java 断点续传文件下载（服务端）

最近做个下载类的小项目，记录一下java 多线程断点续传下载工具类。

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;            }        }    }