/*
 * 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 org.apache.logging.log4j.ThreadContext;
import org.apache.logging.log4j.core.ContextDataInjector;
import org.apache.logging.log4j.core.LogEvent;
import org.apache.logging.log4j.core.util.Loader;
import org.apache.logging.log4j.spi.CopyOnWrite;
import org.apache.logging.log4j.spi.DefaultThreadContextMap;
import org.apache.logging.log4j.spi.ReadOnlyThreadContextMap;
import org.apache.logging.log4j.status.StatusLogger;
import org.apache.logging.log4j.util.PropertiesUtil;
import org.apache.logging.log4j.util.ReadOnlyStringMap;

Factory for ContextDataInjectors. Returns a new ContextDataInjector instance based on the value of system property log4j2.ContextDataInjector. Users may use this system property to specify the fully qualified class name of a class that implements the ContextDataInjector interface. If no value was specified this factory method returns one of the injectors defined in ThreadContextDataInjector. 
See Also:
ContextDataInjector
ReadOnlyStringMap
ThreadContextDataInjector
LogEvent.getContextData()
Since:
2.7/**
 * Factory for ContextDataInjectors. Returns a new {@code ContextDataInjector} instance based on the value of system
 * property {@code log4j2.ContextDataInjector}. Users may use this system property to specify the fully qualified class
 * name of a class that implements the {@code ContextDataInjector} interface.
 * If no value was specified this factory method returns one of the injectors defined in
 * {@code ThreadContextDataInjector}.
 *
 * @see ContextDataInjector
 * @see ReadOnlyStringMap
 * @see ThreadContextDataInjector
 * @see LogEvent#getContextData()
 * @since 2.7
 */
public class ContextDataInjectorFactory {

    
Returns a new ContextDataInjector instance based on the value of system property log4j2.ContextDataInjector. If no value was specified this factory method returns one of the ContextDataInjector classes defined in ThreadContextDataInjector which is most appropriate for the ThreadContext implementation. 
 Users may use this system property to specify the fully qualified class name of a class that implements the ContextDataInjector interface. 
 When providing a custom ContextDataInjector, be aware that this method may be invoked multiple times by the various components in Log4j that need access to context data. This includes the object(s) that populate log events, but also various lookups and filters that look at context data to determine whether an event should be logged. 
See Also:
LogEvent.getContextData()
ContextDataInjector
Returns:
a ContextDataInjector that populates the ReadOnlyStringMap of all LogEvent objects/**
     * Returns a new {@code ContextDataInjector} instance based on the value of system property
     * {@code log4j2.ContextDataInjector}. If no value was specified this factory method returns one of the
     * {@code ContextDataInjector} classes defined in {@link ThreadContextDataInjector} which is most appropriate for
     * the ThreadContext implementation.
     * <p>
     * Users may use this system property to specify the fully qualified class name of a class that implements the
     * {@code ContextDataInjector} interface.
     * </p><p>
     * When providing a custom {@code ContextDataInjector}, be aware that this method may be invoked multiple times by
     * the various components in Log4j that need access to context data.
     * This includes the object(s) that populate log events, but also various lookups and filters that look at
     * context data to determine whether an event should be logged.
     * </p>
     *
     * @return a ContextDataInjector that populates the {@code ReadOnlyStringMap} of all {@code LogEvent} objects
     * @see LogEvent#getContextData()
     * @see ContextDataInjector
     */
    public static ContextDataInjector createInjector() {
        final String className = PropertiesUtil.getProperties().getStringProperty("log4j2.ContextDataInjector");
        if (className == null) {
            return createDefaultInjector();
        }
        try {
            final Class<? extends ContextDataInjector> cls = Loader.loadClass(className).asSubclass(
                    ContextDataInjector.class);
            return cls.newInstance();
        } catch (final Exception dynamicFailed) {
            final ContextDataInjector result = createDefaultInjector();
            StatusLogger.getLogger().warn(
                    "Could not create ContextDataInjector for '{}', using default {}: {}",
                    className, result.getClass().getName(), dynamicFailed);
            return result;
        }
    }

    private static ContextDataInjector createDefaultInjector() {
        final ReadOnlyThreadContextMap threadContextMap = ThreadContext.getThreadContextMap();

        // note: map may be null (if legacy custom ThreadContextMap was installed by user)
        if (threadContextMap instanceof DefaultThreadContextMap || threadContextMap == null) {
            return new ThreadContextDataInjector.ForDefaultThreadContextMap(); // for non StringMap-based context maps
        }
        if (threadContextMap instanceof CopyOnWrite) {
            return new ThreadContextDataInjector.ForCopyOnWriteThreadContextMap();
        }
        return new ThreadContextDataInjector.ForGarbageFreeThreadContextMap();
    }
}