001/**
002 * Copyright (c) 2011, The University of Southampton and the individual contributors.
003 * All rights reserved.
004 *
005 * Redistribution and use in source and binary forms, with or without modification,
006 * are permitted provided that the following conditions are met:
007 *
008 *   *  Redistributions of source code must retain the above copyright notice,
009 *      this list of conditions and the following disclaimer.
010 *
011 *   *  Redistributions in binary form must reproduce the above copyright notice,
012 *      this list of conditions and the following disclaimer in the documentation
013 *      and/or other materials provided with the distribution.
014 *
015 *   *  Neither the name of the University of Southampton nor the names of its
016 *      contributors may be used to endorse or promote products derived from this
017 *      software without specific prior written permission.
018 *
019 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND
020 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
021 * WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
022 * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR
023 * ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
024 * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
025 * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON
026 * ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
027 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
028 * SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
029 */
030package org.openimaj.util.reflection;
031
032import java.lang.reflect.Array;
033import java.lang.reflect.GenericArrayType;
034import java.lang.reflect.Method;
035import java.lang.reflect.Modifier;
036import java.lang.reflect.ParameterizedType;
037import java.lang.reflect.Type;
038import java.lang.reflect.TypeVariable;
039import java.util.ArrayList;
040import java.util.HashMap;
041import java.util.List;
042import java.util.Map;
043
044/**
045 * Utility methods for java reflection
046 * 
047 * @author Jonathon Hare (jsh2@ecs.soton.ac.uk)
048 *
049 */
050public class ReflectionUtils {
051        /**
052         * Test if a class has a "public static main(String [] args)" method 
053         * @param clz the class
054         * @return true if main method exists; false otherwise
055         */
056        public static boolean hasMain(Class<?> clz) {
057                return getMain(clz) != null;
058        }
059        
060        /**
061         * Get the "public static main(String [] args)" method of the class,
062         * or null if it doesn't have one.
063         * 
064         * @param clz the class
065         * @return the main method, or null if it doesn't exist
066         */
067        public static Method getMain(Class<?> clz) {
068                try {
069                        Method m =  clz.getMethod("main", String[].class);
070                        
071                        if (Modifier.isPublic(m.getModifiers()) && 
072                                Modifier.isStatic(m.getModifiers()))
073                                return m;
074                } catch (NoSuchMethodException e1) {
075                        //do nothing
076                }
077                return null;
078        }
079        
080        /**
081         * Get the underlying class for a type, or null if the type is a variable
082         * type.
083         * 
084         * @param type
085         *            the type
086         * @return the underlying class
087         */
088        public static Class<?> getClass(Type type) {
089                if (type instanceof Class) {
090                        return (Class<?>) type;
091                } else if (type instanceof ParameterizedType) {
092                        return getClass(((ParameterizedType) type).getRawType());
093                } else if (type instanceof GenericArrayType) {
094                        Type componentType = ((GenericArrayType) type)
095                                        .getGenericComponentType();
096                        Class<?> componentClass = getClass(componentType);
097                        if (componentClass != null) {
098                                return Array.newInstance(componentClass, 0).getClass();
099                        } else {
100                                return null;
101                        }
102                } else {
103                        return null;
104                }
105        }
106
107        /**
108         * Get the actual type arguments a child class has used to extend a generic
109         * base class. An implementation kindly described in this blog post: http://www.artima.com/weblogs/viewpost.jsp?thread=208860
110         * by
111         * @param <T> The type of the base class
112         * 
113         * @param baseClass
114         *            the base class
115         * @param childClass
116         *            the child class
117         * @return a list of the raw classes for the actual type arguments.
118         */
119        public static <T> List<Class<?>> getTypeArguments(Class<T> baseClass, Class<? extends T> childClass) {
120                Map<Type, Type> resolvedTypes = new HashMap<Type, Type>();
121                Type type = childClass;
122                // start walking up the inheritance hierarchy until we hit baseClass
123                while (!getClass(type).equals(baseClass)) {
124                        if (type instanceof Class) {
125                                // there is no useful information for us in raw types, so just
126                                // keep going.
127                                type = ((Class<?>) type).getGenericSuperclass();
128                        } else {
129                                ParameterizedType parameterizedType = (ParameterizedType) type;
130                                Class<?> rawType = (Class<?>) parameterizedType.getRawType();
131
132                                Type[] actualTypeArguments = parameterizedType.getActualTypeArguments();
133                                TypeVariable<?>[] typeParameters = rawType.getTypeParameters();
134                                for (int i = 0; i < actualTypeArguments.length; i++) {
135                                        resolvedTypes.put(typeParameters[i], actualTypeArguments[i]);
136                                }
137
138                                if (!rawType.equals(baseClass)) {
139                                        type = rawType.getGenericSuperclass();
140                                }
141                        }
142                }
143
144                // finally, for each actual type argument provided to baseClass,
145                // determine (if possible)
146                // the raw class for that type argument.
147                Type[] actualTypeArguments;
148                if (type instanceof Class) {
149                        actualTypeArguments = ((Class<?>) type).getTypeParameters();
150                } else {
151                        actualTypeArguments = ((ParameterizedType) type).getActualTypeArguments();
152                }
153                List<Class<?>> typeArgumentsAsClasses = new ArrayList<Class<?>>();
154                // resolve types by chasing down type variables.
155                for (Type baseType : actualTypeArguments) {
156                        while (resolvedTypes.containsKey(baseType)) {
157                                baseType = resolvedTypes.get(baseType);
158                        }
159                        typeArgumentsAsClasses.add(getClass(baseType));
160                }
161                return typeArgumentsAsClasses;
162        }
163}