hibernte @UpdateTimestamp自动设置更新时间出现的奇怪问题！请高手解答。

Question

/**
     * 创建时间
     */
    @Temporal(TemporalType.TIMESTAMP)
    @CreationTimestamp
    @Column(name = "CREATIONTIME", nullable=false,updatable = false)    
    @JsonFormat(pattern = "yyyy-MM-dd HH:mm:ss", timezone = "GMT+8")
    private Date creationTime;
 
    /**
     * 修改时间
     */
    @Temporal(TemporalType.TIMESTAMP)
    @UpdateTimestamp
    @Column(name = "MODIFIEDTIME", nullable = true,insertable=false)    
    @JsonFormat(pattern = "yyyy-MM-dd HH:mm:ss", timezone = "GMT+8")
    private Date modifiedTime;
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