001/*
002 *  Licensed to the Apache Software Foundation (ASF) under one
003 *  or more contributor license agreements.  See the NOTICE file
004 *  distributed with this work for additional information
005 *  regarding copyright ownership.  The ASF licenses this file
006 *  to you under the Apache License, Version 2.0 (the
007 *  "License"); you may not use this file except in compliance
008 *  with the License.  You may obtain a copy of the License at
009 *
010 *    http://www.apache.org/licenses/LICENSE-2.0
011 *
012 *  Unless required by applicable law or agreed to in writing,
013 *  software distributed under the License is distributed on an
014 *  "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
015 *  KIND, either express or implied.  See the License for the
016 *  specific language governing permissions and limitations
017 *  under the License.
018 *
019 */
020package org.apache.directory.server.core.annotations;
021
022
023import java.lang.annotation.Annotation;
024import java.lang.reflect.Method;
025
026
027/**
028 * An helper class used to find annotations in methods and classes
029 *
030 * @author <a href="mailto:dev@directory.apache.org">Apache Directory Project</a>
031 */
032public final class AnnotationUtils
033{
034    private AnnotationUtils()
035    {
036    }
037
038
039    /**
040     * Get an instance of a class extracted from the annotation found in the method
041     * or the class. We iterate on the stack trace until we find the desired annotation.
042     * 
043     * @param clazz The Annotation we want to get an instance for
044     * @return The instance or null if no annotation is found
045     * @throws ClassNotFoundException If we can't find a class
046     */
047    public static Object getInstance( Class<? extends Annotation> clazz ) throws ClassNotFoundException
048    {
049        Object instance = null;
050
051        // Get the caller by inspecting the stackTrace
052        StackTraceElement[] stackTrace = Thread.currentThread().getStackTrace();
053
054        // Iterate on the stack trace.
055        for ( int i = stackTrace.length - 1; i >= 0; i-- )
056        {
057            Class<?> classCaller = null;
058
059            // Get the current class
060            try
061            {
062                classCaller = Class.forName( stackTrace[i].getClassName() );
063            }
064            catch ( ClassNotFoundException cnfe )
065            {
066                // Corner case : we just have to go higher in the stack in this case.
067                continue;
068            }
069
070            // Get the current method
071            String methodCaller = stackTrace[i].getMethodName();
072
073            // Check if we have any annotation associated with the method
074            Method[] methods = classCaller.getMethods();
075
076            for ( Method method : methods )
077            {
078                if ( methodCaller.equals( method.getName() ) )
079                {
080                    instance = method.getAnnotation( clazz );
081
082                    if ( instance != null )
083                    {
084                        break;
085                    }
086                }
087            }
088
089            if ( instance == null )
090            {
091                instance = classCaller.getAnnotation( clazz );
092            }
093
094            if ( instance != null )
095            {
096                break;
097            }
098        }
099
100        return instance;
101    }
102}