/*
    * 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.log4j.pattern;
  
  import org.apache.logging.log4j.core.LogEvent;
  import org.apache.logging.log4j.core.config.plugins.Plugin;
  import org.apache.logging.log4j.core.pattern.ConverterKeys;
  import org.apache.logging.log4j.core.pattern.LogEventPatternConverter;
  import org.apache.logging.log4j.core.pattern.PatternConverter;
  import org.apache.logging.log4j.util.Strings;
  
  import java.util.List;
  
  
  /**
   * Returns the event's NDC in a StringBuilder.
   */
  @Plugin(name = "Log4j1NdcPatternConverter", category = PatternConverter.CATEGORY)
  @ConverterKeys({ "ndc" })
  public final class Log4j1NdcPatternConverter extends LogEventPatternConverter {
      /**
       * Singleton.
       */
      private static final Log4j1NdcPatternConverter INSTANCE =
          new Log4j1NdcPatternConverter();
  
      /**
       * Private constructor.
       */
      private Log4j1NdcPatternConverter() {
          super("Log4j1NDC", "ndc");
      }
  
      /**
       * Obtains an instance of NdcPatternConverter.
       *
       * @param options options, may be null.
       * @return instance of NdcPatternConverter.
       */
      public static Log4j1NdcPatternConverter newInstance(final String[] options) {
          return INSTANCE;
      }
  
      @Override
      public void format(final LogEvent event, final StringBuilder toAppendTo) {
          final List<String> ndc = event.getContextStack().asList();
          toAppendTo.append(Strings.join(ndc, ' '));
      }
  }