code: public Charset readCharset() {
          BasicProperties basicProperties = message.getBasicProperties();
          if (basicProperties == null) {
              return Message.DEFAULT_MESSAGE_CHARSET;
          }
          String contentCharset = basicProperties.getContentEncoding();
          if (contentCharset == null) {
              return Message.DEFAULT_MESSAGE_CHARSET;
          }
          return Charset.forName(contentCharset);
      }
docs: Extracts the message body's charset encoding
  by looking it up in the message properties if
  given there and choosing the default charset (UTF-8)
  otherwise.
  
  @return The message body's charset encoding