实体类

@ApiModelProperty(value = "创建时间")
@TableField(fill = FieldFill.INSERT)
private Date gmtCreate;

@ApiModelProperty(value = "更新时间")
@TableField(fill = FieldFill.INSERT_UPDATE)
private Date gmtModified;

Handler处理器

package com.qbb.zxjy.service.base.handler;

import com.baomidou.mybatisplus.core.handlers.MetaObjectHandler;
import org.apache.ibatis.reflection.MetaObject;
import org.springframework.stereotype.Component;

import java.util.Date;

/**
 * @author QiuQiu&LL
 * @create 2021-06-21  1:15
 * @Description:
 */
@Component
public class CommonMetaObjectHandler implements MetaObjectHandler {

    @Override
    public void insertFill(MetaObject metaObject) {
        this.setFieldValByName("gmtCreate", new Date(), metaObject);
        this.setFieldValByName("gmtModified", new Date(), metaObject);
    }

    @Override
    public void updateFill(MetaObject metaObject) {
        this.setFieldValByName("gmtModified", new Date(), metaObject);
    }
}

测试