    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
    018package org.apache.commons.beanutils2;
    019
    020import java.lang.reflect.Array;
    021import java.lang.reflect.Constructor;
    022import java.lang.reflect.InvocationTargetException;
    023import java.lang.reflect.Modifier;
    024
    025/**
    026 * <p>
    027 * Utility reflection methods focused on constructors, modeled after {@link MethodUtils}.
    028 * </p>
    029 *
    030 * <h2>Known Limitations</h2>
    031 * <h3>Accessing Public Constructors In A Default Access Superclass</h3>
    032 * <p>
    033 * There is an issue when invoking public constructors contained in a default access superclass. Reflection locates these constructors fine and correctly
    034 * assigns them as public. However, an {@code IllegalAccessException} is thrown if the constructors is invoked.
    035 * </p>
    036 *
    037 * <p>
    038 * {@code ConstructorUtils} contains a workaround for this situation. It will attempt to call {@code setAccessible} on this constructor. If this call succeeds,
    039 * then the method can be invoked as normal. This call will only succeed when the application has sufficient security privileges. If this call fails then a
    040 * warning will be logged and the method may fail.
    041 * </p>
    042 */
    043public class ConstructorUtils {
    044
    045    /**
    046     * Returns a constructor with single argument.
    047     *
    048     * @param <T>           the type of the constructor
    049     * @param klass         the class to be constructed
    050     * @param parameterType The constructor parameter type
    051     * @return null if matching accessible constructor cannot be found.
    052     * @see Class#getConstructor
    053     * @see #getAccessibleConstructor(java.lang.reflect.Constructor)
    054     */
    055    public static <T> Constructor<T> getAccessibleConstructor(final Class<T> klass, final Class<?> parameterType) {
    056
    057        final Class<?>[] parameterTypes = { parameterType };
    058        return getAccessibleConstructor(klass, parameterTypes);
    059    }
    060
    061    /**
    062     * Returns a constructor given a class and signature.
    063     *
    064     * @param <T>            the type to be constructed
    065     * @param klass          the class to be constructed
    066     * @param parameterTypes the parameter array
    067     * @return null if matching accessible constructor cannot be found
    068     * @see Class#getConstructor
    069     * @see #getAccessibleConstructor(java.lang.reflect.Constructor)
    070     */
    071    public static <T> Constructor<T> getAccessibleConstructor(final Class<T> klass, final Class<?>[] parameterTypes) {
    072
    073        try {
    074            return getAccessibleConstructor(klass.getConstructor(parameterTypes));
    075        } catch (final NoSuchMethodException e) {
    076            return null;
    077        }
    078    }
    079
    080    /**
    081     * Returns accessible version of the given constructor.
    082     *
    083     * @param <T>  the type of the constructor
    084     * @param ctor prototype constructor object.
    085     * @return {@code null} if accessible constructor cannot be found.
    086     * @see SecurityManager
    087     */
    088    public static <T> Constructor<T> getAccessibleConstructor(final Constructor<T> ctor) {
    089
    090        // Make sure we have a method to check
    091        if (ctor == null) {
    092            return null;
    093        }
    094
    095        // If the requested method is not public we cannot call it
    096        if (!Modifier.isPublic(ctor.getModifiers())) {
    097            return null;
    098        }
    099
    100        // If the declaring class is public, we are done
    101        final Class<T> clazz = ctor.getDeclaringClass();
    102        if (Modifier.isPublic(clazz.getModifiers())) {
    103            return ctor;
    104        }
    105
    106        // what else can we do?
    107        return null;
    108    }
    109
    110    /**
    111     * <p>
    112     * Find an accessible constructor with compatible parameters. Compatible parameters mean that every method parameter is assignable from the given
    113     * parameters. In other words, it finds constructor that will take the parameters given.
    114     * </p>
    115     *
    116     * <p>
    117     * First it checks if there is constructor matching the exact signature. If no such, all the constructors of the class are tested if their signatures are
    118     * assignment compatible with the parameter types. The first matching constructor is returned.
    119     * </p>
    120     *
    121     * @param <T>            the type of the class to be inspected
    122     * @param clazz          find constructor for this class
    123     * @param parameterTypes find method with compatible parameters
    124     * @return a valid Constructor object. If there's no matching constructor, returns {@code null}.
    125     */
    126    private static <T> Constructor<T> getMatchingAccessibleConstructor(final Class<T> clazz, final Class<?>[] parameterTypes) {
    127        // see if we can find the method directly
    128        // most of the time this works and it's much faster
    129        try {
    130            final Constructor<T> ctor = clazz.getConstructor(parameterTypes);
    131            try {
    132                //
    133                // XXX Default access superclass workaround
    134                //
    135                // When a public class has a default access superclass
    136                // with public methods, these methods are accessible.
    137                // Calling them from compiled code works fine.
    138                //
    139                // Unfortunately, using reflection to invoke these methods
    140                // seems to (wrongly) to prevent access even when the method
    141                // modifier is public.
    142                //
    143                // The following workaround solves the problem but will only
    144                // work from sufficiently privileges code.
    145                //
    146                // Better workarounds would be gratefully accepted.
    147                //
    148                ctor.setAccessible(true);
    149            } catch (final SecurityException se) {
    150                /* SWALLOW, if workaround fails don't fret. */
    151            }
    152            return ctor;
    153
    154        } catch (final NoSuchMethodException e) { /* SWALLOW */
    155        }
    156
    157        // search through all methods
    158        final int paramSize = parameterTypes.length;
    159        final Constructor<?>[] ctors = clazz.getConstructors();
    160        for (final Constructor<?> ctor2 : ctors) {
    161            // compare parameters
    162            final Class<?>[] ctorParams = ctor2.getParameterTypes();
    163            final int ctorParamSize = ctorParams.length;
    164            if (ctorParamSize == paramSize) {
    165                boolean match = true;
    166                for (int n = 0; n < ctorParamSize; n++) {
    167                    if (!MethodUtils.isAssignmentCompatible(ctorParams[n], parameterTypes[n])) {
    168                        match = false;
    169                        break;
    170                    }
    171                }
    172
    173                if (match) {
    174                    // get accessible version of method
    175                    final Constructor<?> ctor = getAccessibleConstructor(ctor2);
    176                    if (ctor != null) {
    177                        try {
    178                            ctor.setAccessible(true);
    179                        } catch (final SecurityException se) {
    180                            /*
    181                             * Swallow SecurityException TODO: Why?
    182                             */
    183                        }
    184                        // Class.getConstructors() actually returns constructors
    185                        // of type T, so it is safe to cast.
    186                        return (Constructor<T>) ctor;
    187                    }
    188                }
    189            }
    190        }
    191
    192        return null;
    193    }
    194
    195    /**
    196     * <p>
    197     * Convenience method returning new instance of {@code klazz} using a single argument constructor. The formal parameter type is inferred from the actual
    198     * values of {@code arg}. See {@link #invokeExactConstructor(Class, Object[], Class[])} for more details.
    199     * </p>
    200     *
    201     * <p>
    202     * The signatures should be assignment compatible.
    203     * </p>
    204     *
    205     * @param <T>   the type of the object to be constructed
    206     * @param klass the class to be constructed.
    207     * @param arg   the actual argument. May be null (this will result in calling the default constructor).
    208     * @return new instance of {@code klazz}
    209     * @throws NoSuchMethodException     If the constructor cannot be found
    210     * @throws IllegalAccessException    If an error occurs accessing the constructor
    211     * @throws InvocationTargetException If an error occurs invoking the constructor
    212     * @throws InstantiationException    If an error occurs instantiating the class
    213     * @see #invokeConstructor(Class, Object[], Class[])
    214     */
    215    public static <T> T invokeConstructor(final Class<T> klass, final Object arg)
    216            throws NoSuchMethodException, IllegalAccessException, InvocationTargetException, InstantiationException {
    217
    218        final Object[] args = toArray(arg);
    219        return invokeConstructor(klass, args);
    220    }
    221
    222    /**
    223     * <p>
    224     * Returns new instance of {@code klazz</code> created using the actual arguments <code>args}. The formal parameter types are inferred from the actual
    225     * values of {@code args}. See {@link #invokeExactConstructor(Class, Object[], Class[])} for more details.
    226     * </p>
    227     *
    228     * <p>
    229     * The signatures should be assignment compatible.
    230     * </p>
    231     *
    232     * @param <T>   the type of the object to be constructed
    233     * @param klass the class to be constructed.
    234     * @param args  actual argument array. May be null (this will result in calling the default constructor).
    235     * @return new instance of {@code klazz}
    236     * @throws NoSuchMethodException     If the constructor cannot be found
    237     * @throws IllegalAccessException    If an error occurs accessing the constructor
    238     * @throws InvocationTargetException If an error occurs invoking the constructor
    239     * @throws InstantiationException    If an error occurs instantiating the class
    240     * @see #invokeConstructor(Class, Object[], Class[])
    241     */
    242    public static <T> T invokeConstructor(final Class<T> klass, Object[] args)
    243            throws NoSuchMethodException, IllegalAccessException, InvocationTargetException, InstantiationException {
    244
    245        if (null == args) {
    246            args = BeanUtils.EMPTY_OBJECT_ARRAY;
    247        }
    248        final int arguments = args.length;
    249        final Class<?>[] parameterTypes = new Class<?>[arguments];
    250        for (int i = 0; i < arguments; i++) {
    251            parameterTypes[i] = args[i].getClass();
    252        }
    253        return invokeConstructor(klass, args, parameterTypes);
    254    }
    255
    256    /**
    257     * <p>
    258     * Returns new instance of {@code klazz} created using constructor with signature {@code parameterTypes</code> and actual arguments <code>args}.
    259     * </p>
    260     *
    261     * <p>
    262     * The signatures should be assignment compatible.
    263     * </p>
    264     *
    265     * @param <T>            the type of the object to be constructed
    266     * @param klass          the class to be constructed.
    267     * @param args           actual argument array. May be null (this will result in calling the default constructor).
    268     * @param parameterTypes parameter types array
    269     * @return new instance of {@code klazz}
    270     * @throws NoSuchMethodException     if matching constructor cannot be found
    271     * @throws IllegalAccessException    thrown on the constructor's invocation
    272     * @throws InvocationTargetException thrown on the constructor's invocation
    273     * @throws InstantiationException    thrown on the constructor's invocation
    274     * @see Constructor#newInstance
    275     */
    276    public static <T> T invokeConstructor(final Class<T> klass, Object[] args, Class<?>[] parameterTypes)
    277            throws NoSuchMethodException, IllegalAccessException, InvocationTargetException, InstantiationException {
    278
    279        if (parameterTypes == null) {
    280            parameterTypes = BeanUtils.EMPTY_CLASS_ARRAY;
    281        }
    282        if (args == null) {
    283            args = BeanUtils.EMPTY_OBJECT_ARRAY;
    284        }
    285
    286        final Constructor<T> ctor = getMatchingAccessibleConstructor(klass, parameterTypes);
    287        if (null == ctor) {
    288            throw new NoSuchMethodException("No such accessible constructor on object: " + klass.getName());
    289        }
    290        return ctor.newInstance(args);
    291    }
    292
    293    /**
    294     * <p>
    295     * Convenience method returning new instance of {@code klazz} using a single argument constructor. The formal parameter type is inferred from the actual
    296     * values of {@code arg}. See {@link #invokeExactConstructor(Class, Object[], Class[])} for more details.
    297     * </p>
    298     *
    299     * <p>
    300     * The signatures should match exactly.
    301     * </p>
    302     *
    303     * @param <T>   the type of the object to be constructed
    304     * @param klass the class to be constructed.
    305     * @param arg   the actual argument. May be null (this will result in calling the default constructor).
    306     * @return new instance of {@code klazz}
    307     * @throws NoSuchMethodException     If the constructor cannot be found
    308     * @throws IllegalAccessException    If an error occurs accessing the constructor
    309     * @throws InvocationTargetException If an error occurs invoking the constructor
    310     * @throws InstantiationException    If an error occurs instantiating the class
    311     * @see #invokeExactConstructor(Class, Object[], Class[])
    312     */
    313    public static <T> T invokeExactConstructor(final Class<T> klass, final Object arg)
    314            throws NoSuchMethodException, IllegalAccessException, InvocationTargetException, InstantiationException {
    315
    316        final Object[] args = toArray(arg);
    317        return invokeExactConstructor(klass, args);
    318    }
    319
    320    /**
    321     * <p>
    322     * Returns new instance of {@code klazz</code> created using the actual arguments <code>args}. The formal parameter types are inferred from the actual
    323     * values of {@code args}. See {@link #invokeExactConstructor(Class, Object[], Class[])} for more details.
    324     * </p>
    325     *
    326     * <p>
    327     * The signatures should match exactly.
    328     * </p>
    329     *
    330     * @param <T>   the type of the object to be constructed
    331     * @param klass the class to be constructed.
    332     * @param args  actual argument array. May be null (this will result in calling the default constructor).
    333     * @return new instance of {@code klazz}
    334     * @throws NoSuchMethodException     If the constructor cannot be found
    335     * @throws IllegalAccessException    If an error occurs accessing the constructor
    336     * @throws InvocationTargetException If an error occurs invoking the constructor
    337     * @throws InstantiationException    If an error occurs instantiating the class
    338     * @see #invokeExactConstructor(Class, Object[], Class[])
    339     */
    340    public static <T> T invokeExactConstructor(final Class<T> klass, Object[] args)
    341            throws NoSuchMethodException, IllegalAccessException, InvocationTargetException, InstantiationException {
    342
    343        if (null == args) {
    344            args = BeanUtils.EMPTY_OBJECT_ARRAY;
    345        }
    346        final int arguments = args.length;
    347        final Class<?>[] parameterTypes = new Class[arguments];
    348        for (int i = 0; i < arguments; i++) {
    349            parameterTypes[i] = args[i].getClass();
    350        }
    351        return invokeExactConstructor(klass, args, parameterTypes);
    352    }
    353
    354    /**
    355     * <p>
    356     * Returns new instance of {@code klazz} created using constructor with signature {@code parameterTypes} and actual arguments {@code args}.
    357     * </p>
    358     *
    359     * <p>
    360     * The signatures should match exactly.
    361     * </p>
    362     *
    363     * @param <T>            the type of the object to be constructed
    364     * @param klass          the class to be constructed.
    365     * @param args           actual argument array. May be null (this will result in calling the default constructor).
    366     * @param parameterTypes parameter types array
    367     * @return new instance of {@code klazz}
    368     * @throws NoSuchMethodException     if matching constructor cannot be found
    369     * @throws IllegalAccessException    thrown on the constructor's invocation
    370     * @throws InvocationTargetException thrown on the constructor's invocation
    371     * @throws InstantiationException    thrown on the constructor's invocation
    372     * @see Constructor#newInstance
    373     */
    374    public static <T> T invokeExactConstructor(final Class<T> klass, Object[] args, Class<?>[] parameterTypes)
    375            throws NoSuchMethodException, IllegalAccessException, InvocationTargetException, InstantiationException {
    376
    377        if (args == null) {
    378            args = BeanUtils.EMPTY_OBJECT_ARRAY;
    379        }
    380
    381        if (parameterTypes == null) {
    382            parameterTypes = BeanUtils.EMPTY_CLASS_ARRAY;
    383        }
    384
    385        final Constructor<T> ctor = getAccessibleConstructor(klass, parameterTypes);
    386        if (null == ctor) {
    387            throw new NoSuchMethodException("No such accessible constructor on object: " + klass.getName());
    388        }
    389        return ctor.newInstance(args);
    390    }
    391
    392    /**
    393     * Delegates to {@link Array#newInstance(Class, int)}.
    394     *
    395     * @param <T>           Component type.
    396     * @param componentType See {@link Array#newInstance(Class, int)}.
    397     * @param length        See {@link Array#newInstance(Class, int)}.
    398     * @return See {@link Array#newInstance(Class, int)}.
    399     */
    400    @SuppressWarnings("unchecked")
    401    public static <T> T[] newArray(final Class<T> componentType, final int length) {
    402        return (T[]) Array.newInstance(componentType, length);
    403    }
    404
    405    private static Object[] toArray(final Object arg) {
    406        Object[] args = null;
    407        if (arg != null) {
    408            args = new Object[] { arg };
    409        }
    410        return args;
    411    }
    412
    413}