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.pattern;
018    
019    import java.util.Map;
020    import java.util.Set;
021    import java.util.TreeSet;
022    
023    import org.apache.logging.log4j.core.LogEvent;
024    import org.apache.logging.log4j.core.config.plugins.Plugin;
025    
026    /**
027     * Able to handle the contents of the LogEvent's MDC and either
028     * output the entire contents of the properties in a similar format to the
029     * java.util.Hashtable.toString(), or to output the value of a specific key
030     * within the property bundle
031     * when this pattern converter has the option set.
032     */
033     @Plugin(name = "MdcPatternConverter", category = PatternConverter.CATEGORY)
034    @ConverterKeys({ "X", "mdc", "MDC" })
035    public final class MdcPatternConverter extends LogEventPatternConverter {
036        /**
037         * Name of property to output.
038         */
039        private final String key;
040    
041        /**
042         * Private constructor.
043         *
044         * @param options options, may be null.
045         */
046        private MdcPatternConverter(final String[] options) {
047            super(options != null && options.length > 0 ? "MDC{" + options[0] + '}' : "MDC", "mdc");
048            key = options != null && options.length > 0 ? options[0] : null;
049        }
050    
051        /**
052         * Obtains an instance of PropertiesPatternConverter.
053         *
054         * @param options options, may be null or first element contains name of property to format.
055         * @return instance of PropertiesPatternConverter.
056         */
057        public static MdcPatternConverter newInstance(final String[] options) {
058            return new MdcPatternConverter(options);
059        }
060    
061        /**
062         * {@inheritDoc}
063         */
064        @Override
065        public void format(final LogEvent event, final StringBuilder toAppendTo) {
066            final Map<String, String> contextMap = event.getContextMap();
067            // if there is no additional options, we output every single
068            // Key/Value pair for the MDC in a similar format to Hashtable.toString()
069            if (key == null) {
070    
071    
072                if (contextMap == null || contextMap.isEmpty()) {
073                    toAppendTo.append("{}");
074                    return;
075                }
076                final StringBuilder sb = new StringBuilder("{");
077                final Set<String> keys = new TreeSet<String>(contextMap.keySet());
078                for (final String key : keys) {
079                    if (sb.length() > 1) {
080                        sb.append(", ");
081                    }
082                    sb.append(key).append('=').append(contextMap.get(key));
083    
084                }
085                sb.append('}');
086                toAppendTo.append(sb);
087            } else if (contextMap != null) {
088                // otherwise they just want a single key output
089                final Object val = contextMap.get(key);
090    
091                if (val != null) {
092                    toAppendTo.append(val);
093                }
094            }
095        }
096    }