content: /*
   * Copyright 1999-2023 Alibaba Group Holding Ltd.
   *
   * Licensed 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 com.alibaba.nacos.auth.serveridentity;
  
  import com.alibaba.nacos.common.spi.NacosServiceLoader;
  import org.slf4j.Logger;
  import org.slf4j.LoggerFactory;
  
  import java.lang.reflect.InvocationTargetException;
  import java.util.Collection;
  
  /**
   * Server Identity Checker SPI holder.
   *
   * @author xiweng.yy
   */
  public class ServerIdentityCheckerHolder {
      
      private static final Logger LOGGER = LoggerFactory.getLogger(ServerIdentityCheckerHolder.class);
      
      private static final ServerIdentityCheckerHolder INSTANCE = new ServerIdentityCheckerHolder();
      
      private Class<? extends ServerIdentityChecker> checkerClass;
      
      private ServerIdentityCheckerHolder() {
          tryGetCheckerBySpi();
      }
      
      public static ServerIdentityCheckerHolder getInstance() {
          return INSTANCE;
      }
      
      /**
       * Build a new checker.
       *
       * @return new checker instance.
       */
      public ServerIdentityChecker newChecker() {
          try {
              return checkerClass.getDeclaredConstructor(new Class[0]).newInstance();
          } catch (InstantiationException | IllegalAccessException | InvocationTargetException | NoSuchMethodException e) {
              return new DefaultChecker();
          }
      }
      
      private synchronized void tryGetCheckerBySpi() {
          Collection<ServerIdentityChecker> checkers = NacosServiceLoader.load(ServerIdentityChecker.class);
          if (checkers.isEmpty()) {
              checkerClass = DefaultChecker.class;
              LOGGER.info("Not found ServerIdentityChecker implementation from SPI, use default.");
              return;
          }
          if (checkers.size() > 1) {
              checkerClass = showAllImplementations(checkers);
              return;
          }
          checkerClass = checkers.iterator().next().getClass();
          LOGGER.info("Found ServerIdentityChecker implementation {}", checkerClass.getClass().getCanonicalName());
      }
      
      private Class<? extends ServerIdentityChecker> showAllImplementations(Collection<ServerIdentityChecker> checkers) {
          ServerIdentityChecker result = checkers.iterator().next();
          for (ServerIdentityChecker each : checkers) {
              LOGGER.warn("Found ServerIdentityChecker implementation {}", each.getClass().getCanonicalName());
          }
          LOGGER.warn("Found more than one ServerIdentityChecker implementation from SPI, use the first one {}.",
                  result.getClass().getCanonicalName());
          return result.getClass();
      }
  }
  