AnnotationInstanceProvider.java

/*
 * JBoss, Home of Professional Open Source
 * Copyright 2011, Red Hat, Inc. and/or its affiliates, and individual
 * contributors by the @authors tag. See the copyright.txt in the
 * distribution for a full listing of individual contributors.
 *
 * 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.jboss.solder.reflection;

import java.io.Serializable;
import java.lang.annotation.Annotation;
import java.lang.reflect.InvocationHandler;
import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Proxy;
import java.util.Map;
import java.util.concurrent.ConcurrentHashMap;
import java.util.concurrent.ConcurrentMap;

import javax.enterprise.util.AnnotationLiteral;

/**
 * <p>
 * Provides dynamic annotation creation. If you know the type of the annotation
 * instance to create at development time you should use
 * {@link AnnotationLiteral} instead of {@link AnnotationInstanceProvider}.
 * </p>
 * <p/>
 * <p>
 * {@link AnnotationInstanceProvider} creates a proxy, and will return values as
 * provided when the annotation instance was created. An
 * {@link AnnotationInstanceProvider} will cache generated proxy classes.
 * </p>
 *
 * @author Stuart Douglas
 * @author Pete Muir
 * @see AnnotationLiteral
 */
public class AnnotationInstanceProvider {

    private final ConcurrentMap<Class<?>, Class<?>> cache;

    public AnnotationInstanceProvider() {
        cache = new ConcurrentHashMap<Class<?>, Class<?>>();
    }

    /**
     * <p>
     * Returns an instance of the given annotation type with attribute values
     * specified in the map.
     * </p>
     * <p/>
     * <ul>
     * <li>
     * For {@link Annotation}, array and enum types the values must exactly match
     * the declared return type of the attribute or a {@link ClassCastException}
     * will result.</li>
     * <p/>
     * <li>
     * For character types the the value must be an instance of {@link Character}
     * or {@link String}.</li>
     * <p/>
     * <li>
     * Numeric types do not have to match exactly, as they are converted using
     * {@link Number}.</li>
     * </ul>
     * <p/>
     * <p>
     * If am member does not have a corresponding entry in the value map then the
     * annotations default value will be used.
     * </p>
     * <p/>
     * <p>
     * If the annotation member does not have a default value then a
     * NullMemberException will be thrown
     * </p>
     *
     * @param annotationType the type of the annotation instance to generate
     * @param values         the attribute values of this annotation
     */
    public <T extends Annotation> T get(Class<T> annotationType, Map<String, ?> values) {
        if (annotationType == null) {
            throw new IllegalArgumentException("Must specify an annotation");
        }
        Class<?> clazz = cache.get(annotationType);
        // Not safe against data race, but doesn't matter, we can recompute and
        // get the same value
        if (clazz == null) {
            // create the proxy class
            clazz = Proxy.getProxyClass(annotationType.getClassLoader(), annotationType, Serializable.class);
            cache.put(annotationType, clazz);
        }
        AnnotationInvocationHandler handler = new AnnotationInvocationHandler(values, annotationType);
        // create a new instance by obtaining the constructor via relection
        try {
            return annotationType.cast(clazz.getConstructor(new Class[]{InvocationHandler.class}).newInstance(new Object[]{handler}));
        } catch (IllegalArgumentException e) {
            throw new IllegalStateException("Error instantiating proxy for annotation. Annotation type: " + annotationType, e);
        } catch (InstantiationException e) {
            throw new IllegalStateException("Error instantiating proxy for annotation. Annotation type: " + annotationType, e);
        } catch (IllegalAccessException e) {
            throw new IllegalStateException("Error instantiating proxy for annotation. Annotation type: " + annotationType, e);
        } catch (InvocationTargetException e) {
            throw new IllegalStateException("Error instantiating proxy for annotation. Annotation type: " + annotationType, e.getCause());
        } catch (SecurityException e) {
            throw new IllegalStateException("Error accessing proxy constructor for annotation. Annotation type: " + annotationType, e);
        } catch (NoSuchMethodException e) {
            throw new IllegalStateException("Error accessing proxy constructor for annotation. Annotation type: " + annotationType, e);
        }
    }
}