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Pax Logging backend implementation based on Apache Log4J2. It provides Log4J2 specific implementation of PaxLoggingService interface and Log4J2 specific configuration methods. Users may customize Log4J2 behaviour (appenders, layouts) by creating fragment attached to this bundle.

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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.util;

import java.net.URL;
import java.security.Permission;
import java.util.List;

import org.apache.logging.log4j.Logger;
import org.apache.logging.log4j.spi.LoggerContextFactory;
import org.apache.logging.log4j.status.StatusLogger;
import org.osgi.framework.AdaptPermission;
import org.osgi.framework.AdminPermission;
import org.osgi.framework.Bundle;
import org.osgi.framework.BundleActivator;
import org.osgi.framework.BundleContext;
import org.osgi.framework.BundleEvent;
import org.osgi.framework.SynchronousBundleListener;
import org.osgi.framework.wiring.BundleWire;
import org.osgi.framework.wiring.BundleWiring;

/**
 * OSGi bundle activator. Used for locating an implementation of
 * {@link org.apache.logging.log4j.spi.LoggerContextFactory} et al. that have corresponding
 * {@code META-INF/log4j-provider.properties} files. As with all OSGi BundleActivator classes, this class is not for
 * public use and is only useful in an OSGi framework environment.
 */
public class Activator implements BundleActivator, SynchronousBundleListener {

    private static final SecurityManager SECURITY_MANAGER = System.getSecurityManager();

    private static final Logger LOGGER = StatusLogger.getLogger();

    private static void checkPermission(final Permission permission) {
        if (SECURITY_MANAGER != null) {
            SECURITY_MANAGER.checkPermission(permission);
        }
    }

    private void loadProvider(final Bundle bundle) {
        if (bundle.getState() == Bundle.UNINSTALLED) {
            return;
        }
        try {
            checkPermission(new AdminPermission(bundle, AdminPermission.RESOURCE));
            checkPermission(new AdaptPermission(BundleWiring.class.getName(), bundle, AdaptPermission.ADAPT));
            loadProvider(bundle.adapt(BundleWiring.class));
        } catch (final SecurityException e) {
            LOGGER.debug("Cannot access bundle [{}] contents. Ignoring.", bundle.getSymbolicName(), e);
        } catch (final Exception e) {
            LOGGER.warn("Problem checking bundle {} for Log4j 2 provider.", bundle.getSymbolicName(), e);
        }
    }

    private void loadProvider(BundleWiring provider) {
        final List urls = provider.findEntries("META-INF", "log4j-provider.properties", 0);
        for (final URL url : urls) {
            ProviderUtil.loadProvider(url, provider.getClassLoader());
        }
    }

    @Override
    public void start(final BundleContext context) throws Exception {
        final BundleWiring self = context.getBundle().adapt(BundleWiring.class);
        final List required = self.getRequiredWires(LoggerContextFactory.class.getName());
        for (BundleWire wire : required) {
            loadProvider(wire.getProviderWiring());
        }
        context.addBundleListener(this);
        final Bundle[] bundles = context.getBundles();
        for (final Bundle bundle : bundles) {
            loadProvider(bundle);
        }
    }

    @Override
    public void stop(final BundleContext context) throws Exception {
        context.removeBundleListener(this);
    }

    @Override
    public void bundleChanged(final BundleEvent event) {
        switch (event.getType()) {
            case BundleEvent.STARTED:
                // FIXME: LogManager won't see this update if it happens after LogManager is loaded
                loadProvider(event.getBundle());
                break;

            default:
                break;
        }
    }

}