                resp.setContentType("application/x-download");
                // 设置响应客户端头
                resp.addHeader("Content-Disposition", "attachment;filename=laolian_client_for_android_v1.0.apk");
                // 当前需要下载文件的大小
                int needSize = (int)responseSize;
                if(start != 0){
                	// 跳已经传输过的字节
                	is.skip(start);
                }
                os = resp.getOutputStream();
                while (needSize > 0) {
                    int len = is.read(buffer);
                    if (needSize < buffer.length) {
                        os.write(buffer, 0, needSize);
                    } else {
                    	os.write(buffer, 0, len);
                        // 如果读取文件大小小于缓冲字节大小，表示已写入完，直接跳出
                        if (len < buffer.length) {
                            break;
                        }
                    }
                    // 不断更新当前可下载文件大小
                    needSize -= buffer.length;
                }
    		} catch (IOException e) {
    			e.printStackTrace();
    			return;
    		} finally {
    			if (is != null)
    				is.close();
    			if (os != null)
    				os.close();
    		}
    	}
    
    	@Override
    	protected void doPost(HttpServletRequest req, HttpServletResponse resp)
    			throws ServletException, IOException {
    		// TODO Auto-generated method stub
    		super.doPost(req, resp);
    		
    	}
    
    }

客户端：

**\[java\]** [ view plain][view plain] [ copy][view plain] [ print][view plain] [?][view plain]

1.  public class TestConn \{  
2.    
3.      /\*\* 
4.       \* @param args 
5.       \* @throws IOException  
6.       \*/  
7.      public static void main(String\[\] args) throws IOException \{  
8.          // TODO Auto-generated method stub  
9.          String urlstr = "http://localhost:8090/mydownload/DownloadServlet";  
10.         URL url = new URL(urlstr);  
11.         HttpURLConnection connection = (HttpURLConnection) url  
12.                 .openConnection();  
13.         connection.setConnectTimeout(5000);  
14.         connection.setRequestMethod("GET");  
15.           
16. //      connection.setRequestProperty("Accept-Encoding", "identity");  
17.         connection.connect();  
18.           
19.         int fileSize = connection.getContentLength();  
20.         System.out.println(connection.getResponseCode());  
21.         System.out.println(fileSize);  
22.         connection.disconnect();  
23.   
24.         download(0, 0, 20000, urlstr);  
25.     \}  
26.       
27.       
28.     private static void download(int startPos, int compeleteSize, int endPos, String urlstr)\{  
29.         HttpURLConnection connection = null;  
30.         RandomAccessFile randomAccessFile = null;  
31.         InputStream is = null;  
32.         try \{  
33.             URL url = new URL(urlstr);  
34.             connection = (HttpURLConnection) url.openConnection();  
35.             connection.setConnectTimeout(5000);  
36.             connection.setRequestMethod("GET");  
37.             // 设置范围，格式为Range：bytes x-y;  
38.             connection.setRequestProperty("Range", "bytes="  
39.                     + (startPos + compeleteSize) + "-" + endPos);  
40.   
41.             randomAccessFile = new RandomAccessFile("/home/agilemobi/Desktop/1.apk", "rwd");  
42.             randomAccessFile.seek(startPos + compeleteSize);  
43.             // 将要下载的文件写到保存在保存路径下的文件中  
44.             is = connection.getInputStream();  
45.             byte\[\] buffer = new byte\[4096\];  
46.             int length = -1;  
47.             while ((length = is.read(buffer)) != -1) \{  
48.                 randomAccessFile.write(buffer, 0, length);  
49.                 compeleteSize += length;  
50.                 System.out.println("compeleteSize:" + compeleteSize);  
51.             \}  
52.             System.out.println("OVER:" + compeleteSize);  
53.         \} catch (Exception e) \{  
54.             e.printStackTrace();  
55.         \} finally \{  
56.             try \{  
57.                 if(is != null)  
58.                     is.close();  
59.                 if(randomAccessFile != null)  
60.                     randomAccessFile.close();  
61.                 if(connection != null)  
62.                     connection.disconnect();  
63.             \} catch (Exception e) \{  
64.                 e.printStackTrace();  
65.             \}  
66.         \}  
67.     \}  
68.   
69. \}

![save_snippets.png][]

public class TestConn {
    
    	/**
    	 * @param args
    	 * @throws IOException 
    	 */
    	public static void main(String[] args) throws IOException {
    		// TODO Auto-generated method stub
    		String urlstr = "http://localhost:8090/mydownload/DownloadServlet";
    		URL url = new URL(urlstr);
    		HttpURLConnection connection = (HttpURLConnection) url
    				.openConnection();
    		connection.setConnectTimeout(5000);
    		connection.setRequestMethod("GET");
    		
    //		connection.setRequestProperty("Accept-Encoding", "identity");
    		connection.connect();
    		
    		int fileSize = connection.getContentLength();
    		System.out.println(connection.getResponseCode());
    		System.out.println(fileSize);
    		connection.disconnect();
    
    		download(0, 0, 20000, urlstr);
    	}
    	
    	
    	private static void download(int startPos, int compeleteSize, int endPos, String urlstr){
    		HttpURLConnection connection = null;
    		RandomAccessFile randomAccessFile = null;
    		InputStream is = null;
    		try {
    			URL url = new URL(urlstr);
    			connection = (HttpURLConnection) url.openConnection();
    			connection.setConnectTimeout(5000);
    			connection.setRequestMethod("GET");
    			// 设置范围，格式为Range：bytes x-y;
    			connection.setRequestProperty("Range", "bytes="
    					+ (startPos + compeleteSize) + "-" + endPos);
    
    			randomAccessFile = new RandomAccessFile("/home/agilemobi/Desktop/1.apk", "rwd");
    			randomAccessFile.seek(startPos + compeleteSize);
    			// 将要下载的文件写到保存在保存路径下的文件中
    			is = connection.getInputStream();
    			byte[] buffer = new byte[4096];
    			int length = -1;
    			while ((length = is.read(buffer)) != -1) {
    				randomAccessFile.write(buffer, 0, length);
    				compeleteSize += length;
    				System.out.println("compeleteSize:" + compeleteSize);
    			}
    			System.out.println("OVER:" + compeleteSize);
    		} catch (Exception e) {
    			e.printStackTrace();
    		} finally {
    			try {
    				if(is != null)
    					is.close();
    				if(randomAccessFile != null)
    					randomAccessFile.close();
    				if(connection != null)
    					connection.disconnect();
    			} catch (Exception e) {
    				e.printStackTrace();
    			}
    		}
    	}
    
    }

关键点：  
客户端

**\[java\]** [ view plain][view plain] [ copy][view plain] [ print][view plain] [?][view plain]

1.  connection.setRequestProperty("Range", "bytes="  
2.                      + (startPos + compeleteSize) + "-" + endPos);

![save_snippets_01.png][]

connection.setRequestProperty("Range", "bytes="
    					+ (startPos + compeleteSize) + "-" + endPos);

**\[java\]** [ view plain][view plain] [ copy][view plain] [ print][view plain] [?][view plain]

1.  RandomAccessFile的使用

![save_snippets.png][]

RandomAccessFile的使用

服务器端

1.对HTTP头Range信息的解析。

2.InputStream的skip()跳过多少字节流。

3.状态的设置。

4.Content-Length的设置，否则客户端getContentLength()返回为-1。

**\[java\]** [ view plain][view plain] [ copy][view plain] [ print][view plain] [?][view plain]

1.  resp.addHeader("Content-Length", "" + (responseSize));

![save_snippets.png][]

resp.addHeader("Content-Length", "" + (responseSize));

顶

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查看评论

4楼 [A232829514][] 2016-09-14 17:00发表 [ \[回复\]][Link 7] [\[引用\]][Link 8] [ \[举报\]][Link 3]

[![3_a232829514.jpg][]][A232829514]

Content-Length: \[文件的总大小\] - \[客户端请求的下载的文件块的开始字节\]  
所以responseSize = end - start ,不是 end - start+1，不然下载的文件与原文件作MD5比较或直接输出大小会发现已经不是同个文件

3楼 [A232829514][] 2016-09-14 16:59发表 [ \[回复\]][Link 7] [\[引用\]][Link 8] [ \[举报\]][Link 3]

[![3_a232829514.jpg][]][A232829514]

2楼 [Java职业不再难][Java] 2015-12-25 12:27发表 [ \[回复\]][Link 7] [\[引用\]][Link 8] [ \[举报\]][Link 3]

[![3_ch2006xa.jpg][]][Java]

好文章

[Link 1]: http://blog.csdn.net/jayqean/article/details/11143971
[Link 2]: http://blog.csdn.net/jayqean/article/details/11143971#comments
[Link 3]: http://blog.csdn.net/jayqean/article/details/11143971#report
[category_icon.jpg]: /images/20220716/6392fe61a3b94a898fae74f36773b6d5.png
[arrow_triangle_20_down.jpg]: http://static.blog.csdn.net/images/arrow_triangle%20_down.jpg
[arrow_triangle_up.jpg]: /images/20220716/41277c0776bf464d9b6ee50ddd0cce35.png
[Link 4]: http://blog.csdn.net/jayqean/article/category/521390
[view plain]: http://blog.csdn.net/jayqean/article/details/11143971#
[save_snippets.png]: /images/20220716/fe841707dfd14ea1aadc95756b115c6c.png
[save_snippets_01.png]: /images/20220716/ecd40a95eb0b4c6381e874d8af8da118.png
[Android Service]: http://blog.csdn.net/jayqean/article/details/7740120
[Link 5]: http://blog.csdn.net/jayqean/article/details/50388580
[http_blog.csdn.net]: http://blog.csdn.net/
[jsp _ java.net.MalformedURLException_ no protocol_ index.jsp_java.net.MalformedURLException_ unknown protocol_ d]: http://blog.csdn.net/jayqean/article/details/5499235
[.class_jar]: http://blog.csdn.net/jayqean/article/details/4518511
[android_java.lang.NoClassDefFoundError]: http://blog.csdn.net/jayqean/article/details/7492382
[java_]: http://blog.csdn.net/jayqean/article/details/4707958
[Link 6]: http://edu.csdn.net/course/detail/865
[Nginx]: http://edu.csdn.net/course/detail/1994
[EasyDarwin]: http://edu.csdn.net/course/detail/2431
[2016]: http://edu.csdn.net/course/detail/2678
[JavaScript]: http://edu.csdn.net/course/detail/2910
[FTP]: http://blog.csdn.net/sunmeng_Alex/article/details/8946253
[orgapachecommonsnetftp_FTP]: http://blog.csdn.net/xuanyuanlei1020/article/details/45578743
[orgapachecommonsnetftp_FTP 1]: http://blog.csdn.net/zqs62761130/article/details/43955319
[orgapachecommonsnetftp_FTP 2]: http://blog.csdn.net/ss19871028/article/details/8933415
[orgapachecommonsnetftp_FTP 3]: http://blog.csdn.net/sam_zhang1984/article/details/7302449
[A232829514]: http://blog.csdn.net/A232829514
[Link 7]: http://blog.csdn.net/jayqean/article/details/11143971#reply
[Link 8]: http://blog.csdn.net/jayqean/article/details/11143971#quote
[3_a232829514.jpg]: /images/20220716/e5cef7513b0b49b5ab9065ecf0bc45c1.png
[Java]: http://blog.csdn.net/ch2006xa
[3_ch2006xa.jpg]: /images/20220716/96b6ad513e3c40459e8bf6e9d20099d6.png