SpringBoot使用MybatisPlus的正确姿势

一 背景

• 你的SpringBoot项目中使用Mybatis是否还是需要自己写一堆xmlmapper和sql，经常新增一个字段，要改多个地方且容易改错（entity、mapper）。
• 你是否经常在代码中重复公共字段的设置，如创建时间、修改时间、修改人、创建人等等公共信息。
• 你是否在使用mybatis的时候，为了防止并发更新，要手动去控制version乐观锁。

以上问题，只要你使用了MybatisPlus，就能很好的解决，具体的一个实践请参考下面的博文。更多文档参考github：https://github.com/baomidou/mybatis-plus

二 实践步骤1 pom依赖

<!-- https://mvnrepository.com/artifact/com.baomidou/mybatis-plus -->
<dependency>
    <groupId>com.baomidou</groupId>
    <artifactId>mybatis-plus-boot-starter</artifactId>
    <version>3.3.0</version>
</dependency>

三 实践步骤2 自动填充

import com.baomidou.mybatisplus.annotation.FieldFill;
import com.baomidou.mybatisplus.annotation.IdType;
import com.baomidou.mybatisplus.annotation.TableId;
import com.baomidou.mybatisplus.annotation.TableField;
import com.baomidou.mybatisplus.annotation.TableLogic;
import com.baomidou.mybatisplus.extension.activerecord.Model;
import lombok.Data;

import java.util.Date;

@Data
public class BaseEntity extends Model {
    @TableId(value = "id", type = IdType.AUTO)
    private Long id;
    /**
     * 创建者
     */
    @TableField(fill = FieldFill.INSERT)
    private String createdBy;
    /**
     * 创建时间
     */
    @TableField(fill = FieldFill.INSERT)
    private Date createdDate;
    /**
     * 修改者
     */
    @TableField(fill = FieldFill.INSERT_UPDATE)
    private String lastModifiedBy;
    /**
     * 修改时间
     */
    @TableField(fill = FieldFill.INSERT_UPDATE)
    private Date lastModifiedDate;

    @TableField
    @Version
    private Integer version;

    @TableField(fill = FieldFill.INSERT)
    @TableLogic(value = "0", delval = "1")
    private Integer deleteFlag;

    @Override
    protected Serializable pkVal() {
        return this.id;
    }
}

import com.baomidou.mybatisplus.core.handlers.MetaObjectHandler;
import com.mafgwo.common.utils.webflux.UserSecurityUtil;
import org.apache.commons.lang.StringUtils;
import org.apache.ibatis.reflection.MetaObject;

import java.lang.reflect.Field;
import java.util.Arrays;
import java.util.Date;
import java.util.Set;
import java.util.stream.Collectors;

/**
 * 填充公共字段
 * 
 * @author jacky
 * @since 2020/01/08
 */
public class AutoFillMetaObjectHandler implements MetaObjectHandler {

    private static final String FIELD_CREATED_DATE = "createdDate";
    private static final String FIELD_CREATED_BY = "createdBy";
    private static final String FIELD_LAST_MODIFIED_DATE = "lastModifiedDate";
    private static final String FIELD_LAST_MODIFIED_BY = "lastModifiedBy";
    private static final String FIELD_DELETE_FLAG = "deleteFlag";

    @Override
    public void insertFill(MetaObject metaObject) {
        Object originalObject = metaObject.getOriginalObject();
        Set<String> fieldNames = this.getAllFields(originalObject.getClass());

        String displayName = UserSecurityUtil.getDisplayName();

        if (fieldNames.contains(FIELD_CREATED_DATE)) {
            setFieldValByName(FIELD_CREATED_DATE, new Date(), metaObject);
        }
        if (fieldNames.contains(FIELD_LAST_MODIFIED_DATE)) {
            setFieldValByName(FIELD_LAST_MODIFIED_DATE, new Date(), metaObject);
        }
        if (fieldNames.contains(FIELD_CREATED_BY)) {
            setFieldValByName(FIELD_CREATED_BY, displayName, metaObject);
        }
        if (fieldNames.contains(FIELD_LAST_MODIFIED_BY)) {
            setFieldValByName(FIELD_LAST_MODIFIED_BY, displayName, metaObject);
        }
        if (fieldNames.contains(FIELD_DELETE_FLAG)) {
            setFieldValByName(FIELD_DELETE_FLAG, 0, metaObject);
        }
    }

    @Override
    public void updateFill(MetaObject metaObject) {
        Object originalObject = metaObject.getOriginalObject();
        Set<String> fieldNames = this.getAllFields(originalObject.getClass());
        String displayName = UserSecurityUtil.getDisplayName();
        if (StringUtils.isNotBlank(displayName) && fieldNames.contains(FIELD_LAST_MODIFIED_BY)) {
            Object lastModifiedBy = getFieldValByName(FIELD_LAST_MODIFIED_BY, metaObject);
            if (lastModifiedBy == null) {
                setFieldValByName(FIELD_LAST_MODIFIED_BY, displayName, metaObject);
            }
        }
        if (fieldNames.contains(FIELD_LAST_MODIFIED_DATE)) {
            Object lastModifiedDate = getFieldValByName(FIELD_LAST_MODIFIED_DATE, metaObject);
            if (lastModifiedDate == null) {
                setFieldValByName(FIELD_LAST_MODIFIED_DATE, new Date(), metaObject);
            }
        }
    }

    private Set<String> getAllFields(Class entityClass) {
        Field[] declaredFields = entityClass.getDeclaredFields();
        Set<String> fieldNames = Arrays.stream(declaredFields).map(Field::getName).collect(Collectors.toSet());

        Class<?> superclass = entityClass.getSuperclass();
        if (superclass.equals(Object.class)) {
            return fieldNames;
        }
        fieldNames.addAll(this.getAllFields(superclass));
        return fieldNames;
    }
}

四 实践步骤3 自动配置

import com.baomidou.mybatisplus.core.handlers.MetaObjectHandler;
import com.baomidou.mybatisplus.core.injector.DefaultSqlInjector;
import com.baomidou.mybatisplus.core.injector.ISqlInjector;
import com.baomidou.mybatisplus.extension.plugins.OptimisticLockerInterceptor;
import org.mybatis.spring.annotation.MapperScan;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;

/**
 * mybatis 扫描
 */
@Configuration
@MapperScan(basePackages = "com.xxxx.mapper")
public class MybatisScanAutoConfiguration {

    @Bean
    public ISqlInjector sqlInjector() {
        return new DefaultSqlInjector();
    }

    @Bean
    public MetaObjectHandler metaObjectHandler() {
        return new AutoFillMetaObjectHandler();
    }

    /**
     * 乐观锁
     * 乐观锁实现方式：
     * <p>
     * 取出记录时，获取当前version
     * 更新时，带上这个version
     * 执行更新时， set version = yourVersion+1 where version = yourVersion
     * 如果version不对，就更新失败
     *
     * @return
     */
    @Bean
    public OptimisticLockerInterceptor optimisticLockerInterceptor() {
        return new OptimisticLockerInterceptor();
    }

}

五 实践步骤4 application配置

mybatis-plus:
  mapper-locations: classpath*:/com/xxxxx/*Mapper.xml
  typeAliasesPackage: com.xxxx.entity
  configuration:
    map-underscore-to-camel-case: true

六 实践步骤5Mapper与Service使用

mapper

import com.baomidou.mybatisplus.core.mapper.BaseMapper;
import com.xxxx.entity.XXXEntity;
import org.apache.ibatis.annotations.Mapper;
import org.apache.ibatis.annotations.Select;

import java.util.List;

/**
 * mapper
 *
 * @author jacky
 * @since 2020/01/07
 */
@Mapper
public interface XXXEntityMapper extends BaseMapper<XXXEntity> {

    @Select("select * from coupon_activity_product where activity_id = #{activityId} and delete_flag = 0")
    List<XXXEntity> findByActivityId(Long activityId);
}

service-interface

import com.baomidou.mybatisplus.extension.service.IService;
import com.xxx.XXXEntity;

/**
 * service
 *
 * @author jacky
 * @since 2020/01/07
 */
public interface XXXEntityService extends IService<XXXEntity> {

}

service-impl

import com.baomidou.mybatisplus.extension.service.impl.ServiceImpl;
import com.xxx.XXXEntityVO;
import com.xxx.XXXEntityMapper;
import com.xxx.XXXEntityService;

/**
 * service
 *
 * @author jacky
 * @since 2020/01/07
 */
@Slf4j
@Service
public class XXXEntityServiceImpl extends ServiceImpl<XXXEntityMapper, XXXEntity> implements XXXEntityService {
}

7 其他说明

写到最后，虽然MybatisPlus有非常多的优点，但是很多公司（如阿里和其他一些互联网公司）都不建议使用，因为SQL这块不可控，是由mybatisplus自己拼装，可能由于传入的条件没有索引导致出现慢查询等问题。