log4j-jul/src/main/java/org/apache/logging/log4j/jul/LogManager.java

/*
 * 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.jul;

import java.util.Collections;
import java.util.Enumeration;
import java.util.HashSet;
import java.util.Set;
import java.util.logging.Logger;

import org.apache.logging.log4j.LoggingException;
import org.apache.logging.log4j.status.StatusLogger;
import org.apache.logging.log4j.util.LoaderUtil;
import org.apache.logging.log4j.util.PropertiesUtil;

/**
 * Log4j implementation of {@link java.util.logging.LogManager}. Note that the system property
 * {@code java.util.logging.manager} must be set to {@code org.apache.logging.log4j.jul.LogManager} in order to use
 * this adaptor. This LogManager requires the {@code log4j-api} library to be available. If {@code log4j-core} is
 * also available, then more features of {@link java.util.logging.Logger} are supported.
 *
 * <p>To override the default {@link AbstractLoggerAdapter} that is used, specify the Log4j property
 * {@code log4j.jul.LoggerAdapter} and set it to the fully qualified class name of a custom
 * implementation. All implementations must have a default constructor.</p>
 *
 * @since 2.1
 */
public class LogManager extends java.util.logging.LogManager {

    private static final org.apache.logging.log4j.Logger LOGGER = StatusLogger.getLogger();
    private final AbstractLoggerAdapter loggerAdapter;
    // Contains the set of logger names that are actively being requested using getLogger.
    private final ThreadLocal<Set<String>> recursive = ThreadLocal.withInitial(HashSet::new);

    public LogManager() {
        super();
        AbstractLoggerAdapter adapter = null;
        final String overrideAdaptorClassName =
            PropertiesUtil.getProperties().getStringProperty(Constants.LOGGER_ADAPTOR_PROPERTY);
        if (overrideAdaptorClassName != null) {
            try {
                LOGGER.info("Trying to use LoggerAdaptor [{}] specified by Log4j property.", overrideAdaptorClassName);
                adapter = LoaderUtil.newCheckedInstanceOf(overrideAdaptorClassName, AbstractLoggerAdapter.class);
            } catch (final Exception e) {
                LOGGER.error("Specified LoggerAdapter [{}] is incompatible.", overrideAdaptorClassName, e);
            }
        }
        if (adapter == null) {
            // default adapter
            String adapterClassName;
            try {
                // find out if log4j-core is available
                LoaderUtil.loadClass(Constants.CORE_LOGGER_CLASS_NAME);
                adapterClassName = Constants.CORE_LOGGER_ADAPTER_CLASS_NAME;
            } catch (final ClassNotFoundException ignored) {
                adapterClassName = Constants.API_LOGGER_ADAPTER_CLASS_NAME;
            }
            LOGGER.debug("Attempting to use {}", adapterClassName);
            try {
                adapter = LoaderUtil.newCheckedInstanceOf(adapterClassName, AbstractLoggerAdapter.class);
            } catch (final Exception e) {
                throw LOGGER.throwing(new LoggingException(e));
            }
        }
        loggerAdapter = adapter;
        LOGGER.info("Registered Log4j as the java.util.logging.LogManager.");
    }

    @Override
    public boolean addLogger(final Logger logger) {
        // in order to prevent non-bridged loggers from being registered, we always return false to indicate that
        // the named logger should be obtained through getLogger(name)
        return false;
    }

    @Override
    public Logger getLogger(final String name) {
        LOGGER.trace("Call to LogManager.getLogger({})", name);
        Set<String> activeRequests = recursive.get();
        if (activeRequests.add(name)) {
            try {
                return loggerAdapter.getLogger(name);
            } finally {
                activeRequests.remove(name);
            }
        } else {
            LOGGER.warn("Recursive call to getLogger for {} ignored.", name);
            return new NoOpLogger(name);
        }
    }

    @Override
    public Enumeration<String> getLoggerNames() {
        return Collections.enumeration(loggerAdapter.getLoggersInContext(loggerAdapter.getContext()).keySet());
    }

}