使用Optional来避免空指针

    /**     * 避免空指针问题     * @param resolver     * @param <T>     * @return     */    public static <T> Optional<T> resolve(Supplier<T> resolver) {        try {            T result = resolver.get();            return Optional.ofNullable(result);        } catch (NullPointerException e) {            return Optional.empty();        }    }