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The Apache Log4j Implementation
/*
* Licensed to the Apache Software Foundation (ASF) under one or more
* contributor license agreements. See the NOTICE file distributed with
* this work for additional information regarding copyright ownership.
* The ASF licenses this file to You under the Apache license, Version 2.0
* (the "License"); you may not use this file except in compliance with
* the License. You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the license for the specific language governing permissions and
* limitations under the license.
*/
package org.apache.logging.log4j.core.util;
import java.lang.reflect.AccessibleObject;
import java.lang.reflect.Constructor;
import java.lang.reflect.Field;
import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Member;
import java.lang.reflect.Modifier;
import java.util.Objects;
/**
* Utility class for performing common reflective operations.
*
* @since 2.1
*/
public final class ReflectionUtil {
private ReflectionUtil() {
}
/**
* Indicates whether or not a {@link Member} is both public and is contained in a public class.
*
* @param type of the object whose accessibility to test
* @param member the Member to check for public accessibility (must not be {@code null}).
* @return {@code true} if {@code member} is public and contained in a public class.
* @throws NullPointerException if {@code member} is {@code null}.
*/
public static boolean isAccessible(final T member) {
Objects.requireNonNull(member, "No member provided");
return Modifier.isPublic(member.getModifiers()) && Modifier.isPublic(member.getDeclaringClass().getModifiers());
}
/**
* Makes a {@link Member} {@link AccessibleObject#isAccessible() accessible} if the member is not public.
*
* @param type of the object to make accessible
* @param member the Member to make accessible (must not be {@code null}).
* @throws NullPointerException if {@code member} is {@code null}.
*/
public static void makeAccessible(final T member) {
if (!isAccessible(member) && !member.isAccessible()) {
member.setAccessible(true);
}
}
/**
* Makes a {@link Field} {@link AccessibleObject#isAccessible() accessible} if it is not public or if it is final.
*
* Note that using this method to make a {@code final} field writable will most likely not work very well due to
* compiler optimizations and the like.
*
* @param field the Field to make accessible (must not be {@code null}).
* @throws NullPointerException if {@code field} is {@code null}.
*/
public static void makeAccessible(final Field field) {
Objects.requireNonNull(field, "No field provided");
if ((!isAccessible(field) || Modifier.isFinal(field.getModifiers())) && !field.isAccessible()) {
field.setAccessible(true);
}
}
/**
* Gets the value of a {@link Field}, making it accessible if required.
*
* @param field the Field to obtain a value from (must not be {@code null}).
* @param instance the instance to obtain the field value from or {@code null} only if the field is static.
* @return the value stored by the field.
* @throws NullPointerException if {@code field} is {@code null}, or if {@code instance} is {@code null} but
* {@code field} is not {@code static}.
* @see Field#get(Object)
*/
public static Object getFieldValue(final Field field, final Object instance) {
makeAccessible(field);
if (!Modifier.isStatic(field.getModifiers())) {
Objects.requireNonNull(instance, "No instance given for non-static field");
}
try {
return field.get(instance);
} catch (final IllegalAccessException e) {
throw new UnsupportedOperationException(e);
}
}
/**
* Gets the value of a static {@link Field}, making it accessible if required.
*
* @param field the Field to obtain a value from (must not be {@code null}).
* @return the value stored by the static field.
* @throws NullPointerException if {@code field} is {@code null}, or if {@code field} is not {@code static}.
* @see Field#get(Object)
*/
public static Object getStaticFieldValue(final Field field) {
return getFieldValue(field, null);
}
/**
* Sets the value of a {@link Field}, making it accessible if required.
*
* @param field the Field to write a value to (must not be {@code null}).
* @param instance the instance to write the value to or {@code null} only if the field is static.
* @param value the (possibly wrapped) value to write to the field.
* @throws NullPointerException if {@code field} is {@code null}, or if {@code instance} is {@code null} but
* {@code field} is not {@code static}.
* @see Field#set(Object, Object)
*/
public static void setFieldValue(final Field field, final Object instance, final Object value) {
makeAccessible(field);
if (!Modifier.isStatic(field.getModifiers())) {
Objects.requireNonNull(instance, "No instance given for non-static field");
}
try {
field.set(instance, value);
} catch (final IllegalAccessException e) {
throw new UnsupportedOperationException(e);
}
}
/**
* Sets the value of a static {@link Field}, making it accessible if required.
*
* @param field the Field to write a value to (must not be {@code null}).
* @param value the (possibly wrapped) value to write to the field.
* @throws NullPointerException if {@code field} is {@code null}, or if {@code field} is not {@code static}.
* @see Field#set(Object, Object)
*/
public static void setStaticFieldValue(final Field field, final Object value) {
setFieldValue(field, null, value);
}
/**
* Gets the default (no-arg) constructor for a given class.
*
* @param clazz the class to find a constructor for
* @param the type made by the constructor
* @return the default constructor for the given class
* @throws IllegalStateException if no default constructor can be found
*/
public static Constructor getDefaultConstructor(final Class clazz) {
Objects.requireNonNull(clazz, "No class provided");
try {
final Constructor constructor = clazz.getDeclaredConstructor();
makeAccessible(constructor);
return constructor;
} catch (final NoSuchMethodException ignored) {
try {
final Constructor constructor = clazz.getConstructor();
makeAccessible(constructor);
return constructor;
} catch (final NoSuchMethodException e) {
throw new IllegalStateException(e);
}
}
}
/**
* Constructs a new {@code T} object using the default constructor of its class. Any exceptions thrown by the
* constructor will be rethrown by this method, possibly wrapped in an
* {@link java.lang.reflect.UndeclaredThrowableException}.
*
* @param clazz the class to use for instantiation.
* @param the type of the object to construct.
* @return a new instance of T made from its default constructor.
* @throws IllegalArgumentException if the given class is abstract, an interface, an array class, a primitive type,
* or void
* @throws IllegalStateException if access is denied to the constructor, or there are no default constructors
* @throws InternalException wrapper of the underlying exception if checked
*/
public static T instantiate(final Class clazz) {
Objects.requireNonNull(clazz, "No class provided");
final Constructor constructor = getDefaultConstructor(clazz);
try {
return constructor.newInstance();
} catch (final LinkageError | InstantiationException e) {
// LOG4J2-1051
// On platforms like Google App Engine and Android, some JRE classes are not supported: JMX, JNDI, etc.
throw new IllegalArgumentException(e);
} catch (final IllegalAccessException e) {
throw new IllegalStateException(e);
} catch (final InvocationTargetException e) {
Throwables.rethrow(e.getCause());
throw new InternalError("Unreachable");
}
}
}