SpringBoot+MyBatis+MySQL读写分离

maven依赖

4.0.0

com.cjs.example
cjs-datasource-demo
0.0.1-SNAPSHOT
jar

cjs-datasource-demo



    org.springframework.boot
    spring-boot-starter-parent
    2.0.5.RELEASE
     



    UTF-8
    UTF-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
        
    

3.2. 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

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;

}
复制代码接下来，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。

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();
}

}
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");
}

}