mysql|SpringBoot + MyBatis + MySQL 实现读写分离 boot|mysql|java|spring

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。

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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。

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实践 maven依赖

4.0.0com.cjs.example cjs-datasource-demo 0.0.1-SNAPSHOTjarcjs-datasource-demo org.springframework.boot spring-boot-starter-parent 2.0.5.RELEASE UTF-8UTF-8 1.8 org.springframework.boot spring-boot-starter-aop org.springframework.boot spring-boot-starter-jdbc org.springframework.boot spring-boot-starter-web org.mybatis.spring.boot mybatis-spring-boot-starter 1.3.2 org.apache.commons commons-lang3 3.8 mysql mysql-connector-java runtime org.springframework.boot spring-boot-starter-test test org.springframework.boot spring-boot-maven-plugin

数据源配置
application.yml

spring: datasource: master: jdbc-url: jdbc:mysql://192.168.102.31:3306/test username: root password: 123456 driver-class-name: com.mysql.jdbc.Driver slave1: jdbc-url: jdbc:mysql://192.168.102.56:3306/test username: pig# 只读账户 password: 123456 driver-class-name: com.mysql.jdbc.Driver slave2: jdbc-url: jdbc:mysql://192.168.102.36:3306/test username: pig# 只读账户 password: 123456 driver-class-name: com.mysql.jdbc.Driver

多数据源配置

package com.cjs.example.config; import com.cjs.example.bean.MyRoutingDataSource; import com.cjs.example.enums.DBTypeEnum; import org.springframework.beans.factory.annotation.Qualifier; import org.springframework.boot.context.properties.ConfigurationProperties; import org.springframework.boot.jdbc.DataSourceBuilder; import org.springframework.context.annotation.Bean; import org.springframework.context.annotation.Configuration; import javax.sql.DataSource; import java.util.HashMap; import java.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 */@Configuration public class DataSourceConfig {@Bean @ConfigurationProperties("spring.datasource.master") public DataSource masterDataSource() { return DataSourceBuilder.create().build(); }@Bean @ConfigurationProperties("spring.datasource.slave1") public DataSource slave1DataSource() { return DataSourceBuilder.create().build(); }@Bean @ConfigurationProperties("spring.datasource.slave2") public DataSource slave2DataSource() { return DataSourceBuilder.create().build(); }@Bean public DataSource myRoutingDataSource(@Qualifier("masterDataSource") DataSource masterDataSource, @Qualifier("slave1DataSource") DataSource slave1DataSource, @Qualifier("slave2DataSource") DataSource slave2DataSource) { Map 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); return myRoutingDataSource; }}

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

package com.cjs.example.config; import org.apache.ibatis.session.SqlSessionFactory; import org.mybatis.spring.SqlSessionFactoryBean; import org.springframework.context.annotation.Bean; import org.springframework.context.annotation.Configuration; import org.springframework.core.io.support.PathMatchingResourcePatternResolver; import org.springframework.jdbc.datasource.DataSourceTransactionManager; import org.springframework.transaction.PlatformTransactionManager; import org.springframework.transaction.annotation.EnableTransactionManagement; import javax.annotation.Resource; import javax.sql.DataSource; @EnableTransactionManagement @Configuration public class MyBatisConfig {@Resource(name = "myRoutingDataSource") private DataSource myRoutingDataSource; @Bean public SqlSessionFactory sqlSessionFactory() throws Exception { SqlSessionFactoryBean sqlSessionFactoryBean = new SqlSessionFactoryBean(); sqlSessionFactoryBean.setDataSource(myRoutingDataSource); sqlSessionFactoryBean.setMapperLocations(new PathMatchingResourcePatternResolver().getResources("classpath:mapper/*.xml")); return sqlSessionFactoryBean.getObject(); }@Bean public PlatformTransactionManager platformTransactionManager() { return new 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。
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

package com.cjs.example.enums; public enum DBTypeEnum {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; public class DBContextHolder {private static final ThreadLocal contextHolder = new ThreadLocal<>(); private static final AtomicInteger counter = new AtomicInteger(-1); public static void set(DBTypeEnum dbType) { contextHolder.set(dbType); }public static DBTypeEnum get() { return contextHolder.get(); }public static void master() { set(DBTypeEnum.MASTER); System.out.println("切换到master"); }public static void slave() { //轮询 int index = 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

package com.cjs.example.bean; import org.springframework.jdbc.datasource.lookup.AbstractRoutingDataSource; import org.springframework.lang.Nullable; public class MyRoutingDataSource extends AbstractRoutingDataSource { @Nullable @Override protected Object determineCurrentLookupKey() { return DBContextHolder.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）

package com.cjs.example.aop; import com.cjs.example.bean.DBContextHolder; import org.apache.commons.lang3.StringUtils; import org.aspectj.lang.JoinPoint; import org.aspectj.lang.annotation.Aspect; import org.aspectj.lang.annotation.Before; import org.aspectj.lang.annotation.Pointcut; import org.springframework.stereotype.Component; @Aspect @Component public class DataSourceAop {@Pointcut("!@annotation(com.cjs.example.annotation.Master) " + "&& (execution(* com.cjs.example.service..*.select*(..)) " + "|| execution(* com.cjs.example.service..*.get*(..)))") public void readPointcut() {}@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*(..))") public void writePointcut() {}@Before("readPointcut()") public void read() { DBContextHolder.slave(); }@Before("writePointcut()") public void write() { 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(); //} //} }

【mysql|SpringBoot + MyBatis + MySQL 实现读写分离】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

package com.cjs.example.annotation; public @interface Master { }

例如，假设我们有一张表member

package com.cjs.example.service.impl; import com.cjs.example.annotation.Master; import com.cjs.example.entity.Member; import com.cjs.example.entity.MemberExample; import com.cjs.example.mapper.MemberMapper; import com.cjs.example.service.MemberService; import org.springframework.beans.factory.annotation.Autowired; import org.springframework.stereotype.Service; import org.springframework.transaction.annotation.Transactional; import java.util.List; @Service public class MemberServiceImpl implements MemberService {@Autowired private MemberMapper memberMapper; @Transactional @Override public int insert(Member member) { return memberMapper.insert(member); }@Master @Override public int save(Member member) { return memberMapper.insert(member); }@Override public List selectAll() { return memberMapper.selectByExample(new MemberExample()); }@Master @Override public String getToken(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 return null; } }

测试

package com.cjs.example; import com.cjs.example.entity.Member; import com.cjs.example.service.MemberService; import org.junit.Test; import org.junit.runner.RunWith; import org.springframework.beans.factory.annotation.Autowired; import org.springframework.boot.test.context.SpringBootTest; import org.springframework.test.context.junit4.SpringRunner; @RunWith(SpringRunner.class) @SpringBootTest public class CjsDatasourceDemoApplicationTests {@Autowired private MemberService memberService; @Test public void testWrite() { Member member = new Member(); member.setName("zhangsan"); memberService.insert(member); }@Test public void testRead() { for (int i = 0; i < 4; i++) { memberService.selectAll(); } }@Test public void testSave() { Member member = new Member(); member.setName("wangwu"); memberService.save(member); }@Test public void testReadFromMaster() { memberService.getToken("1234"); }}

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