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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.impl;
import java.lang.invoke.MethodHandle;
import java.lang.invoke.MethodHandles;
import java.lang.invoke.MethodType;
import org.apache.logging.log4j.core.ContextDataInjector;
import org.apache.logging.log4j.core.LogEvent;
import org.apache.logging.log4j.util.LoaderUtil;
import org.apache.logging.log4j.util.PropertiesUtil;
import org.apache.logging.log4j.util.SortedArrayStringMap;
import org.apache.logging.log4j.util.StringMap;
/**
* Factory for creating the StringMap instances used to initialize LogEvents'
* {@linkplain LogEvent#getContextData() context data}. When context data is
* {@linkplain ContextDataInjector injected} into the log event, these StringMap
* instances may be either populated with key-value pairs from the context, or completely replaced altogether.
*
* By default returns {@code SortedArrayStringMap} objects. Can be configured by setting system property
* {@code "log4j2.ContextData"} to the fully qualified class name of a class implementing the
* {@code StringMap} interface. The class must have a public default constructor, and if possible should also have a
* public constructor that takes a single {@code int} argument for the initial capacity.
*
*
* @see LogEvent#getContextData()
* @see ContextDataInjector
* @see SortedArrayStringMap
* @since 2.7
*/
public class ContextDataFactory {
private static final MethodHandles.Lookup LOOKUP = MethodHandles.lookup();
private static final String CLASS_NAME = PropertiesUtil.getProperties().getStringProperty("log4j2.ContextData");
private static final Class CACHED_CLASS = createCachedClass(CLASS_NAME);
private static final MethodHandle DEFAULT_CONSTRUCTOR = createDefaultConstructor(CACHED_CLASS);
private static final MethodHandle INITIAL_CAPACITY_CONSTRUCTOR = createInitialCapacityConstructor(CACHED_CLASS);
private static final StringMap EMPTY_STRING_MAP = createContextData(1);
static {
EMPTY_STRING_MAP.freeze();
}
private static Class createCachedClass(final String className) {
if (className == null) {
return null;
}
try {
return LoaderUtil.loadClass(className).asSubclass(StringMap.class);
} catch (final Exception any) {
return null;
}
}
private static MethodHandle createDefaultConstructor(final Class cachedClass) {
if (cachedClass == null) {
return null;
}
try {
return LOOKUP.findConstructor(cachedClass, MethodType.methodType(void.class));
} catch (final NoSuchMethodException | IllegalAccessException ignored) {
return null;
}
}
private static MethodHandle createInitialCapacityConstructor(final Class cachedClass) {
if (cachedClass == null) {
return null;
}
try {
return LOOKUP.findConstructor(cachedClass, MethodType.methodType(void.class, int.class));
} catch (final NoSuchMethodException | IllegalAccessException ignored) {
return null;
}
}
public static StringMap createContextData() {
if (DEFAULT_CONSTRUCTOR == null) {
return new SortedArrayStringMap();
}
try {
return (StringMap) DEFAULT_CONSTRUCTOR.invoke();
} catch (final Throwable ignored) {
return new SortedArrayStringMap();
}
}
public static StringMap createContextData(final int initialCapacity) {
if (INITIAL_CAPACITY_CONSTRUCTOR == null) {
return new SortedArrayStringMap(initialCapacity);
}
try {
return (StringMap) INITIAL_CAPACITY_CONSTRUCTOR.invoke(initialCapacity);
} catch (final Throwable ignored) {
return new SortedArrayStringMap(initialCapacity);
}
}
/**
* An empty pre-frozen StringMap. The returned object may be shared.
*
* @return an empty pre-frozen StringMap
*/
public static StringMap emptyFrozenContextData() {
return EMPTY_STRING_MAP;
}
}