docs: public static String filter( String message ) {
  
          if (message == null) {
              return (null);
          }
  
          char content[] = new char[message.length()];
          message.getChars(0, message.length(), content, 0);
          StringBuilder result = new StringBuilder(content.length + 50);
          for (int i = 0; i < content.length; i++) {
              switch (content[i]) {
                  case '<':
                      result.append("&lt;");
                      break;
                  case '>':
                      result.append("&gt;");
                      break;
                  case '&':
                      result.append("&amp;");
                      break;
                  case '"':
                      result.append("&quot;");
                      break;
                  default:
                      result.append(content[i]);
              }
          }
          return (result.toString());
  
      }