java 下载 断点续传
1 import java.io.BufferedInputStream;2 import java.io.File;
3 import java.io.FileInputStream;
4 import java.io.IOException;
5 import java.io.InputStream;
6 import java.io.OutputStream;
7
8 import javax.servlet.ServletException;
9 import javax.servlet.http.HttpServlet;
10 import javax.servlet.http.HttpServletRequest;
11 import javax.servlet.http.HttpServletResponse;
12
13
14 public class DownLoad extends HttpServlet {
15 @Override
16 protected void service(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
17 String location = "E:\\upload\\1.rar";
18 downFile(response,request, location);
19
20 }
21 private void downFile(HttpServletResponse response, HttpServletRequest request, String location){
22 BufferedInputStream bis = null;
23 try {
24 File file = new File(location);
25 if (file.exists()) {
26 long p = 0L;
27 long toLength = 0L;
28 long contentLength = 0L;
29 int rangeSwitch = 0; // 0,从头开始的全文下载；1,从某字节开始的下载（bytes=27000-）；2,从某字节开始到某字节结束的下载（bytes=27000-39000）
30 long fileLength;
31 String rangBytes = "";
32 fileLength = file.length();
33
34 // get file content
35 InputStream ins = new FileInputStream(file);
36 bis = new BufferedInputStream(ins);
37
38 // tell the client to allow accept-ranges
39 response.reset();
40 response.setHeader("Accept-Ranges", "bytes");
41
42 // client requests a file block download start byte
43 String range = request.getHeader("Range");
44 if (range != null && range.trim().length() > 0 && !"null".equals(range)) {
45 response.setStatus(javax.servlet.http.HttpServletResponse.SC_PARTIAL_CONTENT);
46 rangBytes = range.replaceAll("bytes=", "");
47 if (rangBytes.endsWith("-")) { // bytes=270000-
48 rangeSwitch = 1;
49 p = Long.parseLong(rangBytes.substring(0, rangBytes.indexOf("-")));
50 contentLength = fileLength - p; // 客户端请求的是270000之后的字节（包括bytes下标索引为270000的字节）
51 } else { // bytes=270000-320000
52 rangeSwitch = 2;
53 String temp1 = rangBytes.substring(0, rangBytes.indexOf("-"));
54 String temp2 = rangBytes.substring(rangBytes.indexOf("-") + 1, rangBytes.length());
55 p = Long.parseLong(temp1);
56 toLength = Long.parseLong(temp2);
57 contentLength = toLength - p + 1; // 客户端请求的是 270000-320000 之间的字节
58 }
59 } else {
60 contentLength = fileLength;
61 }
62
63 // 如果设设置了Content-Length，则客户端会自动进行多线程下载。如果不希望支持多线程，则不要设置这个参数。
64 // 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]
65 response.setHeader("Content-Length", new Long(contentLength).toString());
66
67 // 断点开始
68 // 响应的格式是:
69 // Content-Range: bytes [文件块的开始字节]-[文件的总大小 - 1]/[文件的总大小]
70 if (rangeSwitch == 1) {
71 String contentRange = new StringBuffer("bytes ").append(new Long(p).toString()).append("-")
72 .append(new Long(fileLength - 1).toString()).append("/")
73 .append(new Long(fileLength).toString()).toString();
74 response.setHeader("Content-Range", contentRange);
75 bis.skip(p);
76 } else if (rangeSwitch == 2) {
77 String contentRange = range.replace("=", " ") + "/" + new Long(fileLength).toString();
78 response.setHeader("Content-Range", contentRange);
79 bis.skip(p);
80 } else {
81 String contentRange = new StringBuffer("bytes ").append("0-")
82 .append(fileLength - 1).append("/")
83 .append(fileLength).toString();
84 response.setHeader("Content-Range", contentRange);
85 }
86
87 String fileName = file.getName();
88 response.setContentType("application/octet-stream");
89 response.addHeader("Content-Disposition", "attachment;filename=" + fileName);
90
91 OutputStream out = response.getOutputStream();
92 int n = 0;
93 long readLength = 0;
94 int bsize = 1024;
95 byte[] bytes = new byte[bsize];
96 if (rangeSwitch == 2) {
97 // 针对 bytes=27000-39000 的请求，从27000开始写数据
98 while (readLength <= contentLength - bsize) {
99 n = bis.read(bytes);
100 readLength += n;
101 out.write(bytes, 0, n);
102 }
103 if (readLength <= contentLength) {
104 n = bis.read(bytes, 0, (int) (contentLength - readLength));
105 out.write(bytes, 0, n);
106 }
107 } else {
108 while ((n = bis.read(bytes)) != -1) {
109 out.write(bytes,0,n);
110 }
111 }
112 out.flush();
113 out.close();
114 bis.close();
115 } else {
116 System.out.println(" location + not found");
117 }
118 } catch (IOException ie) {
119 } catch (Exception e) {
120 e.printStackTrace();
121
122 }
123 }
124 }
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