給字段加注解

@ApiModelProperty(value = "創建人")
@TableField(fill = FieldFill.INSERT)
private String createBy;

@ApiModelProperty(value = "修改人")
@TableField(fill = FieldFill.INSERT_UPDATE)
private String updateBy;

實現MetaObjectHandler

import com.baomidou.mybatisplus.core.handlers.MetaObjectHandler;
import com.hrwms.common.base.UserEntity;
import com.hrwms.common.utils.UserContext;
import org.apache.ibatis.reflection.MetaObject;
import org.springframework.stereotype.Component;

@Component
public class FillHandler implements MetaObjectHandler {
    @Override
    public void insertFill(MetaObject metaObject) {
        String userName = UserContext.currentUserOpt().map(UserEntity::getUserName).orElse("sys");
        this.setFieldValByName("createBy", userName,metaObject);
    }

    @Override
    public void updateFill(MetaObject metaObject) {
        String userName = UserContext.currentUserOpt().map(UserEntity::getUserName).orElse("sys");
        this.setFieldValByName("updateBy", userName,metaObject);
    }
}

將創建的FillHandler類注入到配置中（重要）

如果項目中使用配置類創建了SqlSessionFactory，需要手動將自定義的MetaObjectHandler注入

@Bean
public SqlSessionFactory sqlSessionFactory(DataSource dataSource) throws Exception {
    MybatisSqlSessionFactoryBean mybatisSqlSessionFactoryBean = new MybatisSqlSessionFactoryBean();
    //獲取mybatis-plus全局配置
    GlobalConfig globalConfig = GlobalConfigUtils.defaults();
    //mybatis-plus全局配置設置元數據對象處理器為自己實現的那個
    globalConfig.setMetaObjectHandler(new FillHandler());
    mybatisSqlSessionFactoryBean.setDataSource(dataSource);
    //mybatisSqlSessionFactoryBean關聯設置全局配置
    mybatisSqlSessionFactoryBean.setGlobalConfig(globalConfig);
    return mybatisSqlSessionFactoryBean.getObject();
}

說明：一般在updateById、save和saveBatch api才生效

參考文章1
參考文章2