Spring Boot + MyBatis + MySQL 实现读写分离

秒速五厘米 2022-09-11 00:17 140阅读 0赞

作者：废物大师兄  
来源：[https://www.cnblogs.com/cjsblog/p/9712457.html][https_www.cnblogs.com_cjsblog_p_9712457.html]

## 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。

![20210910091331666.png][]

## 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。

![2021091009133285.png][]

## 3、实践 ##

#### 3.1. maven依赖 ####

<?xml version="1.0" encoding="UTF-8"?>
    <project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
        xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
        <modelVersion>4.0.0</modelVersion>
    
        <groupId>com.cjs.example</groupId>
        <artifactId>cjs-datasource-demo</artifactId>
        <version>0.0.1-SNAPSHOT</version>
        <packaging>jar</packaging>
    
        <name>cjs-datasource-demo</name>
        <description></description>
    
        <parent>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-parent</artifactId>
            <version>2.0.5.RELEASE</version>
            <relativePath/> 
        </parent>
    
        <properties>
            <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
            <project.reporting.outputEncoding>UTF-8</project.reporting.outputEncoding>
            <java.version>1.8</java.version>
        </properties>
    
        <dependencies>
            <dependency>
                <groupId>org.springframework.boot</groupId>
                <artifactId>spring-boot-starter-aop</artifactId>
            </dependency>
            <dependency>
                <groupId>org.springframework.boot</groupId>
                <artifactId>spring-boot-starter-jdbc</artifactId>
            </dependency>
            <dependency>
                <groupId>org.springframework.boot</groupId>
                <artifactId>spring-boot-starter-web</artifactId>
            </dependency>
            <dependency>
                <groupId>org.mybatis.spring.boot</groupId>
                <artifactId>mybatis-spring-boot-starter</artifactId>
                <version>1.3.2</version>
            </dependency>
            <dependency>
                <groupId>org.apache.commons</groupId>
                <artifactId>commons-lang3</artifactId>
                <version>3.8</version>
            </dependency>
    
            <dependency>
                <groupId>mysql</groupId>
                <artifactId>mysql-connector-java</artifactId>
                <scope>runtime</scope>
            </dependency>
            <dependency>
                <groupId>org.springframework.boot</groupId>
                <artifactId>spring-boot-starter-test</artifactId>
                <scope>test</scope>
            </dependency>
        </dependencies>
    
        <build>
            <plugins>
                <plugin>
                    <groupId>org.springframework.boot</groupId>
                    <artifactId>spring-boot-maven-plugin</artifactId>
                </plugin>
    
    
                
    
            </plugins>
        </build>
    </project>

#### 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<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);
            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。

#### 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

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<DBTypeEnum> 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();
    //        }
    //    }
    }

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<Member> 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;
        }
    }

## 4、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");
        }
    
    }

查看控制台

![20210910091332476.png][]

![20210910091332883.png][]

![20210910091333241.png][]

![img][]

## 5、工程结构 ##

![20210910091334281.png][]

参考：

[https://www.jianshu.com/p/f2f4256a2310][https_www.jianshu.com_p_f2f4256a2310]  
[http://www.cnblogs.com/gl-developer/p/6170423.html][http_www.cnblogs.com_gl-developer_p_6170423.html]  
[https://www.cnblogs.com/huangjuncong/p/8576935.html][https_www.cnblogs.com_huangjuncong_p_8576935.html]  
[https://blog.csdn.net/liu976180578/article/details/77684583][https_blog.csdn.net_liu976180578_article_details_77684583]

**近期热文推荐：**

1.[1,000+ 道 Java面试题及答案整理(2021最新版)][1_000_ _ Java_2021]

2.[别在再满屏的 if/ else 了，试试策略模式，真香！！][if_ else]

3.[卧槽！Java 中的 xx ≠ null 是什么新语法？][Java _ xx _ null]

4.[Spring Boot 2.5 重磅发布，黑暗模式太炸了！][Spring Boot 2.5]

5.[《Java开发手册（嵩山版）》最新发布，速速下载！][Java]

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[https_www.cnblogs.com_cjsblog_p_9712457.html]: https://www.cnblogs.com/cjsblog/p/9712457.html
[20210910091331666.png]: /images/20220829/58a8e048a70c42ec9241a7006f92183b.png
[2021091009133285.png]: /images/20220829/bc4cdd37be70422c80f44293ab3e9d4f.png
[20210910091332476.png]: /images/20220829/e839a0e5ab0948ccb631973760aedfe1.png
[20210910091332883.png]: /images/20220829/4513b6a0d2c844d09d6347cafe421dae.png
[20210910091333241.png]: /images/20220829/b235236f75d8431a91f13ea4102179af.png
[img]: /images/20220829/00a1ebd59cf240c7aa2ada55e8c699c9.png
[20210910091334281.png]: /images/20220829/d6d9e46f099341f2afeafd062a6120c1.png
[https_www.jianshu.com_p_f2f4256a2310]: https://www.jianshu.com/p/f2f4256a2310
[http_www.cnblogs.com_gl-developer_p_6170423.html]: http://www.cnblogs.com/gl-developer/p/6170423.html
[https_www.cnblogs.com_huangjuncong_p_8576935.html]: https://www.cnblogs.com/huangjuncong/p/8576935.html
[https_blog.csdn.net_liu976180578_article_details_77684583]: https://blog.csdn.net/liu976180578/article/details/77684583
[1_000_ _ Java_2021]: https://www.javastack.cn/mst/
[if_ else]: https://www.javastack.cn/article/2021/strategy-pattern-instead-of-if-else/
[Java _ xx _ null]: https://www.javastack.cn/article/2021/intellij-idea-ligatures-settings/
[Spring Boot 2.5]: https://www.javastack.cn/article/2021/spring-boot-2.5-released/
[Java]: http://www.javastack.cn/article/2020/alibaba-release-java-develop-rules-songshan/