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Apache Commons BeanUtils provides an easy-to-use but flexible wrapper around reflection and introspection.
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/*
 * 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
 *
 *      https://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.commons.beanutils2;

import java.beans.PropertyDescriptor;
import java.lang.ref.Reference;
import java.lang.ref.SoftReference;
import java.util.HashMap;
import java.util.Map;
import java.util.Objects;
import java.util.WeakHashMap;

/**
 * Implements {@link DynaClass} to wrap standard JavaBean instances.
 * 
 * This class should not usually need to be used directly to create new {@link WrapDynaBean} instances - it's usually better to call the {@link WrapDynaBean}
 * constructor. For example:
 * 
 *
 *  *   Object javaBean = ...;
 *   DynaBean wrapper = new WrapDynaBean(javaBean);
 * 
 */
public class WrapDynaClass implements DynaClass {

    /**
     * A class representing the combined key for the cache of {@code WrapDynaClass} instances. A single key consists of a bean class and an instance of
     * {@code PropertyUtilsBean}. Instances are immutable.
     */
    private static final class CacheKey {

        /** The bean class. */
        private final Class beanClass;

        /** The instance of PropertyUtilsBean. */
        private final PropertyUtilsBean propUtils;

        /**
         * Creates a new instance of {@code CacheKey}.
         *
         * @param beanCls the bean class
         * @param pu      the instance of {@code PropertyUtilsBean}
         */
        public CacheKey(final Class beanCls, final PropertyUtilsBean pu) {
            beanClass = beanCls;
            propUtils = pu;
        }

        @Override
        public boolean equals(final Object obj) {
            if (this == obj) {
                return true;
            }
            if (!(obj instanceof CacheKey)) {
                return false;
            }

            final CacheKey c = (CacheKey) obj;
            return beanClass.equals(c.beanClass) && propUtils.equals(c.propUtils);
        }

        @Override
        public int hashCode() {
            final int factor = 31;
            int result = 17;
            result = factor * beanClass.hashCode() + result;
            result = factor * propUtils.hashCode() + result;
            return result;
        }
    }

    private static final ContextClassLoaderLocal> CLASSLOADER_CACHE = new ContextClassLoaderLocal>() {
        @Override
        protected Map initialValue() {
            return new WeakHashMap<>();
        }
    };

    /**
     * Clear our cache of WrapDynaClass instances.
     */
    public static void clear() {
        getClassesCache().clear();
    }

    /**
     * Create (if necessary) and return a new {@code WrapDynaClass} instance for the specified bean class.
     *
     * @param beanClass Bean class for which a WrapDynaClass is requested
     * @return A new Wrap {@link DynaClass}
     */
    public static WrapDynaClass createDynaClass(final Class beanClass) {
        return createDynaClass(beanClass, null);
    }

    /**
     * Create (if necessary) and return a new {@code WrapDynaClass} instance for the specified bean class using the given {@code PropertyUtilsBean} instance for
     * introspection. Using this method a specially configured {@code PropertyUtilsBean} instance can be hooked into the introspection mechanism of the managed
     * bean. The argument is optional; if no {@code PropertyUtilsBean} object is provided, the default instance is used.
     *
     * @param beanClass Bean class for which a WrapDynaClass is requested
     * @param pu        the optional {@code PropertyUtilsBean} to be used for introspection
     * @return A new Wrap {@link DynaClass}
     * @since 1.9
     */
    public static WrapDynaClass createDynaClass(final Class beanClass, final PropertyUtilsBean pu) {
        final PropertyUtilsBean propUtils = pu != null ? pu : PropertyUtilsBean.getInstance();
        final CacheKey key = new CacheKey(beanClass, propUtils);
        return getClassesCache().computeIfAbsent(key, k -> new WrapDynaClass(beanClass, propUtils));
    }

    /**
     * Returns the cache for the already created class instances. For each combination of bean class and {@code PropertyUtilsBean} instance an entry is created
     * in the cache.
     *
     * @return the cache for already created {@code WrapDynaClass} instances
     */
    private static Map getClassesCache() {
        return CLASSLOADER_CACHE.get();
    }

    /**
     * Name of the JavaBean class represented by this WrapDynaClass.
     */
    private final String beanClassName;

    /**
     * Reference to the JavaBean class represented by this WrapDynaClass.
     */
    private final Reference> beanClassRef;

    /** Stores the associated {@code PropertyUtilsBean} instance. */
    private final PropertyUtilsBean propertyUtilsBean;

    /**
     * The set of PropertyDescriptors for this bean class, keyed by the property name. Individual descriptor instances will be the same instances as those in
     * the {@code descriptors} list.
     */
    protected HashMap descriptorsMap = new HashMap<>();

    /**
     * The set of dynamic properties that are part of this DynaClass.
     */
    protected DynaProperty[] properties;

    /**
     * The set of dynamic properties that are part of this DynaClass, keyed by the property name. Individual descriptor instances will be the same instances as
     * those in the {@code properties} list.
     */
    protected HashMap propertiesMap = new HashMap<>();

    /**
     * Constructs a new WrapDynaClass for the specified JavaBean class. This constructor is private; WrapDynaClass instances will be created as needed via calls
     * to the {@code createDynaClass(Class)} method.
     *
     * @param beanClass JavaBean class to be introspected around
     * @param propUtils the {@code PropertyUtilsBean} associated with this class
     */
    private WrapDynaClass(final Class beanClass, final PropertyUtilsBean propUtils) {
        this.beanClassRef = new SoftReference<>(beanClass);
        this.beanClassName = beanClass.getName();
        this.propertyUtilsBean = propUtils;
        introspect();
    }

    /**
     * Gets the class of the underlying wrapped bean.
     *
     * @return the class of the underlying wrapped bean
     * @since 1.8.0
     */
    protected Class getBeanClass() {
        return beanClassRef.get();
    }

    /**
     * 
     * Return an array of {@code PropertyDescriptor} for the properties currently defined in this DynaClass. If no properties are defined, a zero-length array
     * will be returned.
     * 
     *
     * 
     * FIXME - Should we really be implementing {@code getBeanInfo()} instead, which returns property descriptors and a bunch of other stuff?
     * 
     *
     * @return the set of properties for this DynaClass
     */
    @Override
    public DynaProperty[] getDynaProperties() {
        return properties.clone();
    }

    /**
     * Gets a property descriptor for the specified property, if it exists; otherwise, return {@code null}.
     *
     * @param name Name of the dynamic property for which a descriptor is requested
     * @return The descriptor for the specified property
     * @throws IllegalArgumentException if no property name is specified
     */
    @Override
    public DynaProperty getDynaProperty(final String name) {
        return propertiesMap.get(Objects.requireNonNull(name, "name"));
    }

    /**
     * Gets the name of this DynaClass (analogous to the {@code getName()} method of {@link Class}, which allows the same {@code DynaClass} implementation class
     * to support different dynamic classes, with different sets of properties.
     *
     * @return the name of the DynaClass
     */
    @Override
    public String getName() {
        return beanClassName;
    }

    /**
     * Gets the PropertyDescriptor for the specified property name, if any; otherwise return {@code null}.
     *
     * @param name Name of the property to be retrieved
     * @return The descriptor for the specified property
     */
    public PropertyDescriptor getPropertyDescriptor(final String name) {
        return descriptorsMap.get(name);
    }

    /**
     * Returns the {@code PropertyUtilsBean} instance associated with this class. This bean is used for introspection.
     *
     * @return the associated {@code PropertyUtilsBean} instance
     * @since 1.9
     */
    protected PropertyUtilsBean getPropertyUtilsBean() {
        return propertyUtilsBean;
    }

    /**
     * Introspect our bean class to identify the supported properties.
     */
    protected void introspect() {
        // Look up the property descriptors for this bean class
        final Class beanClass = getBeanClass();
        PropertyDescriptor[] regulars = getPropertyUtilsBean().getPropertyDescriptors(beanClass);
        if (regulars == null) {
            regulars = PropertyDescriptors.EMPTY_ARRAY;
        }
        Map mappeds = PropertyUtils.getMappedPropertyDescriptors(beanClass);
        if (mappeds == null) {
            mappeds = new HashMap<>();
        }

        // Construct corresponding DynaProperty information
        properties = new DynaProperty[regulars.length + mappeds.size()];
        for (int i = 0; i < regulars.length; i++) {
            descriptorsMap.put(regulars[i].getName(), regulars[i]);
            properties[i] = new DynaProperty(regulars[i].getName(), regulars[i].getPropertyType());
            propertiesMap.put(properties[i].getName(), properties[i]);
        }

        int j = regulars.length;

        for (final Object value : mappeds.values()) {
            final PropertyDescriptor descriptor = (PropertyDescriptor) value;
            properties[j] = new DynaProperty(descriptor.getName(), Map.class);
            propertiesMap.put(properties[j].getName(), properties[j]);
            j++;
        }
    }

    /**
     * 
     * Instantiates a new standard JavaBean instance associated with this DynaClass and return it wrapped in a new WrapDynaBean instance. NOTE
     * the JavaBean should have a no argument constructor.
     * 
     *
     * 
     * NOTE - Most common use cases should not need to use this method. It is usually better to create new {@code WrapDynaBean} instances by
     * calling its constructor. For example:
     * 
     *
     * {@code
     *   Object javaBean = ...;
     *   DynaBean wrapper = new WrapDynaBean(javaBean);
     * }
     * 
     * (This method is needed for some kinds of {@code DynaBean} framework.)
     * 
     *
     * @return A new {@code DynaBean} instance
     * @throws IllegalAccessException if the Class or the appropriate constructor is not accessible
     * @throws InstantiationException if this Class represents an abstract class, an array class, a primitive type, or void; or if instantiation fails for some
     *                                other reason
     */
    @Override
    public DynaBean newInstance() throws IllegalAccessException, InstantiationException {
        return new WrapDynaBean(getBeanClass().newInstance());
    }
}