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.nacos.naming.selector;
  
  import com.alibaba.nacos.naming.core.Instance;
  
  import java.util.List;
  
  /**
   * Selector defines a rule for load-balance for service discovery.
   * <p>
   * Every service in Nacos can apply an existing selector and uses it to give the consumer
   * a subset of selected providers.
   * <p>
   * This selector itself does not implement any specific behavior of load-balance, every
   * real life selector should extend this class and implement the select method.
   * <p>
   * Every extended selector should also register its type to class SelectorType so Nacos
   * recognizes it and can correctly create this type of selector.
   *
   * @author nkorange
   * @see com.alibaba.nacos.api.selector.SelectorType
   * @see SelectorJsonAdapter
   * @since 0.7.0
   */
  public interface Selector {
  
      /**
       * Get the type of this selector
       *
       * @return type of selector
       */
      String getType();
  
      /**
       * Select qualified instances from providers
       *
       * @param consumer  consumer address
       * @param providers candidate provider addresses
       * @return selected provider addresses
       */
      List<Instance> select(String consumer, List<Instance> providers);
  }
  