content: /*
   * Copyright 1999-2018 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.csp.sentinel.cluster.client;
  
  import com.alibaba.csp.sentinel.log.RecordLog;
  import com.alibaba.csp.sentinel.spi.SpiLoader;
  
  /**
   * Provider for a universal {@link ClusterTokenClient} instance.
   *
   * @author Eric Zhao
   * @since 1.4.0
   */
  public final class TokenClientProvider {
  
      private static ClusterTokenClient client = null;
  
      static {
          // Not strictly thread-safe, but it's OK since it will be resolved only once.
          resolveTokenClientInstance();
      }
  
      public static ClusterTokenClient getClient() {
          return client;
      }
  
      private static void resolveTokenClientInstance() {
          ClusterTokenClient resolvedClient = SpiLoader.of(ClusterTokenClient.class).loadFirstInstance();
          if (resolvedClient == null) {
              RecordLog.info(
                  "[TokenClientProvider] No existing cluster token client, cluster client mode will not be activated");
          } else {
              client = resolvedClient;
              RecordLog.info("[TokenClientProvider] Cluster token client resolved: {}",
                  client.getClass().getCanonicalName());
          }
      }
  
      public static boolean isClientSpiAvailable() {
          return getClient() != null;
      }
  
      private TokenClientProvider() {}
  }
  