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 }