code: public void beforeClosingBrace(StringBuilder sb, boolean pretty, String indent, String... attributeNames) {
          StringWriter writer = new StringWriter();
          beforeClosingBrace(pretty, indent, writer);
          sb.append(writer.toString());
      }
docs: Override in subclasses in order to inject custom content into Json just before the closing brace.
  
  <p>To keep the formatting, it is recommended to implement this method as the example below.
  
  <blockquote><pre>
  sb.append(',');
  if (pretty) { sb.append('\n').append(indent); }
  sb.append("\"test\":\"...\"");
  </pre></blockquote>
  
  @param sb to write custom content to
  @param pretty pretty format (human readable), or one line text.
  @param indent indent at current level
  @param attributeNames list of attributes to include