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  package org.apache.cayenne.ejbql;
  
  /**
   * Creates {@link EJBQLParser} based on the system settings.
   * 
   * @since 3.0
   */
  public class EJBQLParserFactory {
  
      // this is the parser generated by JJTree/JavaCC
      private static String DEFAULT_PARSER_CLASS = "org.apache.cayenne.ejbql.parser.EJBQL$EJBQLDefaultParser";
  
      private static Class parserClass;
  
      private static Class getParserClass() throws ClassNotFoundException {
          if (parserClass == null) {
              // for now support only the default parser. If needed it should be
              // easy to plug external parsers via a System property...
              parserClass = Class.forName(DEFAULT_PARSER_CLASS, true, Thread
                      .currentThread()
                      .getContextClassLoader());
          }
  
          return parserClass;
      }
  
      public static EJBQLParser getParser() throws EJBQLException {
          try {
              return (EJBQLParser) getParserClass().getDeclaredConstructor().newInstance();
          }
          catch (Exception e) {
              throw new EJBQLException("Error creating EJBQL parser", e);
          }
      }
  }
  