Java 实现的断点下载

• HttpServletRequest / Response
• HttpClient
• ServletOutputStream
• BufferedInputStream

    /** 
         * @desc 断点下载工具方法 
         * @param request 
         * @param response 
         * @param fileLength 
         * @param contentType 
         * @param fileName 
         * @param fileId 
         */  
        public static void resumeDownload(HttpServletRequest request,HttpServletResponse response,Long fileLength,String contentType,String fileName,String fileId) {  
            ServletOutputStream out = null;  
            response.reset();  
      
            // 记录断点续传的开始点  
            long pos = 0;  
            if (null != request.getHeader("Range")) {  
                response.setStatus(HttpServletResponse.SC_PARTIAL_CONTENT);  
                try {  
                    pos = Long.parseLong(request.getHeader("Range")  
                            .replaceAll("bytes=","").replaceAll("-.*",""));  
                } catch (NumberFormatException e) {  
                    LOGGER.error(e.getMessage(),e);  
                    pos = 0;  
                }  
                String contentRange = new StringBuffer("bytes ").append(pos + "")  
                        .append("-").append((fileLength.intValue() - 1) + "")  
                        .append("/").append(fileLength.intValue() + "").toString();  
                response.setHeader("Content-Range",contentRange);  
            }  
      
            response.setHeader("Accept-Ranges","bytes");  
            response.setHeader("Content-Length",String.valueOf(fileLength.intValue() - pos));  
            response.setCharacterEncoding("UTF-8");  
            response.setContentType(contentType);  
            response.setHeader("Content-disposition","attachment;filename=""  
                    + fileName + """);  
            try {  
                out = response.getOutputStream();  
            } catch (IOException e) {  
                LOGGER.error(e.getMessage(),e);  
            }  
      
            // 断点下载  
            CloseableHttpClient httpClient = HttpClients.createDefault();  
      
            HttpPost httpPost = new HttpPost(SysConf.getString("fezo.download.url"));  
      
            List<NameValuePair> nvps = new ArrayList<NameValuePair>();  
            nvps.add(new BasicNameValuePair(SysConf.getString("fezo.download.param"),fileId));  
              
            HttpResponse httpResponse = null;  
            BufferedInputStream input = null;  
            try {  
                httpPost.setEntity(new UrlEncodedFormEntity(nvps));  
                  
                httpPost.setHeader("Range","bytes=" + pos + "-");  
                httpResponse = httpClient.execute(httpPost);  
      
                input = new BufferedInputStream(httpResponse.getEntity().getContent());  
      
                byte[] buffer = new byte[CommonConstants.BUFFER_SIZE];  
                int len = -1;  
                while ((len = input.read(buffer)) != -1) {  
                    out.write(buffer,len);  
                }  
                out.flush();  
                out.close();  
                input.close();  
            } catch (UnsupportedEncodingException e) {  
                LOGGER.error(e.getMessage(),e);  
            } catch (ClientProtocolException e) {  
                LOGGER.error(e.getMessage(),e);  
            } catch (IOException e) {  
                // 可以忽略这个异常，有可能是用户暂停下载，或者迅雷等下载工具分块下载  
            } finally {  
                try {  
                    if (httpClient != null) httpClient.close();  
                } catch(IOException e) {  
                    LOGGER.error(e.getMessage(),e);  
                }  
            }  
        }  

>>>点击这里下载代码
4. 重点与难点 ??? - 迅雷等多线程分块下载客户端下载的处理：还是要处理好"Range" 和 "Conent-Range" 等头部信息，迅雷会自动将文件内容分块、记录起始位置。

来自：http://blog.csdn.net/alli0968/article/details/47337349