org.joda.beans.MetaBeans Maven / Gradle / Ivy

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/*
 *  Copyright 2001-present Stephen Colebourne
 *
 *  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.
 */
package org.joda.beans;

import java.lang.reflect.InvocationTargetException;
import java.util.concurrent.ConcurrentHashMap;

import org.joda.beans.impl.flexi.FlexiBean;
import org.joda.beans.impl.map.MapBean;

/**
 * Utilities for registered meta-beans.
 */
final class MetaBeans {

    /**
     * The cache of meta-beans.
     */
    private static final ConcurrentHashMap, MetaBean> META_BEANS = new ConcurrentHashMap<>();

    /**
     * Restricted constructor.
     */
    private MetaBeans() {
    }

    //-----------------------------------------------------------------------
    /**
     * Gets the meta-bean for a class.
     * 
     * This only works for those beans that have registered their meta-beans.
     * 

     * A {@code Class} may use a static initializer block to call {@code register}.
     * The edge case where the class is loaded but not initialized is handled
     * by forcing the class to be initialized if necessary.
     * 
     * @param cls  the class to get the meta-bean for, not null
     * @return the meta-bean, not null
     * @throws IllegalArgumentException if unable to obtain the meta-bean
     */
    static MetaBean lookup(Class cls) {
        MetaBean meta = META_BEANS.get(cls);
        if (meta == null) {
            return metaBeanLookup(cls);
        }
        return meta;
    }

    // lookup the MetaBean outside the fast path, aiding hotspot inlining
    private static MetaBean metaBeanLookup(Class cls) {
        // handle dynamic beans
        if (cls == FlexiBean.class) {
            return new FlexiBean().metaBean();
        } else if (cls == MapBean.class) {
            return new MapBean().metaBean();
        } else if (DynamicBean.class.isAssignableFrom(cls)) {
            try {
                return cls.asSubclass(DynamicBean.class).getDeclaredConstructor().newInstance().metaBean();
            } catch (NoSuchMethodException | InvocationTargetException | InstantiationException | IllegalAccessException ex) {
                throw new IllegalArgumentException("Unable to find meta-bean for a DynamicBean: " + cls.getName(), ex);
            }
        }
        // a Class can be loaded without being initialized
        // in this state, the static initializers have not run, and thus the metabean not registered
        // here initialization is forced to handle that scenario
        try {
            cls = Class.forName(cls.getName(), true, cls.getClassLoader());
        } catch (ClassNotFoundException | Error ex) {
            // should be impossible
            throw new IllegalArgumentException("Unable to find meta-bean: " + cls.getName(), ex);
        }
        MetaBean meta = META_BEANS.get(cls);
        if (meta == null) {
            throw new IllegalArgumentException("Unable to find meta-bean: " + cls.getName());
        }
        return meta;
    }

    /**
     * Registers a meta-bean.
     * 
     * This should be done for all beans in a static factory where possible.
     * If the meta-bean is dynamic, this method should not be called.
     * 
     * @param metaBean  the meta-bean, not null
     * @throws IllegalArgumentException if unable to register
     */
    static void register(MetaBean metaBean) {
        Class type = metaBean.beanType();
        if (META_BEANS.putIfAbsent(type, metaBean) != null) {
            throw new IllegalArgumentException("Cannot register class twice: " + type.getName());
        }
    }

}