    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
    018    package org.apache.logging.log4j.core.util;
    019
    020    import java.lang.reflect.AccessibleObject;
    021    import java.lang.reflect.Constructor;
    022    import java.lang.reflect.Field;
    023    import java.lang.reflect.InvocationTargetException;
    024    import java.lang.reflect.Member;
    025    import java.lang.reflect.Modifier;
    026
    027    /**
    028     * Utility class for performing common reflective operations.
    029     *
    030     * @since 2.1
    031     */
    032    public final class ReflectionUtil {
    033        private ReflectionUtil() {
    034        }
    035
    036        /**
    037         * Indicates whether or not a {@link Member} is both public and is contained in a public class.
    038         *
    039         * @param member the Member to check for public accessibility (must not be {@code null}).
    040         * @return {@code true} if {@code member} is public and contained in a public class.
    041         * @throws NullPointerException if {@code member} is {@code null}.
    042         */
    043        public static <T extends AccessibleObject & Member> boolean isAccessible(final T member) {
    044            Assert.requireNonNull(member, "No member provided");
    045            return Modifier.isPublic(member.getModifiers()) && Modifier.isPublic(member.getDeclaringClass().getModifiers());
    046        }
    047
    048        /**
    049         * Makes a {@link Member} {@link AccessibleObject#isAccessible() accessible} if the member is not public.
    050         *
    051         * @param member the Member to make accessible (must not be {@code null}).
    052         * @throws NullPointerException if {@code member} is {@code null}.
    053         */
    054        public static <T extends AccessibleObject & Member> void makeAccessible(final T member) {
    055            if (!isAccessible(member) && !member.isAccessible()) {
    056                member.setAccessible(true);
    057            }
    058        }
    059
    060        /**
    061         * Makes a {@link Field} {@link AccessibleObject#isAccessible() accessible} if it is not public or if it is final.
    062         *
    063         * <p>Note that using this method to make a {@code final} field writable will most likely not work very well due to
    064         * compiler optimizations and the like.</p>
    065         *
    066         * @param field the Field to make accessible (must not be {@code null}).
    067         * @throws NullPointerException if {@code field} is {@code null}.
    068         */
    069        public static void makeAccessible(final Field field) {
    070            Assert.requireNonNull(field, "No field provided");
    071            if ((!isAccessible(field) || Modifier.isFinal(field.getModifiers())) && !field.isAccessible()) {
    072                field.setAccessible(true);
    073            }
    074        }
    075
    076        /**
    077         * Gets the value of a {@link Field}, making it accessible if required.
    078         *
    079         * @param field    the Field to obtain a value from (must not be {@code null}).
    080         * @param instance the instance to obtain the field value from or {@code null} only if the field is static.
    081         * @return the value stored by the field.
    082         * @throws NullPointerException if {@code field} is {@code null}, or if {@code instance} is {@code null} but
    083         *                              {@code field} is not {@code static}.
    084         * @see Field#get(Object)
    085         */
    086        public static Object getFieldValue(final Field field, final Object instance) {
    087            makeAccessible(field);
    088            if (!Modifier.isStatic(field.getModifiers())) {
    089                Assert.requireNonNull(instance, "No instance given for non-static field");
    090            }
    091            try {
    092                return field.get(instance);
    093            } catch (final IllegalAccessException e) {
    094                throw new UnsupportedOperationException(e);
    095            }
    096        }
    097
    098        /**
    099         * Gets the value of a static {@link Field}, making it accessible if required.
    100         *
    101         * @param field the Field to obtain a value from (must not be {@code null}).
    102         * @return the value stored by the static field.
    103         * @throws NullPointerException if {@code field} is {@code null}, or if {@code field} is not {@code static}.
    104         * @see Field#get(Object)
    105         */
    106        public static Object getStaticFieldValue(final Field field) {
    107            return getFieldValue(field, null);
    108        }
    109
    110        /**
    111         * Sets the value of a {@link Field}, making it accessible if required.
    112         *
    113         * @param field    the Field to write a value to (must not be {@code null}).
    114         * @param instance the instance to write the value to or {@code null} only if the field is static.
    115         * @param value    the (possibly wrapped) value to write to the field.
    116         * @throws NullPointerException if {@code field} is {@code null}, or if {@code instance} is {@code null} but
    117         *                              {@code field} is not {@code static}.
    118         * @see Field#set(Object, Object)
    119         */
    120        public static void setFieldValue(final Field field, final Object instance, final Object value) {
    121            makeAccessible(field);
    122            if (!Modifier.isStatic(field.getModifiers())) {
    123                Assert.requireNonNull(instance, "No instance given for non-static field");
    124            }
    125            try {
    126                field.set(instance, value);
    127            } catch (final IllegalAccessException e) {
    128                throw new UnsupportedOperationException(e);
    129            }
    130        }
    131
    132        /**
    133         * Sets the value of a static {@link Field}, making it accessible if required.
    134         *
    135         * @param field the Field to write a value to (must not be {@code null}).
    136         * @param value the (possibly wrapped) value to write to the field.
    137         * @throws NullPointerException if {@code field} is {@code null}, or if {@code field} is not {@code static}.
    138         * @see Field#set(Object, Object)
    139         */
    140        public static void setStaticFieldValue(final Field field, final Object value) {
    141            setFieldValue(field, null, value);
    142        }
    143
    144        /**
    145         * Gets the default (no-arg) constructor for a given class.
    146         *
    147         * @param clazz the class to find a constructor for
    148         * @param <T>   the type made by the constructor
    149         * @return the default constructor for the given class
    150         * @throws IllegalStateException if no default constructor can be found
    151         */
    152        public static <T> Constructor<T> getDefaultConstructor(final Class<T> clazz) {
    153            Assert.requireNonNull(clazz, "No class provided");
    154            try {
    155                final Constructor<T> constructor = clazz.getDeclaredConstructor();
    156                makeAccessible(constructor);
    157                return constructor;
    158            } catch (final NoSuchMethodException ignored) {
    159                try {
    160                    final Constructor<T> constructor = clazz.getConstructor();
    161                    makeAccessible(constructor);
    162                    return constructor;
    163                } catch (final NoSuchMethodException e) {
    164                    throw new IllegalStateException(e);
    165                }
    166            }
    167        }
    168
    169        /**
    170         * Constructs a new {@code T} object using the default constructor of its class. Any exceptions thrown by the
    171         * constructor will be rethrown by this method, possibly wrapped in an
    172         * {@link java.lang.reflect.UndeclaredThrowableException}.
    173         *
    174         * @param clazz the class to use for instantiation.
    175         * @param <T>   the type of the object to construct.
    176         * @return a new instance of T made from its default constructor.
    177         * @throws IllegalArgumentException if the given class is abstract, an interface, an array class, a primitive type,
    178         *                                  or void
    179         * @throws IllegalStateException    if access is denied to the constructor, or there are no default constructors
    180         */
    181        public static <T> T instantiate(final Class<T> clazz) {
    182            Assert.requireNonNull(clazz, "No class provided");
    183            final Constructor<T> constructor = getDefaultConstructor(clazz);
    184            try {
    185                return constructor.newInstance();
    186            } catch (final InstantiationException e) {
    187                throw new IllegalArgumentException(e);
    188            } catch (final IllegalAccessException e) {
    189                throw new IllegalStateException(e);
    190            } catch (final InvocationTargetException e) {
    191                Throwables.rethrow(e.getCause());
    192                throw new InternalError("Unreachable");
    193            }
    194        }
    195    }