@Column(nullable=false) 是生成模式的指令。从该类生成的数据库列将在实际数据库中标记为不可空。

optional=false 是一条运行时指令。它的主要功能与懒加载有关。除非你记得设置 optional=false，否则你就无法懒加载一个非集合映射实体（因为 Hibernate 不知道那里应该有一个代理还是一个空值，除非你告诉它空值是不可能的，所以它可以生成一个代理）。

https://stackoverflow.com/questions/3331907/what-is-the-difference-between-manytooneoptional-false-vs-columnnullable-f

1. Overview

Starting with Java 8, we have a new Date API: java.time.

However, sometimes we still need to perform conversions between the new and old APIs, and work with date representations from both.

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1.Get the User in a Bean

The simplest way to retrieve the currently authenticated principal is via a static call to the SecurityContextHolder:

Authentication authentication = SecurityContextHolder.getContext().getAuthentication();
String currentPrincipalName = authentication.getName();

An improvement to this snippet is first checking if there is an authenticated user before trying to access it:

Authentication authentication = SecurityContextHolder.getContext().getAuthentication();
if (!(authentication instanceof AnonymousAuthenticationToken)) {
    String currentUserName = authentication.getName();
    return currentUserName;
}

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