Property access utility methods : Properties « Collections « Java Tutorial

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3. Properties

/*
 * Copyright 2004, 2005, 2006 Odysseus Software GmbH
 *
 * Licensed 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.
 */ 

import java.util.Collections;
import java.util.HashMap;
import java.util.Iterator;
import java.util.Map;

import java.beans.BeanInfo;
import java.beans.IntrospectionException;
import java.beans.Introspector;
import java.beans.PropertyDescriptor;

import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;

/**
 * Property access utility methods.
 *
 * @author Christoph Beck
 */
public class PropertyUtils {
  private static HashMap descriptorCache = new HashMap();

  /**
   * Get map with property descriptors for the specified bean class
   */
  private static Map getPropertyDescriptors(Class clazz) {
    HashMap map = (HashMap)descriptorCache.get(clazz);
    if (map == null) {
      BeanInfo beanInfo = null;
      try {
        beanInfo = Introspector.getBeanInfo(clazz);
      } catch (IntrospectionException e) {
        return Collections.EMPTY_MAP;
      }
      PropertyDescriptor[] descriptors = beanInfo.getPropertyDescriptors();
      if (descriptors == null)
         descriptors = new PropertyDescriptor[0];
      map = new HashMap(descriptors.length);
      for (int i = 0; i < descriptors.length; i++)
        map.put(descriptors[i].getName(), descriptors[i]);
      descriptorCache.put(clazz, map);
    }
    return map;
  }

  /**
   * Get property names of the specified bean class
   */
  public static Iterator getPropertyNames(Class clazz) {
    return getPropertyDescriptors(clazz).keySet().iterator();
  }

  /**
   * Get specified property descriptor
   */
  public static PropertyDescriptor getPropertyDescriptor(Class clazz, String property) {
    return (PropertyDescriptor)getPropertyDescriptors(clazz).get(property);
  }

  /**
   * Get specified property value
   */
  public static Object getProperty(Object bean, String property) throws NoSuchMethodException, IllegalAccessException, InvocationTargetException {
    PropertyDescriptor descriptor = getPropertyDescriptor(bean.getClass(), property);
    if (descriptor == null)
      throw new NoSuchMethodException("Cannot find property " + bean.getClass().getName() + "." + property);
    Method method = descriptor.getReadMethod();
    if (method == null)
      throw new NoSuchMethodException("Cannot find getter for " + bean.getClass().getName() + "." + property);
    return method.invoke(bean, null);
  }

  /**
   * Get specified nested property value
   */
  public static Object getNestedProperty(Object bean, String property) throws NoSuchMethodException, IllegalAccessException, InvocationTargetException {
    if (property.indexOf('.') > 0) {
      String[] path = property.split("\\.");
      for (int i = 0; i < path.length && bean != null; i++) {
        bean = getProperty(bean, path[i]);
      }
      return bean;
    } else {
      return getProperty(bean, property);
    }
  }

  /**
   * Set specified property value
   */
  public static void setProperty(Object bean, String property, Object value) throws NoSuchMethodException, IllegalAccessException, InvocationTargetException {
    PropertyDescriptor descriptor = getPropertyDescriptor(bean.getClass(), property);
    if (descriptor == null)
      throw new NoSuchMethodException("Cannot find property " + bean.getClass().getName() + "." + property);
    Method method = descriptor.getWriteMethod();
    if (method == null)
      throw new NoSuchMethodException("Cannot find setter for " + bean.getClass().getName() + "." + property);
    method.invoke(bean, new Object[]{ value });
  }

  /**
   * Set nested property given by property path, starting at specified
   * index. Dynamically create beans if necessary. Take care not to
   * leave the bean changed if an exception occurs.
   */
  private static void setNestedPropertyWithCreate(Object bean, String[] path, int start, Object value) throws NoSuchMethodException, IllegalAccessException, InvocationTargetException, InstantiationException {
    for (int i = start; i < path.length - 1; i++) {
      Object object = getProperty(bean, path[i]);
      if (object == null) {
        PropertyDescriptor descr =
          getPropertyDescriptor(bean.getClass(), path[i]);
        object = descr.getPropertyType().newInstance();
        setNestedPropertyWithCreate(object, path, i + 1, value);
        setProperty(bean, path[i], object);
        return;
      }
      bean = object;
    }
    setProperty(bean, path[path.length - 1], value);      
  }

  /**
   * Set specified nested property value
   */
  public static void setNestedProperty(Object bean, String property, Object value) throws NoSuchMethodException, IllegalAccessException, InvocationTargetException, InstantiationException {
    int lastDot = property.lastIndexOf('.');
    if (lastDot > 0) {
      setNestedPropertyWithCreate(bean, property.split("\\."), 0, value);
    } else {
      setProperty(bean, property, value);     
    }
  }


}