实体类基类

@MappedSuperclass
public abstract class BaseEntity {

    private LocalDateTime createdDate;
    private LocalDateTime lastModifiedDate;
    private String createdBy;
    private String lastModifiedBy;

    @PrePersist
    protected void onCreate() {
        createdDate = LocalDateTime.now();
        lastModifiedDate = createdDate;
        String currentUser = getCurrentUserFromContext();
        if (currentUser != null) {
            createdBy = currentUser;
            lastModifiedBy = currentUser;
        }
        // 如果 currentUser == null，你可以选择：
        // - 抛异常（不允许无用户操作）
        // - 设为 "SYSTEM"
        // - 或者保留 null（但首次必须有值？）
    }

    @PreUpdate
    protected void onUpdate() {
        lastModifiedDate = LocalDateTime.now();
        String currentUser = getCurrentUserFromContext();
        if (currentUser != null) {
            lastModifiedBy = currentUser;
        }
        // 👉 关键：如果 currentUser 为空，就不更新 lastModifiedBy，保留旧值！
    }

    private String getCurrentUserFromContext() {
        Authentication auth = SecurityContextHolder.getContext().getAuthentication();
        if (auth == null || !auth.isAuthenticated()) {
            return null;
        }
        Object principal = auth.getPrincipal();
        if (principal instanceof UserDetails) {
            return ((UserDetails) principal).getUsername();
        } else if (principal instanceof String) {
            return (String) principal;
        }
        return null;
    }

    // getters/setters...
}