开发小知识-mybatis-plus自动填充与读写分离

Posted 2020-12-20

mybatis-plus 自动填充

说明

我们在设计表结构的时候,往往会额外添多如下几个字段

create_time【表字段】-- createTime【实体字段】 ： 创建时间

update_time【表字段】-- updateTime【实体字段】：更新时间

create_by【表字段】-- createBy 【实体字段】: 创建人

update_by【表字段】--updateBy 【实体字段】：更新人

del_flag【表字段】-- delFlag【实体字段】 : 逻辑删除标识【0:未删除、1:已删除】

在编写实体类【与数据映射】的时候，不能总在每个类上都编写上述几个属性，显得有些冗余，于是我们将这几个属性提取出来

并在对应的属性上标注mybatis-plus的填充注解，那么所有继承BaseEntity的类将会拥有createTime,updateTime属性，继承DefaultEntity的类将会拥有createTime、updateTime、createBy、updateBy、delFlag属性。

至于为什么会设计两个类，是因为有些中间表可能不需要用到createBy、updateBy、delFlag属性，只需要createTime,updateTime属性。

依赖引入

<dependencies>
        <!--mybatis-->
        <dependency>
            <groupId>com.baomidou</groupId>
            <artifactId>mybatis-plus-boot-starter</artifactId>
            <version>3.3.2</version>
        </dependency>
             <dependency>
            <groupId>org.projectlombok</groupId>
            <artifactId>lombok</artifactId>
            <version>1.18.12</version>
        </dependency>
    </dependencies>

公用实体类定义

package com.cloud.pango.common.core.entity;

import com.baomidou.mybatisplus.annotation.FieldFill;
import com.baomidou.mybatisplus.annotation.TableField;
import lombok.Data;
import lombok.EqualsAndHashCode;
import lombok.ToString;

import java.util.Date;

@Data
@ToString
@EqualsAndHashCode
public class BaseEntity{

    @TableField(fill = FieldFill.INSERT)//插入时填充
    private Date createTime;

    @TableField(fill = FieldFill.INSERT_UPDATE)//插入货更新时填充
    private Date updateTime;
}

package com.cloud.pango.common.core.entity;

import com.baomidou.mybatisplus.annotation.FieldFill;
import com.baomidou.mybatisplus.annotation.TableField;
import com.baomidou.mybatisplus.annotation.TableLogic;
import lombok.Data;
import lombok.EqualsAndHashCode;
import lombok.ToString;

@Data
@ToString
@EqualsAndHashCode
public class DefaultEntity extends BaseEntity{

    @TableField(fill = FieldFill.INSERT) //插入时填充
    private String createBy;

    @TableField(fill = FieldFill.INSERT_UPDATE)//插入或更新时填充
    private String updateBy;

    @TableField(fill = FieldFill.INSERT) //插入时填充
    @TableLogic//逻辑删除
    private Integer delFlag;
}

自动填充处理

package com.cloud.pango.common.mybatis;
import com.baomidou.mybatisplus.core.handlers.MetaObjectHandler;
import lombok.extern.slf4j.Slf4j;
import org.apache.ibatis.reflection.MetaObject;
import org.springframework.beans.factory.annotation.Autowired;
import java.util.Date;

@Slf4j
public class EntityMetaObjectHanlder implements MetaObjectHandler {

    private final static String CREATE_TIME = "createTime";

    private final static String UPDATE_TIME = "updateTime";

    private final static String CREATE_BY = "createBy";

    private final static String UPDATE_BY = "updateBy";

    private final static String DEL_FLAG = "delFlag";

    @Autowired
    private MetaObjectOperator metaObjectOperator;

    private void setMeta(MetaObject metaObject,String field,Object defaultValue){
        if(metaObject.hasGetter(field)){
            Object value = metaObject.getValue(field);
            if(null != value){
                this.setFieldValByName(field,value,metaObject);
            }else {
                this.setFieldValByName(field,defaultValue,metaObject);
            }
        }
    }

    private void setCreateTime(MetaObject metaObject){
        setMeta(metaObject,CREATE_TIME,new Date());
    }

    private void setUpdateTime(MetaObject metaObject){
        setMeta(metaObject,UPDATE_TIME,new Date());
    }

    private void setCreateBy(MetaObject metaObject){
        Object createBy = metaObjectOperator.getCreateBy();
        if(null == createBy){
            return ;
        }
        setMeta(metaObject,CREATE_BY,createBy);
    }

    private void setUpdateBy(MetaObject metaObject){
        Object updateBy = metaObjectOperator.getUpdateBy();
        if(null == updateBy){
            return ;
        }
        setMeta(metaObject,UPDATE_BY,updateBy);
    }

    private void setDelFlag(MetaObject metaObject){
        setMeta(metaObject,DEL_FLAG,0);
    }

    @Override
    public void insertFill(MetaObject metaObject) {
        String name = metaObject.getOriginalObject().getClass().getName();
        if(log.isDebugEnabled()){
            log.debug("{} 自动装配 createTime、updateTime、createBy、updateBy、delFlag",name);
        }
        setCreateTime(metaObject);
        setUpdateTime(metaObject);
        setCreateBy(metaObject);
        setUpdateBy(metaObject);
        setDelFlag(metaObject);
    }

    @Override
    public void updateFill(MetaObject metaObject) {
        String name = metaObject.getOriginalObject().getClass().getName();
        if(log.isDebugEnabled()){
            log.debug("{} 自动装配 updateTime、updateBy",name);
        }
        setUpdateTime(metaObject);
        setUpdateBy(metaObject);
    }
}

数据库读写分离

在分布式纵横的年代，人们想方设法提高应用程序的性能，将数据库拆分为读写分离模式【主从复制】是一项提供性能的一种方案。

当然这种方案只针对对数据一致性没那么高要求的程序【弱一致性】。因为在主数据库同步给从数据库时候有可能会出现一些额外情况，如网络原因等，导致主从数据库数据不一致。

本案例采用动态数据源及mybatis-plus来实现读写分离

引入依赖

        <dependencies>
        <!--mybatis-->
        <dependency>
            <groupId>com.baomidou</groupId>
            <artifactId>mybatis-plus-boot-starter</artifactId>
            <version>3.3.2</version>
        </dependency>
             <dependency>
            <groupId>org.projectlombok</groupId>
            <artifactId>lombok</artifactId>
            <version>1.18.12</version>
        </dependency>
      <dependency>
            <groupId>com.baomidou</groupId>
            <artifactId>dynamic-datasource-spring-boot-starter</artifactId>
            <version>3.1.1</version>
        </dependency>
    </dependencies>

配置application.yml文件

配置名为master的主数据库【用于写操作】及名为slave的从数据库【读操作】

spring:
  datasource:
    dynamic:
      druid: # 全局druid参数，绝大部分值和默认保持一致。(现已支持的参数如下,不清楚含义不要乱设置)
        # 连接池的配置信息
        # 初始化大小，最小，最大
        initial-size: 5
        min-idle: 5
        maxActive: 20
        # 配置获取连接等待超时的时间
        maxWait: 60000
        # 配置间隔多久才进行一次检测，检测需要关闭的空闲连接，单位是毫秒
        timeBetweenEvictionRunsMillis: 60000
        # 配置一个连接在池中最小生存的时间，单位是毫秒
        minEvictableIdleTimeMillis: 300000
        validationQuery: SELECT 1 FROM DUAL
        testWhileIdle: true
        testOnBorrow: false
        testOnReturn: false
        # 打开PSCache，并且指定每个连接上PSCache的大小
        poolPreparedStatements: true
        maxPoolPreparedStatementPerConnectionSize: 20
        # 配置监控统计拦截的filters，去掉后监控界面sql无法统计，‘wall‘用于防火墙
        filters: stat,wall,slf4j
        # 通过connectProperties属性来打开mergeSql功能；慢SQL记录
        connectionProperties: druid.stat.mergeSql=true;druid.stat.slowSqlMillis=5000
      datasource:
        master:
          url: ${mysql_URL:jdbc:mysql://localhost:3306/master?characterEncoding=UTF-8&useUnicode=true&useSSL=false}
          username: ${MYSQL_USER:root}
          password: ${MYSQL_PASS:123456}
          driver-class-name: com.mysql.cj.jdbc.Driver
        slave:
          url: ${MYSQL_URL:jdbc:mysql://localhost:3306/slave?characterEncoding=UTF-8&useUnicode=true&useSSL=false}
          username: ${MYSQL_USER:root}
          password: ${MYSQL_PASS:123456}
          driver-class-name: com.mysql.cj.jdbc.Driver

程序使用读写分离

• 显式使用

  只需在对应的方法上加上@DS注解并指明对应的数据源即可

  package com.cloud.pango.uc.service.impl;
  
  import com.baomidou.dynamic.datasource.annotation.DS;
  import com.baomidou.mybatisplus.extension.service.impl.ServiceImpl;
  import com.cloud.pango.uc.demo.DemoEntity;
  import com.cloud.pango.uc.mapper.DemoMapper;
  import com.cloud.pango.uc.service.DemoService;
  import org.springframework.stereotype.Service;
  import org.springframework.transaction.annotation.Transactional;
  
  @Service
  public class DemoServiceImpl extends ServiceImpl<DemoMapper, DemoEntity> implements DemoService {
  
    @DS("master")//标明使用master数据源
    @Override
    public Boolean insert(DemoEntity demo) {
        save(demo);
        return true;
    }
  
    @DS("slave")//标明使用slave数据源
    @Override
    public DemoEntity findById(String id){
        DemoEntity demo = getById(id);
        return demo;
    }
  
  }
  

• 隐式使用

  在未使用注解时，使用mybatis-plus拦截器，将读请求转移到slave数据源处理，将写请求转移到master数据源处理

package com.cloud.pango.uc.common;

import com.baomidou.dynamic.datasource.toolkit.DynamicDataSourceContextHolder;
import lombok.extern.slf4j.Slf4j;
import org.apache.commons.lang3.StringUtils;
import org.apache.ibatis.executor.Executor;
import org.apache.ibatis.mapping.MappedStatement;
import org.apache.ibatis.mapping.SqlCommandType;
import org.apache.ibatis.plugin.*;
import org.apache.ibatis.session.ResultHandler;
import org.apache.ibatis.session.RowBounds;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.stereotype.Component;
import org.springframework.transaction.support.TransactionSynchronizationManager;

import java.util.Properties;

@Intercepts({
        @Signature(type = Executor.class, method = "update", args = {
                MappedStatement.class, Object.class }),
        @Signature(type = Executor.class, method = "query", args = {
                MappedStatement.class, Object.class, RowBounds.class,
                ResultHandler.class }) })
@Slf4j
@Component
public class DynamicInterceptor implements Interceptor {

    private static final String MASTER = "master";

    private static final String SLAVE = "slave";

    @Override
    public Object intercept(Invocation invocation) throws Throwable {
        boolean synchronizationActive = TransactionSynchronizationManager.isSynchronizationActive();
        if(!synchronizationActive) {
            Object[] objects = invocation.getArgs();
            MappedStatement ms = (MappedStatement) objects[0];
            String currentDataSource = DynamicDataSourceContextHolder.peek();
            if(StringUtils.isEmpty(currentDataSource)){
                if(ms.getSqlCommandType().equals(SqlCommandType.SELECT)) {
                    DynamicDataSourceContextHolder.push(SLAVE);
                }else{
                    DynamicDataSourceContextHolder.push(MASTER);
                }
                Object proceed = invocation.proceed();
                DynamicDataSourceContextHolder.clear();
                return proceed;
            }
        }
        return invocation.proceed();
    }

    @Override
    public Object plugin(Object target) {
        if (target instanceof Executor) {
            return Plugin.wrap(target, this);
        } else {
            return target;
        }
    }

    @Override
    public void setProperties(Properties properties) {
    }
}