content: /**
   * Copyright (c) 2010-present Abixen Systems. All rights reserved.
   *
   * This library is free software; you can redistribute it and/or modify it under
   * the terms of the GNU Lesser General Public License as published by the Free
   * Software Foundation; either version 2.1 of the License, or (at your option)
   * any later version.
   *
   * This library is distributed in the hope that it will be useful, but WITHOUT
   * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
   * FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public License for more
   * details.
   */
  
  package com.abixen.platform.client.web.controller;
  
  import java.util.Map;
  import java.util.concurrent.ConcurrentHashMap;
  import java.util.function.Function;
  import java.util.function.Predicate;
  
  
  public class BaseController {
  
      protected <T> Predicate<T> distinctByKey(Function<? super T, Object> keyExtractor) {
          Map<Object, Boolean> seen = new ConcurrentHashMap<>();
          return t -> seen.putIfAbsent(keyExtractor.apply(t), Boolean.TRUE) == null;
      }
  }