code: public static void initSystemProperties() {
  
          String implName;
          // initialize system properties
          if (System.getProperty(SAX_PARSER_FACTORY_KEY) == null) {
              implName = SAXParserFactory.newInstance().getClass().getName();
              LOG.info("Setting sax parser factory impl property to " + implName);
              System.setProperty(SAX_PARSER_FACTORY_KEY, implName);
          }
          if (System.getProperty(XML_READER_KEY) == null) {
              SAXReader reader = new SAXReader();
              try {
                  implName = reader.getXMLReader().getClass().getName();
                  LOG.info("Setting xml reader impl property to " + implName);
                  System.setProperty(XML_READER_KEY, implName);
              } catch (SAXException e) {
                  LOG.error("Error evaluating XMLReader impl.", e);
              }
          }
          if (System.getProperty(SAX_PARSER_CONFIG_KEY) == null) {
              ParserImpl saxParser = new ParserImpl();
              implName = saxParser.getConfigImplName();
              if (implName != null) {
                  LOG.info("Setting xml parser configuration impl property to " + implName);
                  System.setProperty(SAX_PARSER_CONFIG_KEY, implName);
              }
          }
      }
docs: Initializes XML processing system properties to avoid evaluating the XML parser and reader implementation each time an XML document is read.<p>
  This is done for performance improvements only.<p>