content: /*
   * Copyright 1999-2017 Alibaba Group.
   *
   * 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.p3c.pmd.lang.java.util;
  
  import java.util.ServiceLoader;
  import java.util.concurrent.ConcurrentHashMap;
  
  import com.alibaba.p3c.pmd.lang.java.util.namelist.NameListConfig;
  
  /**
   * @author changle.lq
   * @date 2017/04/01
   */
  public class SpiLoader {
      private final static ConcurrentHashMap<Class<?>, Object> INSTANCE_CACHE = new ConcurrentHashMap<Class<?>, Object>();
  
      @SuppressWarnings("unchecked")
      public static <T> T getInstance(Class<T> classType) {
          T instance = (T)INSTANCE_CACHE.get(classType);
  
          if (instance != null) {
              return instance;
          }
          try {
              instance = ServiceLoader.load(classType, NameListConfig.class.getClassLoader()).iterator().next();
              if (instance == null) {
                  return null;
              }
              INSTANCE_CACHE.putIfAbsent(classType, instance);
              return instance;
          } catch (Throwable e) {
              return null;
          }
      }
  }
  