athrunwang

File file = new File(location);                        
                        if (file.exists()) {                                        
                            long p = 0;
                            long fileLength;
                            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
                            if (request.getHeader("Range") != null) {                                
                                response.setStatus(javax.servlet.http.HttpServletResponse.SC_PARTIAL_CONTENT);
                                p = Long.parseLong(request.getHeader("Range")
                                        .replaceAll("bytes=", "")
                                        .replaceAll("-", "")
                                        );                                
                            }
                            // support multi-threaded download
                            // respone format:
                            // Content-Length:[file size] - [client request start bytes from file block]
                            response.setHeader("Content-Length", new Long(fileLength - p).toString());
                            
                            if (p != 0) {
                                // 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]
                                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);
                                // pointer move to seek
                                bis.skip(p);
                            }
                            
                            String fileName = file.getName();
                            response.addHeader("Content-Disposition", "attachment;filename=" + fileName);
                                         
                            while ((size = bis.read(buf)) != -1) {
                                response.getOutputStream().write(buf,0,size);
                                response.getOutputStream().flush();                                
                            }
                            bis.close();

public class TestDownload {

    /**
     * @param args
     */
    public static void main(String[] args) {
        // TODO Auto-generated method stub
        HttpURLConnection httpURLConnection = null;
        URL url = null;
        BufferedInputStream bis = null;
        byte[] buf = new byte[10240];
        int size = 0;
        String fileName = "aaa.zip";
        String filePath = "C:\\Users\\Desktop";
        String remoteUrl = "http://127.0.0.1:8080/down.zip";

        // 检查本地文件
        RandomAccessFile rndFile = null;
        File file = new File(filePath + "\\" + fileName);
        long remoteFileSize = getRemoteFileSzie(remoteUrl);
        long nPos = 0;
       
        if (file.exists()) {                       
            long localFileSzie = file.length();
            if (localFileSzie < remoteFileSize) {                   
                System.out.println("文件续传...");
                nPos = localFileSzie;
            } else {
                System.out.println("文件存在，重新下载...");
                file.delete();
                try {
                    file.createNewFile();
                } catch (Exception e) {
                    // TODO: handle exception
                    e.printStackTrace();
                }   
            }
           
        } else {
            // 建立文件
            try {
                file.createNewFile();
            } catch (Exception e) {
                // TODO: handle exception
                e.printStackTrace();
            }           
        }
       
        // 下载文件
        try {
            url = new URL(remoteUrl);       
            httpURLConnection = (HttpURLConnection)url.openConnection();
            // 设置User-Agent
            httpURLConnection.setRequestProperty("User-Agent", "Net");
            // 设置续传开始
            httpURLConnection.setRequestProperty("Range", "bytes=" + nPos + "-");
            // 获取输入流
            bis = new BufferedInputStream(httpURLConnection.getInputStream());           
            rndFile = new RandomAccessFile(filePath + "\\" + fileName, "rw");
            rndFile.seek(nPos);
            int i = 0;
            while ((size = bis.read(buf)) != -1) {
                //if (i > 500) break;               
                rndFile.write(buf, 0, size);
               
                i++;
            }
            System.out.println("i=" + i);
            httpURLConnection.disconnect();
        } catch (Exception e) {
            // TODO: handle exception
            e.printStackTrace();
        }
    }

    public static long getRemoteFileSzie(String url) {
        long size = 0;
        try {
            HttpURLConnection httpUrl = (HttpURLConnection)(new URL(url)).openConnection();
            size = httpUrl.getContentLength();
            httpUrl.disconnect();           
        } catch (Exception e) {
            // TODO: handle exception
            e.printStackTrace();
        }
        return size;
    }
}