code: /* LanguageTool, a natural language style checker
   * Copyright (C) 2014 Daniel Naber (http://www.danielnaber.de)
   *
   * This library is free software; you can redistribute it and/or
   * modify it under the terms of the GNU Lesser General Public
   * License as published by the Free Software Foundation; either
   * version 2.1 of the License, or (at your option) any later version.
   *
   * This library is distributed in the hope that it will be useful,
   * but WITHOUT ANY WARRANTY; without even the implied warranty of
   * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
   * Lesser General Public License for more details.
   *
   * You should have received a copy of the GNU Lesser General Public
   * License along with this library; if not, write to the Free Software
   * Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301
   * USA
   */
  package org.languagetool.rules.patterns;
  
  import org.languagetool.JLanguageTool;
  
  import java.lang.reflect.Constructor;
  
  /**
   * Create a {@link RuleFilter}.
   * @since 2.7 (public since 3.2)
   */
  public class RuleFilterCreator {
  
    /**
     * @param className fully qualified class Name of a class implementing {@link RuleFilter}
     */
    public RuleFilter getFilter(String className) {
      try {
        Class<?> aClass = JLanguageTool.getClassBroker().forName(className);
        Constructor<?>[] constructors = aClass.getConstructors();
        if (constructors.length != 1) {
          throw new RuntimeException("Constructor of filter class '"
                  + className + "' must have exactly one constructor, but it has " + constructors.length);
        }
        Constructor<?> constructor = constructors[0];
        try {
          if (constructor.getParameterTypes().length != 0) {
            throw new RuntimeException("Constructor of filter class '" + className + "' must not have arguments: " + constructor);
          }
          Object filter = constructor.newInstance();
          if (filter instanceof RuleFilter) {
            return (RuleFilter) filter;
          } else {
            throw new RuntimeException("Filter class '" + className + "' must implement interface " + RuleFilter.class.getSimpleName());
          }
        } catch (Exception e) {
          throw new RuntimeException("Could not create filter class using constructor " + constructor, e);
        }
      } catch (ClassNotFoundException e) {
        throw new RuntimeException("Could not find filter class: '"
                + className + "' - make sure to use a fully qualified class name like 'org.languagetool.rules.MyFilter'");
      }
    }
   
  }
  