code: /*
   * 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.skywalking.oap.server.core.logging;
  
  import com.google.common.base.Strings;
  import java.io.ByteArrayInputStream;
  import java.io.IOException;
  import lombok.extern.slf4j.Slf4j;
  import org.apache.logging.log4j.LogManager;
  import org.apache.logging.log4j.core.LoggerContext;
  import org.apache.logging.log4j.core.config.ConfigurationSource;
  import org.apache.logging.log4j.core.config.xml.XmlConfiguration;
  import org.apache.skywalking.oap.server.configuration.api.ConfigChangeWatcher;
  import org.apache.skywalking.oap.server.core.CoreModule;
  import org.apache.skywalking.oap.server.core.logging.log4j.OapConfiguration;
  import org.apache.skywalking.oap.server.library.module.ModuleProvider;
  
  /**
   * LoggingConfigWatcher watches the change of logging configuration. Once got the change content, it would apply them to
   * the current logger context.
   */
  @Slf4j
  public class LoggingConfigWatcher extends ConfigChangeWatcher {
      private final LoggerContext ctx;
      private final XmlConfiguration originConfiguration;
      private volatile String content;
  
      public LoggingConfigWatcher(final ModuleProvider provider) {
          super(CoreModule.NAME, provider, "log4j-xml");
          this.ctx = (LoggerContext) LogManager.getContext(false);
          this.originConfiguration = (XmlConfiguration) ctx.getConfiguration();
      }
  
      @Override
      public void notify(final ConfigChangeEvent value) {
          String newValue;
          if (EventType.DELETE.equals(value.getEventType())) {
              this.content = null;
              newValue = null;
          } else {
              this.content = value.getNewValue();
              newValue = value.getNewValue();
          }
          try {
              if (!reconfigure(newValue)) {
                  return;
              }
          } catch (Throwable t) {
              log.error("failed to apply configuration to log4j", t);
              return;
          }
      }
  
      @Override
      public String value() {
          return this.content;
      }
  
      private boolean reconfigure(final String newValue) {
          if (Strings.isNullOrEmpty(newValue)) {
              if (ctx.getConfiguration().equals(originConfiguration)) {
                  return false;
              }
              ctx.onChange(originConfiguration);
              return true;
          }
          OapConfiguration oc;
          try {
              oc = new OapConfiguration(ctx, new ConfigurationSource(new ByteArrayInputStream(newValue.getBytes())));
          } catch (IOException e) {
              throw new RuntimeException(String.format("failed to parse %s from configuration center", newValue), e);
          }
          oc.initialize();
          ctx.onChange(oc);
          return true;
      }
  }
  