/** * Returns a single entity matching the given {@link Example} or {@literal null} if none was found. * * @param example must not be {@literal null}. * @return a single entity matching the given {@link Example} or {@link Optional#empty()} if none was found. * @throws org.springframework.dao.IncorrectResultSizeDataAccessException if the Example yields more than one result. */ <S extends T> Optional<S> findOne(Example<S> example); /** * Returns a reference to the entity with the given identifier. * * @param id must not be {@literal null}. * @return a reference to the entity with the given identifier. * @see EntityManager#getReference(Class, Object) * @throws javax.persistence.EntityNotFoundException if no entity exists for given {@code id}. */ T getOne(ID id);
findone：返回實體的optional對象
getone：返回實體的引用，代理對象
實體轉json的過程中會出錯，用debug查看實體其實是空，數據是放在代理對象中的，但jackson將實體轉json沒有拿到代理對象，然后產生以下錯誤，這時候json轉換失敗再導致輸出流報錯。
getOne示例：
