HITANGJUN BLOG

 public String readFile(){
 
	   long start = System.currentTimeMillis();
	   //open virtual dir file in cloud 
	   mongodbfile cloudStore = new mongodbfile();
	   BufferedOutputStream bos = null;
	   String fileId = "";
	   getResponse().reset();
	   getResponse().resetBuffer();
	   int bufferSize = 1024;
	   getResponse().setBufferSize(bufferSize);
	   try {
		 getResponse().setContentType("image/");//请相应修改
		 getResponse().setHeader("Accept-Ranges", "bytes");
		   log.debug("readCloudStoreFile fileId = {}",fileId);
		   int readResult = cloudStore.ReadBegin(fileId);
		   if(readResult == 0){//文件读取成功
			   long contentLength = cloudStore.GetFileLength(fileId);
                           //模拟Etag的信息
			   getResponse().setHeader("Etag", "W/\""+contentLength+"-1316052976000\"");
			   getResponse().setHeader("Last-Modified", "Thu, 15 Sep 2011 02:16:16 GMT");
			   byte[] buffer = new byte[bufferSize];
			   bos = new BufferedOutputStream(getResponse().getOutputStream());
			   long pos = 0;			   
			   ArrayList ranges = null;			   
			   long s = System.currentTimeMillis();
			   // Parse range specifier
                           ranges = parseRange(request, response, contentLength);
                           long requestLength = 0;			 
               if ( (((ranges == null) || (ranges.isEmpty()))
                               && (request.getHeader("Range") == null) )
                       || (ranges == FULL) ){
 
            	   if (contentLength < Integer.MAX_VALUE) {
    				   getResponse().setContentLength((int) contentLength);
                   } else {
                       // Set the content-length as String to be able to use a long
                	   getResponse().setHeader("content-length", "" + contentLength);
                   }
            	   requestLength = contentLength;
               }else{
		// 若客户端传来Range，说明之前下载了一部分，设置206状态(SC_PARTIAL_CONTENT)
				   getResponse().setStatus(HttpServletResponse.SC_PARTIAL_CONTENT);
 
				   log.debug("=======ranges.size() {}",ranges.size());
				   if (ranges.size() == 1) {
 
		                Range range = (Range) ranges.get(0);
		                response.addHeader("Content-Range", "bytes "
		                                   + range.start
		                                   + "-" + range.end + "/"
		                                   + range.length);
		                log.debug("Content-Range:  {}","bytes "
                                + range.start
                                + "-" + range.end + "/"
                                + range.length);
 
//重点在这里对实时请求的数据长度和数据流剩余长度，和写回Response数据长度的判断
		                long length = range.end - range.start + 1;
		                if (length < Integer.MAX_VALUE) {
		                    response.setContentLength((int) length);
		                } else {
		                    // Set the content-length as String to be able to use a long
		                    response.setHeader("content-length", "" + length);
		                }
		                log.debug("request range length = {}",length);    
		                pos = range.start;
		                requestLength = length;
		            } else {
                                //这里未处理range数组的情况
		                response.setContentType("multipart/byteranges; boundary="
		                                        + mimeSeparation);
	                    log.warn("@@@@@@@@@@@ for multipart transfer todo");
		            }   
			   }
               log.debug("###########skip pos = {}",pos);
			   if (pos != 0) {
				   // 略过已经传输过的字节
				   long sk = System.currentTimeMillis();
				   cloudStore.Skip(pos);				  
			   }
			   long ws = System.currentTimeMillis();
			   if(requestLength < bufferSize){
				   bufferSize = (int)requestLength;
			   }
 
			   int readedLen = 0;
			   for(long len = 0;len<requestLength;){
				   readedLen = cloudStore.Read(buffer, bufferSize);
				   bos.write(buffer,0,readedLen);
				   len+=readedLen;
			   }
 
			   bos.flush();
			   log.debug("write data spent {}",System.currentTimeMillis()-ws);
		   }
 
		   log.debug("write to response file success fileId = {}",fileId);
	   } catch (Exception e) {
 
	   }finally{
		   //关闭资源	   
	   return null;
   }
 
        /**
	 * MIME multipart separation string
	 */
	protected static final String mimeSeparation = "CATALINA_MIME_BOUNDARY";
 
   /**
    * Full range marker.
    */
   protected static ArrayList FULL = new ArrayList();
 
   /**
    * Parse the range header.
    *
    * @param request The servlet request we are processing
    * @param response The servlet response we are creating
    * @return Vector of ranges
    */
   protected ArrayList parseRange(HttpServletRequest request,
                               HttpServletResponse response,long length)
       throws IOException {
 
       // Checking If-Range
       String headerValue = request.getHeader("If-Range");
       log.debug("headerValue = ",headerValue);
       if (headerValue != null) {
 
           long headerValueTime = (-1L);
           try {
               headerValueTime = request.getDateHeader("If-Range");
           } catch (IllegalArgumentException e) {
               ;
           }
 
           String eTag = "W/\""+length+"-1316052976000\"";
           long lastModified = 1316052976000L;
 
           log.debug("headerValueTime = ",headerValueTime);
           if (headerValueTime == (-1L)) {
 
               // If the ETag the client gave does not match the entity
               // etag, then the entire entity is returned.
               if (!eTag.equals(headerValue.trim())){
            	   log.debug("If the ETag the client gave does not match the entity etag, "
                            +"then the entire entity is returned.");
            	   return FULL;
               }
           } else {
 
               // If the timestamp of the entity the client got is older than
               // the last modification date of the entity, the entire entity
               // is returned.
               if (lastModified > (headerValueTime + 1000)){
            	   log.debug("If the timestamp of the entity the client got is older "
            +"than the last modification date of the entity, the entire entity is returned");
            	   return FULL;
 
               }
           }
 
       }
 
       long fileLength = length;
 
       if (fileLength == 0)
           return null;
 
       // Retrieving the range header (if any is specified
       String rangeHeader = request.getHeader("Range");
 
       log.debug("rangeHeader = ",rangeHeader);
       if (rangeHeader == null){
    	   return null;
       }    
       // bytes is the only range unit supported (and I don't see the point
       // of adding new ones).
       if (!rangeHeader.startsWith("bytes")) {
           response.addHeader("Content-Range", "bytes */" + fileLength);
           response.sendError
               (HttpServletResponse.SC_REQUESTED_RANGE_NOT_SATISFIABLE);
           return null;
       }
 
       rangeHeader = rangeHeader.substring(6);
 
       // Vector which will contain all the ranges which are successfully
       // parsed.
       ArrayList<range> result = new ArrayList</range><range>();
       StringTokenizer commaTokenizer = new StringTokenizer(rangeHeader, ",");
 
       // Parsing the range list
       while (commaTokenizer.hasMoreTokens()) {
           String rangeDefinition = commaTokenizer.nextToken().trim();
 
           Range currentRange = new Range();
           currentRange.length = fileLength;
 
           int dashPos = rangeDefinition.indexOf('-');
 
           if (dashPos == -1) {
               response.addHeader("Content-Range", "bytes */" + fileLength);
               response.sendError
                   (HttpServletResponse.SC_REQUESTED_RANGE_NOT_SATISFIABLE);
               return null;
           }
 
           if (dashPos == 0) {
 
               try {
                   long offset = Long.parseLong(rangeDefinition);
                   currentRange.start = fileLength + offset;
                   currentRange.end = fileLength - 1;
               } catch (NumberFormatException e) {
                   response.addHeader("Content-Range",
                                      "bytes */" + fileLength);
                   response.sendError
                       (HttpServletResponse
                        .SC_REQUESTED_RANGE_NOT_SATISFIABLE);
                   return null;
               }
 
           } else {
 
               try {
                   currentRange.start = Long.parseLong
                       (rangeDefinition.substring(0, dashPos));
                   if (dashPos < rangeDefinition.length() - 1)
                       currentRange.end = Long.parseLong
                           (rangeDefinition.substring
                            (dashPos + 1, rangeDefinition.length()));
                   else
                       currentRange.end = fileLength - 1;
               } catch (NumberFormatException e) {
                   response.addHeader("Content-Range",
                                      "bytes */" + fileLength);
                   response.sendError
                       (HttpServletResponse
                        .SC_REQUESTED_RANGE_NOT_SATISFIABLE);
                   return null;
               }
 
           }
 
           if (!currentRange.validate()) {
               response.addHeader("Content-Range", "bytes */" + fileLength);
               response.sendError
                   (HttpServletResponse.SC_REQUESTED_RANGE_NOT_SATISFIABLE);
               return null;
           }
 
           result.add(currentRange);
       }
 
       return result;
   }
 
   // ------------------------------------------------------ Range Inner Class
 
 
   protected class Range {
 
       public long start;
       public long end;
       public long length;
 
       /**
        * Validate range.
        */
       public boolean validate() {
           if (end >= length)
               end = length - 1;
           return ( (start >= 0) && (end >= 0) && (start < = end)
                    && (length > 0) );
       }
 
       public void recycle() {
           start = 0;
           end = 0;
           length = 0;
       }
 
   }
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