001 /*
002 * Licensed to the Apache Software Foundation (ASF) under one or more
003 * contributor license agreements. See the NOTICE file distributed with
004 * this work for additional information regarding copyright ownership.
005 * The ASF licenses this file to You under the Apache License, Version 2.0
006 * (the "License"); you may not use this file except in compliance with
007 * the License. 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 package org.apache.commons.collections.functors;
018
019 import java.io.Serializable;
020 import java.lang.reflect.Constructor;
021 import java.lang.reflect.InvocationTargetException;
022
023 import org.apache.commons.collections.FunctorException;
024 import org.apache.commons.collections.Transformer;
025
026 /**
027 * Transformer implementation that creates a new object instance by reflection.
028 *
029 * @since Commons Collections 3.0
030 * @version $Revision: 646777 $ $Date: 2008-04-10 13:33:15 +0100 (Thu, 10 Apr 2008) $
031 *
032 * @author Stephen Colebourne
033 */
034 public class InstantiateTransformer implements Transformer, Serializable {
035
036 /** The serial version */
037 private static final long serialVersionUID = 3786388740793356347L;
038
039 /** Singleton instance that uses the no arg constructor */
040 public static final Transformer NO_ARG_INSTANCE = new InstantiateTransformer();
041
042 /** The constructor parameter types */
043 private final Class[] iParamTypes;
044 /** The constructor arguments */
045 private final Object[] iArgs;
046
047 /**
048 * Transformer method that performs validation.
049 *
050 * @param paramTypes the constructor parameter types
051 * @param args the constructor arguments
052 * @return an instantiate transformer
053 */
054 public static Transformer getInstance(Class[] paramTypes, Object[] args) {
055 if (((paramTypes == null) && (args != null))
056 || ((paramTypes != null) && (args == null))
057 || ((paramTypes != null) && (args != null) && (paramTypes.length != args.length))) {
058 throw new IllegalArgumentException("Parameter types must match the arguments");
059 }
060
061 if (paramTypes == null || paramTypes.length == 0) {
062 return NO_ARG_INSTANCE;
063 } else {
064 paramTypes = (Class[]) paramTypes.clone();
065 args = (Object[]) args.clone();
066 }
067 return new InstantiateTransformer(paramTypes, args);
068 }
069
070 /**
071 * Constructor for no arg instance.
072 */
073 private InstantiateTransformer() {
074 super();
075 iParamTypes = null;
076 iArgs = null;
077 }
078
079 /**
080 * Constructor that performs no validation.
081 * Use <code>getInstance</code> if you want that.
082 *
083 * @param paramTypes the constructor parameter types, not cloned
084 * @param args the constructor arguments, not cloned
085 */
086 public InstantiateTransformer(Class[] paramTypes, Object[] args) {
087 super();
088 iParamTypes = paramTypes;
089 iArgs = args;
090 }
091
092 /**
093 * Transforms the input Class object to a result by instantiation.
094 *
095 * @param input the input object to transform
096 * @return the transformed result
097 */
098 public Object transform(Object input) {
099 try {
100 if (input instanceof Class == false) {
101 throw new FunctorException(
102 "InstantiateTransformer: Input object was not an instanceof Class, it was a "
103 + (input == null ? "null object" : input.getClass().getName()));
104 }
105 Constructor con = ((Class) input).getConstructor(iParamTypes);
106 return con.newInstance(iArgs);
107
108 } catch (NoSuchMethodException ex) {
109 throw new FunctorException("InstantiateTransformer: The constructor must exist and be public ");
110 } catch (InstantiationException ex) {
111 throw new FunctorException("InstantiateTransformer: InstantiationException", ex);
112 } catch (IllegalAccessException ex) {
113 throw new FunctorException("InstantiateTransformer: Constructor must be public", ex);
114 } catch (InvocationTargetException ex) {
115 throw new FunctorException("InstantiateTransformer: Constructor threw an exception", ex);
116 }
117 }
118
119 }