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 }