trunk/gora-core/src/main/java/org/apache/gora/util/ReflectionUtils.java

/**
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you under the Apache License, Version 2.0 (the
 * "License"); you may not use this file except in compliance
 * with the License.  You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.apache.gora.util;

import java.lang.reflect.Constructor;
import java.lang.reflect.InvocationTargetException;

/**
 * Utility methods related to reflection
 */
public class ReflectionUtils {

  public static Class<?>[] EMPTY_CLASS_ARRAY = new Class<?>[0];
  public static Object[] EMPTY_OBJECT_ARRAY = new Object[0];
  
  /**
   * Returns the empty argument constructor of the class.
   */
  public static<T> Constructor<T> getConstructor(Class<T> clazz) 
    throws SecurityException, NoSuchMethodException {
    if(clazz == null) {
      throw new IllegalArgumentException("class cannot be null");
    }
    Constructor<T> cons = clazz.getConstructor(EMPTY_CLASS_ARRAY);
    cons.setAccessible(true);
    return cons;
  }
  
  /**
   * Returns whether the class defines an empty argument constructor.
   */
  public static boolean hasConstructor(Class<?> clazz) 
  throws SecurityException, NoSuchMethodException {
    if(clazz == null) {
      throw new IllegalArgumentException("class cannot be null");
    }
    Constructor<?>[] consts = clazz.getConstructors();

    boolean found = false;
    for(Constructor<?> cons : consts) {
      if(cons.getParameterTypes().length == 0) {
        found = true;
      }
    }

    return found;
  }

  /**
   * Constructs a new instance of the class using the no-arg constructor.
   * @param clazz the class of the object
   * @return a new instance of the object
   */
  public static <T> T newInstance(Class<T> clazz) throws InstantiationException
  , IllegalAccessException, SecurityException, NoSuchMethodException
  , IllegalArgumentException, InvocationTargetException {
    
    Constructor<T> cons = getConstructor(clazz);
    
    return cons.newInstance(EMPTY_OBJECT_ARRAY);
  }
  
  /**
   * Constructs a new instance of the class using the no-arg constructor.
   * @param classStr the class name of the object
   * @return a new instance of the object
   */
  public static Object newInstance(String classStr) throws InstantiationException
    , IllegalAccessException, ClassNotFoundException, SecurityException
    , IllegalArgumentException, NoSuchMethodException, InvocationTargetException {
    if(classStr == null) {
      throw new IllegalArgumentException("class cannot be null");
    }
    Class<?> clazz = ClassLoadingUtils.loadClass(classStr);
    return newInstance(clazz);
  }
  
  /**
   * Returns the value of a named static field
   */
  public static Object getStaticField(Class<?> clazz, String fieldName) 
  throws IllegalArgumentException, SecurityException,
  IllegalAccessException, NoSuchFieldException {
    
    return clazz.getField(fieldName).get(null);
  }
}