/*
 * 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.spi;

import org.apache.logging.log4j.LogManager;
import org.apache.logging.log4j.Logger;
import org.apache.logging.log4j.ThreadContext;
import org.apache.logging.log4j.status.StatusLogger;
import org.apache.logging.log4j.util.Constants;
import org.apache.logging.log4j.util.PropertiesUtil;
import org.apache.logging.log4j.util.ProviderUtil;

Creates the ThreadContextMap instance used by the ThreadContext.
 If Log4j can use ThreadLocals, a garbage-free StringMap-based context map can be installed by setting system property log4j2.garbagefree.threadContextMap to true. 
 Furthermore, any custom ThreadContextMap can be installed by setting system property log4j2.threadContextMap to the fully qualified class name of the class implementing the ThreadContextMap interface. (Also implement the ReadOnlyThreadContextMap interface if your custom ThreadContextMap implementation should be accessible to applications via the ThreadContext.getThreadContextMap() method.) 
 Instead of system properties, the above can also be specified in a properties file named log4j2.component.properties in the classpath. 
See Also:
ThreadContextMap
ReadOnlyThreadContextMap
ThreadContext
Since:
2.7/**
 * Creates the ThreadContextMap instance used by the ThreadContext.
 * <p>
 * If {@link Constants#ENABLE_THREADLOCALS Log4j can use ThreadLocals}, a garbage-free StringMap-based context map can
 * be installed by setting system property {@code log4j2.garbagefree.threadContextMap} to {@code true}.
 * </p><p>
 * Furthermore, any custom {@code ThreadContextMap} can be installed by setting system property
 * {@code log4j2.threadContextMap} to the fully qualified class name of the class implementing the
 * {@code ThreadContextMap} interface. (Also implement the {@code ReadOnlyThreadContextMap} interface if your custom
 * {@code ThreadContextMap} implementation should be accessible to applications via the
 * {@link ThreadContext#getThreadContextMap()} method.)
 * </p><p>
 * Instead of system properties, the above can also be specified in a properties file named
 * {@code log4j2.component.properties} in the classpath.
 * </p>
 *
 * @see ThreadContextMap
 * @see ReadOnlyThreadContextMap
 * @see org.apache.logging.log4j.ThreadContext
 * @since 2.7
 */
public final class ThreadContextMapFactory {
    private static final Logger LOGGER = StatusLogger.getLogger();
    private static final String THREAD_CONTEXT_KEY = "log4j2.threadContextMap";
    private static final String GC_FREE_THREAD_CONTEXT_KEY = "log4j2.garbagefree.threadContextMap";
    
    private static boolean GcFreeThreadContextKey;
    private static String ThreadContextMapName;

    static {
        initPrivate();
    }
    
    
Initializes static variables based on system properties. Normally called when this class is initialized by the VM
and when Log4j is reconfigured.
/**
     * Initializes static variables based on system properties. Normally called when this class is initialized by the VM
     * and when Log4j is reconfigured.
     */
    public static void init() {
        CopyOnWriteSortedArrayThreadContextMap.init();
        GarbageFreeSortedArrayThreadContextMap.init();
        DefaultThreadContextMap.init();
        initPrivate();
    }

    
Initializes static variables based on system properties. Normally called when this class is initialized by the VM
and when Log4j is reconfigured.
/**
     * Initializes static variables based on system properties. Normally called when this class is initialized by the VM
     * and when Log4j is reconfigured.
     */
    private static void initPrivate() {
        final PropertiesUtil properties = PropertiesUtil.getProperties();
        ThreadContextMapName = properties.getStringProperty(THREAD_CONTEXT_KEY);
        GcFreeThreadContextKey = properties.getBooleanProperty(GC_FREE_THREAD_CONTEXT_KEY);
    }
    
    private ThreadContextMapFactory() {
    }

    public static ThreadContextMap createThreadContextMap() {
        final ClassLoader cl = ProviderUtil.findClassLoader();
        ThreadContextMap result = null;
        if (ThreadContextMapName != null) {
            try {
                final Class<?> clazz = cl.loadClass(ThreadContextMapName);
                if (ThreadContextMap.class.isAssignableFrom(clazz)) {
                    result = (ThreadContextMap) clazz.newInstance();
                }
            } catch (final ClassNotFoundException cnfe) {
                LOGGER.error("Unable to locate configured ThreadContextMap {}", ThreadContextMapName);
            } catch (final Exception ex) {
                LOGGER.error("Unable to create configured ThreadContextMap {}", ThreadContextMapName, ex);
            }
        }
        if (result == null && ProviderUtil.hasProviders() && LogManager.getFactory() != null) { //LOG4J2-1658
            final String factoryClassName = LogManager.getFactory().getClass().getName();
            for (final Provider provider : ProviderUtil.getProviders()) {
                if (factoryClassName.equals(provider.getClassName())) {
                    final Class<? extends ThreadContextMap> clazz = provider.loadThreadContextMap();
                    if (clazz != null) {
                        try {
                            result = clazz.newInstance();
                            break;
                        } catch (final Exception e) {
                            LOGGER.error("Unable to locate or load configured ThreadContextMap {}",
                                    provider.getThreadContextMap(), e);
                            result = createDefaultThreadContextMap();
                        }
                    }
                }
            }
        }
        if (result == null) {
            result = createDefaultThreadContextMap();
        }
        return result;
    }

    private static ThreadContextMap createDefaultThreadContextMap() {
        if (Constants.ENABLE_THREADLOCALS) {
            if (GcFreeThreadContextKey) {
                return new GarbageFreeSortedArrayThreadContextMap();
            }
            return new CopyOnWriteSortedArrayThreadContextMap();
        }
        return new DefaultThreadContextMap(true);
    }
}