java 断点续传文件下载（服务端）

    public static void ddxcFile(HttpServletRequest request, HttpServletResponse response, File file)throws Exception{
        BufferedInputStream bis = null;
        try {
            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");

                Enumeration<String> headerNames = request.getHeaderNames();
                while (headerNames.hasMoreElements()){
                    String s = headerNames.nextElement();
                    logger.info("{} : {}", s, request.getHeader(s));
                }
                // client requests a file block download start byte
                String range = request.getHeader("Range");
                logger.info(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", Long.toString(contentLength));

                // 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);
                }

                //获取content type
                String contentType = new MimetypesFileTypeMap().getContentType(file);
                response.setContentType(contentType);
                
                response.addHeader("Content-Disposition", "attachment;filename=" + file.getName());

                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.getName() + " not found.");
                }
            }
        } catch (IOException ie) {
            if (ie instanceof ClientAbortException){
                logger.error("客户端已关闭");
            }else {
                throw ie;
            }
        }
    }

Tags：断点续传

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