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/* $Id: AnnotationUtils.java 992060 2010-09-02 19:09:47Z simonetripodi $
 *
 * 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
 *
 *      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.apache.commons.digester.annotations.utils;

import java.lang.annotation.Annotation;

import org.apache.commons.beanutils.MethodUtils;

/**
 * Simple utility class to introspect annotations.
 *
 * @since 2.1
 */
public class AnnotationUtils {

    /**
     * The {@code value} string constant.
     */
    private static final String VALUE = "value";

    /**
     * The {@code pattern} string constant.
     */
    private static final String PATTERN = "pattern";

    /**
     * This class can't be instantiated.
     */
    private AnnotationUtils() {
        // this class can' be instantiated
    }

    /**
     * Extract the {@code value()} from annotation.
     *
     * @param annotation the annotation has to be introspected.
     * @return the annotation {@code value()}.
     */
    public static Object getAnnotationValue(Annotation annotation) {
        return invokeAnnotationMethod(annotation, VALUE);
    }

    /**
     * Extract the {@code pattern()} from annotation.
     *
     * @param annotation the annotation has to be introspected.
     * @return the annotation {@code pattern()}.
     */
    public static String getAnnotationPattern(Annotation annotation) {
        Object ret = invokeAnnotationMethod(annotation, PATTERN);
        if (ret != null) {
            return (String) ret;
        }
        return null;
    }

    /**
     * Extract the Annotations array {@code value()} from annotation if present,
     * nul otherwise.
     *
     * @param annotation the annotation has to be introspected.
     * @return the annotation {@code value()} as Annotations array.
     */
    public static Annotation[] getAnnotationsArrayValue(Annotation annotation) {
        Object value = getAnnotationValue(annotation);
        if (value != null
                && value.getClass().isArray()
                && Annotation.class.isAssignableFrom(value.getClass().getComponentType())) {
            return (Annotation[]) value;
        }
        return null;
    }

    /**
     * Invokes an annotation method.
     *
     * @param annotationn the annotation has to be introspected.
     * @param method the method name to execute.
     * @return the annotation method value, null if any error occurs.
     */
    private static Object invokeAnnotationMethod(Annotation annotation, String method) {
        try {
            return MethodUtils.invokeExactMethod(annotation, method, null);
        } catch (Throwable t) {
            return null;
        }
    }

}