001    /*
002     * Licensed to the Apache Software Foundation (ASF) under one or more
003     * contributor license agreements. See the NOTICE file distributed with
004     * this work for additional information regarding copyright ownership.
005     * The ASF licenses this file to You under the Apache license, Version 2.0
006     * (the "License"); you may not use this file except in compliance with
007     * the License. You may obtain a copy of the License at
008     *
009     *      http://www.apache.org/licenses/LICENSE-2.0
010     *
011     * Unless required by applicable law or agreed to in writing, software
012     * distributed under the License is distributed on an "AS IS" BASIS,
013     * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
014     * See the license for the specific language governing permissions and
015     * limitations under the license.
016     */
017    package org.apache.logging.log4j.core.lookup;
018    
019    import org.apache.logging.log4j.core.LogEvent;
020    import org.apache.logging.log4j.core.config.plugins.Plugin;
021    
022    /**
023     * Looks up keys from environment variables.
024     */
025    @Plugin(name = "env", category = StrLookup.CATEGORY)
026    public class EnvironmentLookup extends AbstractLookup {
027    
028        /**
029         * Looks up the value of the environment variable.
030         * @param event The current LogEvent (is ignored by this StrLookup).
031         * @param key  the key to be looked up, may be null
032         * @return The value of the environment variable.
033         */
034        @Override
035        public String lookup(final LogEvent event, final String key) {
036            return System.getenv(key);
037        }
038    }