Java 下载支持断点续传服务端详解编程语言

  
private void downFile(HttpServletResponse response, HttpServletRequest request, String location){ 
    BufferedInputStream bis = null; 
    try { 
        File file = new File(location); 
        if (file.exists()) { 
            long p = 0L; 
            long toLength = 0L; 
            long contentLength = 0L; 
            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） 
            long fileLength; 
            String rangBytes = ""; 
            fileLength = file.length(); 
 
            // get file content 
            InputStream ins = new FileInputStream(file); 
            bis = new BufferedInputStream(ins); 
 
            // tell the client to allow accept-ranges 
            response.reset(); 
            response.setHeader("Accept-Ranges", "bytes"); 
 
            // client requests a file block download start byte 
            String range = request.getHeader("Range"); 
            if (range != null && range.trim().length() > 0 && !"null".equals(range)) { 
                response.setStatus(javax.servlet.http.HttpServletResponse.SC_PARTIAL_CONTENT); 
                rangBytes = range.replaceAll("bytes=", ""); 
                if (rangBytes.endsWith("-")) {  // bytes=270000- 
                    rangeSwitch = 1; 
                    p = Long.parseLong(rangBytes.substring(0, rangBytes.indexOf("-"))); 
                    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） 
                } else { // bytes=270000-320000 
                    rangeSwitch = 2; 
                    String temp1 = rangBytes.substring(0, rangBytes.indexOf("-")); 
                    String temp2 = rangBytes.substring(rangBytes.indexOf("-") + 1, rangBytes.length()); 
                    p = Long.parseLong(temp1); 
                    toLength = Long.parseLong(temp2); 
                    contentLength = toLength - p + 1; // 客户端请求的是 270000-320000 之间的字节 
                } 
            } else { 
                contentLength = fileLength; 
            } 
 
            // 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。 
            // 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] 
            response.setHeader("Content-Length", new Long(contentLength).toString()); 
 
            // 断点开始 
            // 响应的格式是: 
            // Content-Range: bytes [文件块的开始字节]-[文件的总大小 - 1]/[文件的总大小] 
            if (rangeSwitch == 1) { 
                String contentRange = new StringBuffer("bytes ").append(new Long(p).toString()).append("-") 
                        .append(new Long(fileLength - 1).toString()).append("/") 
                        .append(new Long(fileLength).toString()).toString(); 
                response.setHeader("Content-Range", contentRange); 
                bis.skip(p); 
            } else if (rangeSwitch == 2) { 
                String contentRange = range.replace("=", " ") + "/" + new Long(fileLength).toString(); 
                response.setHeader("Content-Range", contentRange); 
                bis.skip(p); 
            } else { 
                String contentRange = new StringBuffer("bytes ").append("0-") 
                        .append(fileLength - 1).append("/") 
                        .append(fileLength).toString(); 
                response.setHeader("Content-Range", contentRange); 
            } 
 
            String fileName = file.getName(); 
            response.setContentType("application/octet-stream"); 
            response.addHeader("Content-Disposition", "attachment;filename=" + fileName); 
 
            OutputStream out = response.getOutputStream(); 
            int n = 0; 
            long readLength = 0; 
            int bsize = 1024; 
            byte[] bytes = new byte[bsize]; 
            if (rangeSwitch == 2) { 
                // 针对 bytes=27000-39000 的请求，从27000开始写数据                     
                while (readLength <= contentLength - bsize) { 
                    n = bis.read(bytes); 
                    readLength += n; 
                    out.write(bytes, 0, n); 
                } 
                if (readLength <= contentLength) { 
                    n = bis.read(bytes, 0, (int) (contentLength - readLength)); 
                    out.write(bytes, 0, n); 
                }                    
            } else { 
                while ((n = bis.read(bytes)) != -1) { 
                    out.write(bytes,0,n);                                                       
                }                    
            } 
            out.flush(); 
            out.close(); 
            bis.close(); 
        } else { 
            if (logger.isDebugEnabled()) { 
                logger.debug("Error: file " + location + " not found."); 
            }                 
        } 
    } catch (IOException ie) { 
        // 忽略 ClientAbortException 之类的异常 
    } catch (Exception e) { 
        logger.error(e); 
    } 
}