SpringBoot+MyBatis+MySQL读写分离实战

1 引言

读写分离要做的事情就是对于一条SQL该选择哪个数据库去执行，至于谁来做选择数据库这件事儿，无非两个，要么中间件帮我们做，要么程序自己做。因此，一般来讲，读写分离有两种实现方式。第一种是依靠中间件（比如：MyCat），也就是说应用程序连接到中间件，中间件帮我们做SQL分离；第二种是应用程序自己去做分离。这里我们选择程序自己来做，主要是利用Spring提供的路由数据源，以及AOP

然而，应用程序层面去做读写分离最大的弱点（不足之处）在于无法动态增加数据库节点，因为数据源配置都是写在配置中的，新增数据库意味着新加一个数据源，必然改配置，并重启应用。当然，好处就是相对简单。

2 AbstractRoutingDataSource

基于特定的查找key路由到特定的数据源。它内部维护了一组目标数据源，并且做了路由key与目标数据源之间的映射，提供基于key查找数据源的方法。

3 实践

关于配置请参考：

https://www.cnblogs.com/cjsblog/p/9706370.html

3.1 maven依赖

<?xml version="1.0" encoding="UTF-8"?>4.0.0com.cjs.examplecjs-datasource-demo0.0.1-SNAPSHOTjarcjs-datasource-demoorg.springframework.bootspring-boot-starter-parent2.0.5.RELEASE<!-- lookup parent from repository -->UTF-8UTF-81.8org.springframework.bootspring-boot-starter-aoporg.springframework.bootspring-boot-starter-jdbcorg.springframework.bootspring-boot-starter-weborg.mybatis.spring.bootmybatis-spring-boot-starter1.3.2org.apache.commonscommons-lang33.8mysqlmysql-connector-javaruntimeorg.springframework.bootspring-boot-starter-testtestorg.springframework.bootspring-boot-maven-plugin<!--<plugin><groupId>org.mybatis.generator</groupId><artifactId>mybatis-generator-maven-plugin</artifactId><version>1.3.5</version><dependencies><dependency><groupId>mysql</groupId><artifactId>mysql-connector-java</artifactId><version>5.1.46</version></dependency></dependencies><configuration><configurationFile>${basedir}/src/main/resources/myBatisGeneratorConfig.xml</configurationFile><overwrite>true</overwrite></configuration><executions><execution><id>Generate MyBatis Artifacts</id><goals><goal>generate</goal></goals></execution></executions></plugin>-->

3.2 数据源配置

application.yml

spring:datasource:master:jdbc-url: jdbc:mysql://192.168.102.31:3306/testusername: rootpassword: 123456driver-class-name: com.mysql.jdbc.Driverslave1:jdbc-url: jdbc:mysql://192.168.102.56:3306/testusername: pig # 只读账户password: 123456driver-class-name: com.mysql.jdbc.Driverslave2:jdbc-url: jdbc:mysql://192.168.102.36:3306/testusername: pig # 只读账户password: 123456driver-class-name: com.mysql.jdbc.Driver

多数据源配置

packagecom.cjs.example.config;importcom.cjs.example.bean.MyRoutingDataSource;importcom.cjs.example.enums.DBTypeEnum;importorg.springframework.beans.factory.annotation.Qualifier;importorg.springframework.boot.context.properties.ConfigurationProperties;importorg.springframework.boot.jdbc.DataSourceBuilder;importorg.springframework.context.annotation.Bean;importorg.springframework.context.annotation.Configuration;importjavax.sql.DataSource;importjava.util.HashMap;importjava.util.Map;/*** 关于数据源配置，参考SpringBoot官方文档第79章《Data Access》* 79. Data Access* 79.1 Configure a Custom DataSource* 79.2 Configure Two DataSources*/@ConfigurationpublicclassDataSourceConfig{@Bean@ConfigurationProperties("spring.datasource.master")publicDataSource masterDataSource() {returnDataSourceBuilder.create().build();}@Bean@ConfigurationProperties("spring.datasource.slave1")publicDataSource slave1DataSource() {returnDataSourceBuilder.create().build();}@Bean@ConfigurationProperties("spring.datasource.slave2")publicDataSource slave2DataSource() {returnDataSourceBuilder.create().build();}@BeanpublicDataSource myRoutingDataSource(@Qualifier("masterDataSource")DataSource masterDataSource,@Qualifier("slave1DataSource")DataSource slave1DataSource,@Qualifier("slave2DataSource")DataSource slave2DataSource) {Map<Object, Object> targetDataSources = new HashMap<>();targetDataSources.put(DBTypeEnum.MASTER, masterDataSource);targetDataSources.put(DBTypeEnum.SLAVE1, slave1DataSource);targetDataSources.put(DBTypeEnum.SLAVE2, slave2DataSource);MyRoutingDataSource myRoutingDataSource = new MyRoutingDataSource();myRoutingDataSource.setDefaultTargetDataSource(masterDataSource);myRoutingDataSource.setTargetDataSources(targetDataSources);returnmyRoutingDataSource;}}

这里，我们配置了4个数据源，1个master，2两个slave，1个路由数据源。前3个数据源都是为了生成第4个数据源，而且后续我们只用这最后一个路由数据源。

MyBatis配置

packagecom.cjs.example.config;importorg.apache.ibatis.session.SqlSessionFactory;importorg.mybatis.spring.SqlSessionFactoryBean;importorg.springframework.context.annotation.Bean;importorg.springframework.context.annotation.Configuration;importorg.springframework.core.io.support.PathMatchingResourcePatternResolver;importorg.springframework.jdbc.datasource.DataSourceTransactionManager;importorg.springframework.transaction.PlatformTransactionManager;importorg.springframework.transaction.annotation.EnableTransactionManagement;importjavax.annotation.Resource;importjavax.sql.DataSource;@EnableTransactionManagement@ConfigurationpublicclassMyBatisConfig{@Resource(name ="myRoutingDataSource")privateDataSource myRoutingDataSource;@BeanpublicSqlSessionFactory sqlSessionFactory() throws Exception {SqlSessionFactoryBean sqlSessionFactoryBean = new SqlSessionFactoryBean();sqlSessionFactoryBean.setDataSource(myRoutingDataSource);sqlSessionFactoryBean.setMapperLocations(new PathMatchingResourcePatternResolver().getResources("classpath:mapper/*.xml"));returnsqlSessionFactoryBean.getObject();}@BeanpublicPlatformTransactionManager platformTransactionManager() {returnnew DataSourceTransactionManager(myRoutingDataSource);}}

由于Spring容器中现在有4个数据源，所以我们需要为事务管理器和MyBatis手动指定一个明确的数据源。

3.3 设置路由key / 查找数据源

目标数据源就是那前3个这个我们是知道的，但是使用的时候是如果查找数据源的呢？ 首先，我们定义一个枚举来代表这三个数据源

packagecom.cjs.example.enums;publicenumDBTypeEnum {MASTER, SLAVE1, SLAVE2;}

接下来，通过ThreadLocal将数据源设置到每个线程上下文中

package com.cjs.example.bean;import com.cjs.example.enums.DBTypeEnum;import java.util.concurrent.atomic.AtomicInteger;publicclassDBContextHolder{privatestaticfinal ThreadLocal contextHolder =newThreadLocal<>();privatestaticfinal AtomicInteger counter =newAtomicInteger(-1);publicstaticvoidset(DBTypeEnum dbType){contextHolder.set(dbType);}publicstaticDBTypeEnumget(){returncontextHolder.get();}publicstaticvoidmaster(){set(DBTypeEnum.MASTER);System.out.println("切换到master");}publicstaticvoidslave(){// 轮询intindex = counter.getAndIncrement() %2;if(counter.get() >9999) {counter.set(-1);}if(index ==0) {set(DBTypeEnum.SLAVE1);System.out.println("切换到slave1");}else{set(DBTypeEnum.SLAVE2);System.out.println("切换到slave2");}}}

获取路由key

packagecom.cjs.example.bean;importorg.springframework.jdbc.datasource.lookup.AbstractRoutingDataSource;importorg.springframework.lang.Nullable;publicclassMyRoutingDataSourceextendsAbstractRoutingDataSource{@Nullable@OverrideprotectedObjectdetermineCurrentLookupKey(){returnDBContextHolder.get();}}

设置路由key

默认情况下，所有的查询都走从库，插入/修改/删除走主库。我们通过方法名来区分操作类型（CRUD）

packagecom.cjs.example.aop;importcom.cjs.example.bean.DBContextHolder;importorg.apache.commons.lang3.StringUtils;importorg.aspectj.lang.JoinPoint;importorg.aspectj.lang.annotation.Aspect;importorg.aspectj.lang.annotation.Before;importorg.aspectj.lang.annotation.Pointcut;importorg.springframework.stereotype.Component;@Aspect@ComponentpublicclassDataSourceAop{@Pointcut("!@annotation(com.cjs.example.annotation.Master) "+"&& (execution(* com.cjs.example.service..*.select*(..)) "+"|| execution(* com.cjs.example.service..*.get*(..)))")publicvoidreadPointcut(){}@Pointcut("@annotation(com.cjs.example.annotation.Master) "+"|| execution(* com.cjs.example.service..*.insert*(..)) "+"|| execution(* com.cjs.example.service..*.add*(..)) "+"|| execution(* com.cjs.example.service..*.update*(..)) "+"|| execution(* com.cjs.example.service..*.edit*(..)) "+"|| execution(* com.cjs.example.service..*.delete*(..)) "+"|| execution(* com.cjs.example.service..*.remove*(..))")publicvoidwritePointcut(){}@Before("readPointcut()")publicvoidread(){DBContextHolder.slave();}@Before("writePointcut()")publicvoidwrite(){DBContextHolder.master();}/*** 另一种写法：if...else... 判断哪些需要读从数据库，其余的走主数据库*/// @Before("execution(* com.cjs.example.service.impl.*.*(..))")// public void before(JoinPoint jp) {// String methodName = jp.getSignature().getName();//// if (StringUtils.startsWithAny(methodName, "get", "select", "find")) {// DBContextHolder.slave();// }else {// DBContextHolder.master();// }// }}

有一般情况就有特殊情况，特殊情况是某些情况下我们需要强制读主库，针对这种情况，我们定义一个主键，用该注解标注的就读主库。

packagecom.cjs.example.annotation;public@interfaceMaster {}

例如，假设我们有一张表member

packagecom.cjs.example.service.impl;importcom.cjs.example.annotation.Master;importcom.cjs.example.entity.Member;importcom.cjs.example.entity.MemberExample;importcom.cjs.example.mapper.MemberMapper;importcom.cjs.example.service.MemberService;importorg.springframework.beans.factory.annotation.Autowired;importorg.springframework.stereotype.Service;importorg.springframework.transaction.annotation.Transactional;importjava.util.List;@ServicepublicclassMemberServiceImplimplementsMemberService{@AutowiredprivateMemberMapper memberMapper;@Transactional@Overridepublicintinsert(Member member){returnmemberMapper.insert(member);}@Master@Overridepublicintsave(Member member){returnmemberMapper.insert(member);}@OverridepublicListselectAll(){returnmemberMapper.selectByExample(newMemberExample());}@Master@OverridepublicStringgetToken(String appId){// 有些读操作必须读主数据库// 比如，获取微信access_token，因为高峰时期主从同步可能延迟// 这种情况下就必须强制从主数据读returnnull;}}

4 测试

测试

packagecom.cjs.example;importcom.cjs.example.entity.Member;importcom.cjs.example.service.MemberService;importorg.junit.Test;importorg.junit.runner.RunWith;importorg.springframework.beans.factory.annotation.Autowired;importorg.springframework.boot.test.context.SpringBootTest;importorg.springframework.test.context.junit4.SpringRunner;@RunWith(SpringRunner.class)@SpringBootTestpublicclassCjsDatasourceDemoApplicationTests{@AutowiredprivateMemberService memberService;@TestpublicvoidtestWrite(){Member member =newMember();member.setName("zhangsan");memberService.insert(member);}@TestpublicvoidtestRead(){for(inti =0; i <4; i++) {memberService.selectAll();}}@TestpublicvoidtestSave(){Member member =newMember();member.setName("wangwu");memberService.save(member);}@TestpublicvoidtestReadFromMaster(){memberService.getToken("1234");}}

查看控制台

5 工程结构

6 参考

https://www.jianshu.com/p/f2f4256a2310http://www.cnblogs.com/gl-developer/p/6170423.htmlhttps://www.cnblogs.com/huangjuncong/p/8576935.htmlhttps://blog.csdn.net/liu976180578/article/details/77684583

https://mp.weixin.qq.com/s/KvLKqNPacRRmAFjzdQ2p6Q