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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.spi;

import java.net.URL;
import java.util.Properties;

import org.apache.logging.log4j.Logger;
import org.apache.logging.log4j.status.StatusLogger;

/**
 * Model class for a Log4j 2 provider. The properties in this class correspond to the properties used in a
 * {@code META-INF/log4j-provider.properties} file. Note that this class is automatically created by Log4j and should
 * not be used by providers.
 */
public class Provider {
    private static final Integer DEFAULT_PRIORITY = Integer.valueOf(-1);
    /**
     * Property name to set for a Log4j 2 provider to specify the priority of this implementation.
     */
    public static final String FACTORY_PRIORITY = "FactoryPriority";
    /**
     * Property name to set to the implementation of {@link org.apache.logging.log4j.spi.ThreadContextMap}.
     */
    public static final String THREAD_CONTEXT_MAP = "ThreadContextMap";
    /**
     * Property name to set to the implementation of {@link org.apache.logging.log4j.spi.LoggerContextFactory}.
     */
    public static final String LOGGER_CONTEXT_FACTORY = "LoggerContextFactory";

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

    private final Integer priority;
    private final String className;
    private final String threadContextMap;
    private final URL url;
    private final ClassLoader classLoader;

    public Provider(final Properties props, final URL url, final ClassLoader classLoader) {
        this.url = url;
        this.classLoader = classLoader;
        final String weight = props.getProperty(FACTORY_PRIORITY);
        priority = weight == null ? DEFAULT_PRIORITY : Integer.valueOf(weight);
        className = props.getProperty(LOGGER_CONTEXT_FACTORY);
        threadContextMap = props.getProperty(THREAD_CONTEXT_MAP);
    }

    /**
     * Gets the priority (natural ordering) of this Provider.
     *
     * @return the priority of this Provider
     */
    public Integer getPriority() {
        return priority;
    }

    /**
     * Gets the class name of the {@link org.apache.logging.log4j.spi.LoggerContextFactory} implementation of this
     * Provider.
     *
     * @return the class name of a LoggerContextFactory implementation
     */
    public String getClassName() {
        return className;
    }

    /**
     * Loads the {@link org.apache.logging.log4j.spi.LoggerContextFactory} class specified by this Provider.
     *
     * @return the LoggerContextFactory implementation class or {@code null} if there was an error loading it
     */
    @SuppressWarnings("unchecked")
    public Class loadLoggerContextFactory() {
        if (className == null) {
            return null;
        }
        try {
            final Class clazz = classLoader.loadClass(className);
            if (LoggerContextFactory.class.isAssignableFrom(clazz)) {
                return (Class) clazz;
            }
        } catch (final Exception e) {
            LOGGER.error("Unable to create class {} specified in {}", className, url.toString(), e);
        }
        return null;
    }

    /**
     * Gets the class name of the {@link org.apache.logging.log4j.spi.ThreadContextMap} implementation of this
     * Provider.
     *
     * @return the class name of a ThreadContextMap implementation
     */
    public String getThreadContextMap() {
        return threadContextMap;
    }

    /**
     * Loads the {@link org.apache.logging.log4j.spi.ThreadContextMap} class specified by this Provider.
     *
     * @return the ThreadContextMap implementation class or {@code null} if there was an error loading it
     */
    @SuppressWarnings("unchecked")
    public Class loadThreadContextMap() {
        if (threadContextMap == null) {
            return null;
        }
        try {
            final Class clazz = classLoader.loadClass(threadContextMap);
            if (ThreadContextMap.class.isAssignableFrom(clazz)) {
                return (Class) clazz;
            }
        } catch (final Exception e) {
            LOGGER.error("Unable to create class {} specified in {}", threadContextMap, url.toString(), e);
        }
        return null;
    }

    /**
     * Gets the URL containing this Provider's Log4j details.
     *
     * @return the URL corresponding to the Provider {@code META-INF/log4j-provider.properties} file
     */
    public URL getUrl() {
        return url;
    }
}