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.logging.log4j.core.util;
019
020import java.lang.reflect.AccessibleObject;
021import java.lang.reflect.Constructor;
022import java.lang.reflect.Field;
023import java.lang.reflect.InvocationTargetException;
024import java.lang.reflect.Member;
025import java.lang.reflect.Modifier;
026
027/**
028 * Utility class for performing common reflective operations.
029 *
030 * @since 2.1
031 */
032public 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}