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The Pax Logging API Library is to allow for the Pax Logging Service to be reloaded without stopping the many dependent bundles. It also contains the OSGi Log Service API and the Knopflerfish Log API.

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/*
 * 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 java.util.Map;
import java.util.WeakHashMap;
import java.util.concurrent.ConcurrentHashMap;
import java.util.concurrent.ConcurrentMap;

import org.apache.logging.log4j.LogManager;
import org.apache.logging.log4j.util.LoaderUtil;

/**
 * Provides an abstract base class to use for implementing LoggerAdapter.
 * 
 * @param  the Logger class to adapt
 * @since 2.1
 */
public abstract class AbstractLoggerAdapter implements LoggerAdapter {

    /**
     * A map to store loggers for their given LoggerContexts.
     */
    protected final Map> registry = new WeakHashMap<>();

    @Override
    public L getLogger(final String name) {
        final LoggerContext context = getContext();
        final ConcurrentMap loggers = getLoggersInContext(context);
        final L logger = loggers.get(name);
        if (logger != null) {
            return logger;
        }
        loggers.putIfAbsent(name, newLogger(name, context));
        return loggers.get(name);
    }

    /**
     * Gets or creates the ConcurrentMap of named loggers for a given LoggerContext.
     *
     * @param context the LoggerContext to get loggers for
     * @return the map of loggers for the given LoggerContext
     */
    public ConcurrentMap getLoggersInContext(final LoggerContext context) {
        synchronized (registry) {
            ConcurrentMap loggers = registry.get(context);
            if (loggers == null) {
                loggers = new ConcurrentHashMap<>();
                registry.put(context, loggers);
            }
            return loggers;
        }
    }

    /**
     * Creates a new named logger for a given {@link LoggerContext}.
     *
     * @param name the name of the logger to create
     * @param context the LoggerContext this logger will be associated with
     * @return the new named logger
     */
    protected abstract L newLogger(final String name, final LoggerContext context);

    /**
     * Gets the {@link LoggerContext} that should be used to look up or create loggers. This is similar in spirit to the
     * {@code ContextSelector} class in {@code log4j-core}. However, implementations can rely on their own framework's
     * separation of contexts instead (or simply use a singleton).
     *
     * @return the LoggerContext to be used for lookup and creation purposes
     * @see org.apache.logging.log4j.LogManager#getContext(ClassLoader, boolean)
     * @see org.apache.logging.log4j.LogManager#getContext(String, boolean)
     */
    protected abstract LoggerContext getContext();

    /**
     * Gets the {@link LoggerContext} associated with the given caller class.
     *
     * @param callerClass the caller class
     * @return the LoggerContext for the calling class
     */
    protected LoggerContext getContext(final Class callerClass) {
        ClassLoader cl = null;
        if (callerClass != null) {
            cl = callerClass.getClassLoader();
        }
        if (cl == null) {
            cl = LoaderUtil.getThreadContextClassLoader();
        }
        return LogManager.getContext(cl, false);
    }

    @Override
    public void close() {
        registry.clear();
    }
}