home | career | drupal | java | mac | mysql | perl | scala | uml | unix

Groovy example source code file (MetaClassRegistry.java)

This example Groovy source code file (MetaClassRegistry.java) is included in the DevDaily.com "Java Source Code Warehouse" project. The intent of this project is to help you "Learn Java by Example" TM.

Java - Groovy tags/keywords

classnotfoundexception, closuremetaclass, constructor, constructor, groovyruntimeexception, iterator, metaclass, metaclass, metaclasscreationhandle, metaclasscreationhandle, metaclassimpl, metaclassregistry, metaclassregistry, reason, reflection, util

The Groovy MetaClassRegistry.java source code

/*
 * Copyright 2003-2007 the original author or authors.
 *
 * 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 groovy.lang;

import org.codehaus.groovy.runtime.GeneratedClosure;
import org.codehaus.groovy.runtime.metaclass.ClosureMetaClass;

import java.lang.reflect.Constructor;
import java.util.Iterator;

/**
 * A MetaClassRegistry is an object that is responsible for managing the a cache of MetaClass instances. Each
 * java.lang.Class instance has an associated MetaClass and client code can query this interface for the MetaClass for
 * a given associated java.lang.Class
 *
 * @see groovy.lang.MetaClass
 *
 * @author John Wilson
 * @author Graeme Rocher
 * @author <a href="mailto:blackdrag@gmx.org">Jochen Theodorou
 *
 */
public interface MetaClassRegistry {
    /*
     * The main function of the registry
     * If a meta class exists then return it
     * otherwise create one, put it in the registry and return it
     */
    MetaClass getMetaClass(Class theClass);
    
    /*
     * Do we really want these two?
     */
    void setMetaClass(Class theClass, MetaClass theMetaClass);

    /**
     * Removes a cached MetaClass from the registry
     * @param theClass The Java class of the MetaClass to remove
     */
    void removeMetaClass(Class theClass);

    /**
     * Retrieves the MetaClassCreationHandle that is responsible for constructing MetaClass instances
     *
     * @return The MetaClassCreationHandle instance
     */
    MetaClassCreationHandle getMetaClassCreationHandler();

    /**
     * Sets the MetaClassCreationHandle instance that is responsible for constructing instances
     *
     * @param handle The handle instance
     */
    void setMetaClassCreationHandle(MetaClassCreationHandle handle);

    /**
     * adds a ConstantMetaClassChangeListener
     *
     * @param listener - the update listener
     */
    void addMetaClassRegistryChangeEventListener(MetaClassRegistryChangeEventListener listener);

    /**
     * removes a ConstantMetaClassChangeListener
     *
     * @param listener - the update listener
     */
    void removeMetaClassRegistryChangeEventListener(MetaClassRegistryChangeEventListener listener);

    /**
     * Returns all registered ConstantMetaClassChangeListener objects.
     *
     * @return an array containing all change listener
     */
    MetaClassRegistryChangeEventListener[] getMetaClassRegistryChangeEventListeners();

    /**
     * gets a snapshot of the current constant meta classes and returns it as Iterator.
     * Modifications done using this Iterator will not cause a ConcurrentModificationException.
     * If a MetaClass is removed using this Iterator, then the MetaClass will only
     * be removed if the MetaClass was not replaced by another MetaClass in the meantime.
     * If a MetaClass is added while using this Iterator, then it will be part of the Iteration.
     * If a MetaClass replaces another constant meta class, then the Iteration might show two
     * meta classes for the same class.<br/>
     * This Iterator may not used in multiple threads.
     *
     * @return Iterator for the constant meta classes
     */
    Iterator iterator();    
    
    /**
     * Class used as base for the creation of MetaClass implementations.
     * The Class defaults to MetaClassImpl, if the class loading fails to
     * find a special meta class. The name for such a meta class would be
     * the class name it is created for with the prefix
     * "groovy.runtime.metaclass." By replacing the handle in the registry
     * you can have any control over the creation of what MetaClass is used
     * for a class that you want to have. 
     * WARNING: experimental code, likely to change soon
     * @author Jochen Theodorou
     */
    class MetaClassCreationHandle {
        private boolean disableCustomMetaClassLookup;

        public final MetaClass create(Class theClass, MetaClassRegistry registry) {
           if (disableCustomMetaClassLookup)
               return createNormalMetaClass(theClass, registry);

            return createWithCustomLookup(theClass, registry);
        }

        private MetaClass createWithCustomLookup(Class theClass, MetaClassRegistry registry) {
            try {
                final Class customMetaClass = Class.forName("groovy.runtime.metaclass." + theClass.getName() + "MetaClass");
                if (DelegatingMetaClass.class.isAssignableFrom(customMetaClass)) {
                    final Constructor customMetaClassConstructor = customMetaClass.getConstructor(MetaClass.class);
                    MetaClass normalMetaClass = createNormalMetaClass(theClass, registry);
                    return (MetaClass)customMetaClassConstructor.newInstance(normalMetaClass);
                }
                else {
                    final Constructor customMetaClassConstructor = customMetaClass.getConstructor(MetaClassRegistry.class, Class.class);
                    return (MetaClass)customMetaClassConstructor.newInstance(registry, theClass);
                }
            }
            catch (final ClassNotFoundException e) {
                return createNormalMetaClass(theClass, registry);
            } catch (final Exception e) {
                throw new GroovyRuntimeException("Could not instantiate custom Metaclass for class: " + theClass.getName() + ". Reason: " + e, e);
            }
        }

        protected MetaClass createNormalMetaClass(Class theClass,MetaClassRegistry registry) {
            if (GeneratedClosure.class.isAssignableFrom(theClass)) {
                return new ClosureMetaClass(registry,theClass);
            } else {
                return new MetaClassImpl(registry, theClass);
            }
        }

        public boolean isDisableCustomMetaClassLookup() {
            return disableCustomMetaClassLookup;
        }

        /**
         * Set flag saying to disable lookup of custom meta classes
         * It's enough to call this method only once in your application for handle which was set in to registry
         * as every new handle will inherit this property
         * @param disableCustomMetaClassLookup flag saying to disable lookup of custom meta classes
         */
        public void setDisableCustomMetaClassLookup(boolean disableCustomMetaClassLookup) {
            this.disableCustomMetaClassLookup = disableCustomMetaClassLookup;
        }
    }
 }

Other Groovy examples (source code examples)

Here is a short list of links related to this Groovy MetaClassRegistry.java source code file:

new blog posts

 

Copyright 1998-2014 Alvin Alexander, alvinalexander.com
All Rights Reserved.