Map

ConcurrentHashMap不支持key和value为null，containsKey也不支持传空，所以ConcurrentHashMap在put值进去和判断是否有值的时候一定要做空判断。在工作中如果使用ConcurrentHashMap时，建议使用抽出几个工具方法，省得判空方法散落在各处；

  /**
   * @param concurrentHashMap ConcurrentHashMap
   * @param key               String
   * @param value             String
   */
  public static void putValue(ConcurrentHashMap<String, Object> concurrentHashMap, String key, String value) {
      if (concurrentHashMap == null || key == null || value == null) {
          return;
      }
      concurrentHashMap.put(key, value);
  }
  /**
   * @param concurrentHashMap ConcurrentHashMap
   * @param key               String
   * @return boolean
   */
  public static boolean containsKey(ConcurrentHashMap<String, Object> concurrentHashMap, String key) {
      if (key == null || concurrentHashMap == null) {
          return false;
      }
      return concurrentHashMap.containsKey(key);
  }