code: private String getContentType(String dataHeader) {
  		String token = "Content-Type:";
  		int start = dataHeader.indexOf(token);
  		if (start == -1) {
  			return StrUtil.EMPTY;
  		}
  		start += token.length();
  		return dataHeader.substring(start);
  	}
docs: 头信息中获得content type
  
  @param dataHeader data header string
  @return content type or an empty string if no content type defined