001    package org.apache.ojb.broker.util;
002    
003    /* Copyright 2003-2005 The Apache Software Foundation
004     *
005     * Licensed under the Apache License, Version 2.0 (the "License");
006     * you may not use this file except in compliance with the License.
007     * You may obtain a copy of the License at
008     *
009     *     http://www.apache.org/licenses/LICENSE-2.0
010     *
011     * Unless required by applicable law or agreed to in writing, software
012     * distributed under the License is distributed on an "AS IS" BASIS,
013     * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
014     * See the License for the specific language governing permissions and
015     * limitations under the License.
016     */
017    
018    import java.lang.reflect.Constructor;
019    
020    import org.apache.ojb.broker.metadata.ClassNotPersistenceCapableException;
021    
022    /**
023     * This class helps us to construct new instances.
024     * We don't want to rely on public default constructors and
025     * have to try hard to also use private or protected constructors.
026     *
027     * @author Thomas Mahler
028     * @author Lance Eason
029     *
030     * @version $Id: ConstructorHelper.java,v 1.1 2007-08-24 22:17:36 ewestfal Exp $
031     */
032    public class ConstructorHelper
033    {
034        /**
035         * represents a zero sized parameter array
036         */
037        private static final Object[] NO_ARGS = {};
038    
039        /**
040         * no public constructor, please use the static method only.
041         */
042        private ConstructorHelper()
043        {
044        }
045    
046        /**
047         * create a new instance of class clazz.
048         * first use the public default constructor.
049         * If this fails also try to use protected an private constructors.
050         * @param clazz the class to instantiate
051         * @return the fresh instance of class clazz
052         * @throws InstantiationException
053         */
054        public static Object instantiate(Class clazz) throws InstantiationException
055        {
056            Object result = null;
057            try
058            {
059                result = ClassHelper.newInstance(clazz);
060            }
061            catch(IllegalAccessException e)
062            {
063                try
064                {
065                    result = ClassHelper.newInstance(clazz, true);
066                }
067                catch(Exception e1)
068                {
069                    throw new ClassNotPersistenceCapableException("Can't instantiate class '"
070                            + (clazz != null ? clazz.getName() : "null")
071                            + "', message was: " + e1.getMessage() + ")", e1);
072                }
073            }
074            return result;
075        }
076    
077        /**
078         * create a new instance of the class represented by the no-argument constructor provided
079         * @param constructor the zero argument constructor for the class
080         * @return a new instance of the class
081         * @throws InstantiationException
082         * @throws ClassNotPersistenceCapableException if the constructor is null or there is an
083         *   exception while trying to create a new instance
084         */
085        public static Object instantiate(Constructor constructor) throws InstantiationException
086        {
087            if(constructor == null)
088            {
089                throw new ClassNotPersistenceCapableException(
090                        "A zero argument constructor was not provided!");
091            }
092    
093            Object result = null;
094            try
095            {
096                result = constructor.newInstance(NO_ARGS);
097            }
098            catch(InstantiationException e)
099            {
100                throw e;
101            }
102            catch(Exception e)
103            {
104                throw new ClassNotPersistenceCapableException("Can't instantiate class '"
105                        + (constructor != null ? constructor.getDeclaringClass().getName() : "null")
106                        + "' with given constructor: " + e.getMessage(), e);
107            }
108            return result;
109        }
110    }