code: private HttpResponse sendRedirectIfPosible() {
  		if (this.maxRedirectCount < 1) {
  			// 不重定向
  			return null;
  		}
  
  		// 手动实现重定向
  		if (this.httpConnection.getHttpURLConnection().getInstanceFollowRedirects()) {
  			int responseCode;
  			try {
  				responseCode = httpConnection.responseCode();
  			} catch (IOException e) {
  				throw new HttpException(e);
  			}
  			if (responseCode != HttpURLConnection.HTTP_OK) {
  				if (responseCode == HttpURLConnection.HTTP_MOVED_TEMP || responseCode == HttpURLConnection.HTTP_MOVED_PERM || responseCode == HttpURLConnection.HTTP_SEE_OTHER) {
  					this.url = httpConnection.header(Header.LOCATION);
  					if (redirectCount < this.maxRedirectCount) {
  						redirectCount++;
  						return execute();
  					} else {
  						StaticLog.warn("URL [{}] redirect count more than two !", this.url);
  					}
  				}
  			}
  		}
  		return null;
  	}
docs: 调用转发，如果需要转发返回转发结果，否则返回<code>null</code>
  
  @return {@link HttpResponse}，无转发返回 <code>null</code>