Java 下載支持斷點續傳服務端

 
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,從頭開始的全文下載；1,從某字節開始的下載（bytes=27000-）；2,從某字節開始到某字節結束的下載（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;  // 客戶端請求的是270000之后的字節（包括bytes下標索引為270000的字節）
            } 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; // 客戶端請求的是 270000-320000 之間的字節
            }
        } else {
            contentLength = fileLength;
        }

        // 如果設設置了Content-Length，則客戶端會自動進行多線程下載。如果不希望支持多線程，則不要設置這個參數。
        // Content-Length: [文件的總大小] - [客戶端請求的下載的文件塊的開始字節]
        response.setHeader("Content-Length", new Long(contentLength).toString());

        // 斷點開始
        // 響應的格式是:
        // Content-Range: bytes [文件塊的開始字節]-[文件的總大小 - 1]/[文件的總大小]
        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) {
            // 針對 bytes=27000-39000 的請求，從27000開始寫數據                    
            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 之類的異常
} catch (Exception e) {
    logger.error(e);
}

}
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