
CREATE TABLE `user` (
  `user_id` varchar(16) NOT NULL,
  `user_name` varchar(64) DEFAULT NULL,
  PRIMARY KEY (`user_id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COMMENT='user';
 
INSERT INTO `maple_master`.`user`(`user_id`, `user_name`) VALUES ('1', 'maple_master');
INSERT INTO `maple_slave`.`user`(`user_id`, `user_name`) VALUES ('1', 'maple_slave');

2、我这里使用常规的技术栈：SpingBoot + Mybatis + Maven，首先导入pom和基本编码


<?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 https://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>
    <parent>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-parent</artifactId>
        <version>2.4.3</version>
        <relativePath/> <!-- lookup parent from repository -->
    </parent>
    <groupId>com.gane.maple</groupId>
    <artifactId>read-write-separation-mybatisplus</artifactId>
    <version>0.0.1-SNAPSHOT</version>
    <name>read-write-separation-mybatis</name>
    <description>Demo project for Spring Boot</description>
    <properties>
        <java.version>1.8</java.version>
    </properties>
    <dependencies>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter</artifactId>
        </dependency>
 
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-web</artifactId>
        </dependency>
 
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-aop</artifactId>
            <version>2.4.2</version>
        </dependency>
 
        <dependency>
            <groupId>mysql</groupId>
            <artifactId>mysql-connector-java</artifactId>
            <scope>runtime</scope>
        </dependency>
        <dependency>
            <groupId>com.alibaba</groupId>
            <artifactId>druid-spring-boot-starter</artifactId>
            <version>1.1.10</version>
        </dependency>
        <dependency>
            <groupId>org.springframework</groupId>
            <artifactId>spring-jdbc</artifactId>
        </dependency>
 
        <dependency>
            <groupId>org.mybatis.spring.boot</groupId>
            <artifactId>mybatis-spring-boot-starter</artifactId>
            <version>2.1.3</version>
        </dependency>
 
        <dependency>
            <groupId>org.apache.commons</groupId>
            <artifactId>commons-lang3</artifactId>
            <version>3.9</version>
        </dependency>
 
        <dependency>
            <groupId>org.projectlombok</groupId>
            <artifactId>lombok</artifactId>
            <optional>true</optional>
        </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>

编码

1、多数据源配置文件


#master
spring.datasource.master.type=com.alibaba.druid.pool.DruidDataSource
spring.datasource.master.driver-class-name=com.mysql.cj.jdbc.Driver
spring.datasource.master.jdbc-url=jdbc:mysql://localhost:3306/maple_master?useUnicode=true&characterEncoding=UTF-8&serverTimezone=Asia/Shanghai&zeroDateTimeBehavior=convertToNull
spring.datasource.master.username=root
spring.datasource.master.password=root
 
#slave
spring.datasource.slave.type=com.alibaba.druid.pool.DruidDataSource
spring.datasource.slave.driver-class-name=com.mysql.cj.jdbc.Driver
spring.datasource.slave.jdbc-url=jdbc:mysql://localhost:3306/maple_slave?useUnicode=true&characterEncoding=UTF-8&serverTimezone=Asia/Shanghai&zeroDateTimeBehavior=convertToNull
spring.datasource.slave.username=root
spring.datasource.slave.password=root

2、DataSource配置


package com.gane.maple.jdbc.datasource;
 
import com.gane.maple.jdbc.routing.ClientDataSource;
import com.gane.maple.jdbc.routing.component.ClientDataSourceRouter;
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 org.springframework.context.annotation.Primary;
 
import javax.sql.DataSource;
import java.util.HashMap;
import java.util.Map;
 
/**
 * @author maple
 * @date 2021/3/3
 */
@Configuration
public class DataSourceConfig {
 
    @Bean(name = "masterDataSource")
    @ConfigurationProperties(prefix = "spring.datasource.master")
    public DataSource masterDataSource() {
        return DataSourceBuilder.create().build();
    }
 
    @Bean(name = "slaveDataSource")
    @ConfigurationProperties(prefix = "spring.datasource.slave")
    public DataSource slaveDataSource() {
        return DataSourceBuilder.create().build();
    }
 
    @Primary
    @Bean(name = "dynamicDatasource")
    public ClientDataSourceRouter dynamicDatasource(@Qualifier("masterDataSource") DataSource masterDataSource,
                                                    @Qualifier("slaveDataSource") DataSource slaveDataSource) {
 
        ClientDataSourceRouter dataSourceRouter = new ClientDataSourceRouter();
        dataSourceRouter.setDefaultTargetDataSource(masterDataSource);
 
        Map<Object, Object> targetDataSources = new HashMap<>();
        targetDataSources.put(ClientDataSource.MASTER, masterDataSource);
        targetDataSources.put(ClientDataSource.SLAVE, slaveDataSource);
        dataSourceRouter.setTargetDataSources(targetDataSources);
 
        return dataSourceRouter;
    }
}

3、MybatisConfig配置


package com.gane.maple.jdbc.datasource;
 
import org.apache.ibatis.session.SqlSessionFactory;
import org.mybatis.spring.SqlSessionFactoryBean;
import org.mybatis.spring.annotation.MapperScan;
import org.springframework.beans.factory.annotation.Qualifier;
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 javax.sql.DataSource;
 
/**
 * @author maple
 * @date 2021/3/3
 */
@Configuration
@MapperScan(MybatisConfig.MAPPER_PACKAGE)
public class MybatisConfig {
 
    public static final String MAPPER_PACKAGE = "com.gane.maple.dao";
    public static final String TYPE_ALIASES_PACKAGE = "com.gane.maple.dao.entity";
    public static final String MAPPER_XML_LOCATIONS = "mapper/*Mapper.xml";
 
    @Bean
    public SqlSessionFactory sqlSessionFactory(@Qualifier("dynamicDatasource") DataSource dataSource) throws Exception {
        SqlSessionFactoryBean factoryBean = new SqlSessionFactoryBean();
        factoryBean.setDataSource(dataSource);
        factoryBean.setTypeAliasesPackage(TYPE_ALIASES_PACKAGE);
        factoryBean.setMapperLocations(new PathMatchingResourcePatternResolver().getResources(MAPPER_XML_LOCATIONS));
        return factoryBean.getObject();
    }
 
    @Bean
    public DataSourceTransactionManager transactionManager(@Qualifier("dynamicDatasource") DataSource dataSource) {
        return new DataSourceTransactionManager(dataSource);
    }
}

4、创建 ClientDataSource 枚举定义主从库


package com.gane.maple.jdbc.routing;
 
/**
 * @author maple
 * @date 2021/3/3
 */
public enum ClientDataSource {
    MASTER, SLAVE
}

5、创建 ClientDataSourceContextHolder 来保存 ClientDataSource


package com.gane.maple.jdbc.routing;
 
import java.util.Objects;
 
/**
 * Context Holder that will hold the value for datasource routing for each different thread 
 * (request).
 *
 * @author maple
 * @date 2021/3/3
 */
public class ClientDataSourceContextHolder {
 
    private static final ThreadLocal<ClientDataSource> CONTEXT = new ThreadLocal<>();
 
    public static void set(ClientDataSource clientDataSource) {
        CONTEXT.set(Objects.requireNonNull(clientDataSource, "clientDatabase cannot be null"));
    }
 
    public static ClientDataSource getClientDatabase() {
        return CONTEXT.get();
    }
 
    public static void clear() {
        CONTEXT.remove();
    }
}

6、继承 AbstractRoutingDataSource

重写 determineCurrentLookupKey 方法，返回所使用的数据源的Key(master/slave)给到 resolvedDataSources，从而通过Key从resolvedDataSources里拿到其对应的DataSource


package com.gane.maple.jdbc.routing.component;
 
import com.gane.maple.jdbc.routing.ClientDataSource;
import com.gane.maple.jdbc.routing.ClientDataSourceContextHolder;
import lombok.extern.slf4j.Slf4j;
import org.springframework.jdbc.datasource.lookup.AbstractRoutingDataSource;
 
/**
 * {@link javax.sql.DataSource} for spring framework that will gives the desired     
 * datasource based on the
 * current value stored in the {@link ClientDataSourceContextHolder}
 *
 * @author maple
 * @date 2021/3/3
 */
@Slf4j
public class ClientDataSourceRouter extends AbstractRoutingDataSource {
 
    @Override
    protected Object determineCurrentLookupKey() {
        ClientDataSource clientDataSource = ClientDataSourceContextHolder.getClientDatabase();
        if (clientDataSource == null) {
            log.debug("null client database, use default {}", ClientDataSource.MASTER);
            clientDataSource = ClientDataSource.MASTER;
        }
        log.trace("use {} as database", clientDataSource);
        return clientDataSource;
    }
}

7、通过注解 DataSourceRouting 来标识走master/slave


package com.gane.maple.jdbc.routing.annotation;
 
import com.gane.maple.jdbc.routing.ClientDataSource;
 
import java.lang.annotation.ElementType;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;
 
/**
 * Indicates that a method uses a specific datasource defined in {@link ClientDataSource}.
 *
 * @author maple
 * @date 2021/3/3
 */
@Target(ElementType.METHOD)
@Retention(RetentionPolicy.RUNTIME)
public @interface DataSourceRouting {
 
    ClientDataSource value() default ClientDataSource.MASTER;
}

8、创建 DataSourceRoutingAspect，来处理注解 DataSourceRouting


package com.gane.maple.jdbc.routing.component;
 
import com.gane.maple.jdbc.routing.ClientDataSource;
import com.gane.maple.jdbc.routing.ClientDataSourceContextHolder;
import com.gane.maple.jdbc.routing.annotation.DataSourceRouting;
import lombok.extern.slf4j.Slf4j;
import org.aspectj.lang.ProceedingJoinPoint;
import org.aspectj.lang.annotation.Around;
import org.aspectj.lang.annotation.Aspect;
import org.springframework.stereotype.Component;
 
/**
 * Aspect that will mark a method to route to the desired datasource before calling the 
 * method.
 *
 * @author maple
 * @date 2021/3/3
 */
@Aspect
@Component
@Slf4j
public class DataSourceRoutingAspect {
 
    @Around("@annotation(dataSourceRouting)")
    public Object aroundDataSourceRouting(ProceedingJoinPoint joinPoint, DataSourceRouting dataSourceRouting)
            throws Throwable {
        ClientDataSource previousClient = ClientDataSourceContextHolder.getClientDatabase();
        log.warn("Setting clientDatabase {} into DataSourceContext", dataSourceRouting.value());
        ClientDataSourceContextHolder.set(dataSourceRouting.value());
 
        try {
            return joinPoint.proceed();
        } finally {
            if (previousClient != null) {
                // revert context back to previous state after execute the method
                ClientDataSourceContextHolder.set(previousClient);
            } else {
                // there is no value being set into the context before, just clear the context
                // to prevent memory leak
                ClientDataSourceContextHolder.clear();
            }
        }
    }
}

9、主类 ReadWriteSeparationMybatisApplication

由于我们没有使用 spring.datasource.url、spring.datasource.username 默认的配置，而是自定义的 spring.datasource.master.jdbc-url、spring.datasource.master.username 等配置，

所以我们需要排除Spring的自动配置类 DataSourceAutoConfiguration，防止在我们启动项目的时候，由于找不到 spring.datasource.url、spring.datasource.username 等配置而报了 “url” 未配置的错误。


package com.gane.maple;
 
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.boot.autoconfigure.jdbc.DataSourceAutoConfiguration;
 
@SpringBootApplication(exclude = {DataSourceAutoConfiguration.class})
public class ReadWriteSeparationMybatisApplication {
 
    public static void main(String[] args) {
        SpringApplication.run(ReadWriteSeparationMybatisApplication.class, args);
    }
}

10、测试

自测成功，可自行debug

TestController：


package com.gane.maple.controller;
 
import com.gane.maple.entity.User;
import com.gane.maple.service.UserService;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RestController;
 
/**
 * @author maple
 * @date 2021/3/2
 */
@RestController
public class TestController {
 
    @Autowired
    private UserService userService;
 
    @GetMapping("/queryUser")
    public User queryUser() {
 
        User userFromMaster = userService.selectByUserId("1");
 
        User userFromSlave = userService.selectByUserName("maple_slave");
 
        User userFromMasterAndSlave = userService.selectFromMasterAndSlave("1", "maple_slave");
 
        User selectFromMasterAndSlaveWithDataSourceRouting = userService.selectFromMasterAndSlaveWithDataSourceRoutingInDao("1", "maple_slave");
 
        User selectFromMasterAndSlaveWithoutDataSourceRouting = userService.selectFromMasterAndSlaveWithoutDataSourceRoutingInDao("1", "maple_slave");
 
        return selectFromMasterAndSlaveWithDataSourceRouting;
    }
}

UserServiceImpl


package com.gane.maple.service.impl;
 
import com.gane.maple.dao.UserDAO;
import com.gane.maple.entity.User;
import com.gane.maple.jdbc.routing.ClientDataSource;
import com.gane.maple.jdbc.routing.annotation.DataSourceRouting;
import com.gane.maple.service.UserService;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Service;
 
/**
 * @Description UserServiceImpl
 * @Date 2020/4/24 7:41
 * @Created by 王弘博
 */
@Service
public class UserServiceImpl implements UserService {
 
    @Autowired
    private UserDAO userDAO;
 
    /**
     * 把 @DataSourceRouting 放进 dao 层
     *
     * @param userId
     * @return
     */
    @Override
    public User selectByUserId(String userId) {
        User userFromMaster = userDAO.selectByUserId(userId);
        System.out.println("查询master库：" + userFromMaster);
        return userFromMaster;
    }
 
    /**
     * 把 @DataSourceRouting 放进 dao 层
     *
     * @param userName
     * @return
     */
    @Override
    public User selectByUserName(String userName) {
        User userFromSlave = userDAO.selectByUserName(userName);
        System.out.println("查询slave库：" + userFromSlave);
        return userFromSlave;
    }
 
    /**
     * 把 @DataSourceRouting 放进 dao 层
     * 观察进入aspect几次
     *
     * @param userId
     * @param userName
     * @return
     */
    @Override
    public User selectFromMasterAndSlave(String userId, String userName) {
 
        User userFromMaster = userDAO.selectByUserId(userId);
        System.out.println("查询master库：" + userFromMaster);
 
        User userFromSlave = userDAO.selectByUserName(userName);
        System.out.println("查询slave库：" + userFromSlave);
 
        return userFromMaster;
    }
 
    /**
     * 把 @DataSourceRouting 放进 service 层 和 dao 层。判断具体以哪个datasource为准
     *
     * @param userId
     * @param userName
     * @return
     */
    @DataSourceRouting(value = ClientDataSource.SLAVE)
    @Override
    public User selectFromMasterAndSlaveWithDataSourceRoutingInDao(String userId, String userName) {
 
        User userFromMaster = userDAO.selectByUserId(userId);
        System.out.println("查询master库：" + userFromMaster);
 
        User userFromSlave = userDAO.selectByUserName(userName);
        System.out.println("查询slave库：" + userFromSlave);
 
        return userFromMaster;
    }
 
    @DataSourceRouting(value = ClientDataSource.SLAVE)
    @Override
    public User selectFromMasterAndSlaveWithoutDataSourceRoutingInDao(String userId, String userName) {
 
        User userFromMaster = userDAO.selectByUserIdWithoutDataSourceRouting(userId);
        System.out.println("查询master库：" + userFromMaster);
 
        User userFromSlave = userDAO.selectByUserNameWithoutDataSourceRouting(userName);
        System.out.println("查询slave库：" + userFromSlave);
 
        return userFromMaster;
    }
 
 
}

UserDAO


package com.gane.maple.dao;
 
import com.gane.maple.entity.User;
import com.gane.maple.jdbc.routing.ClientDataSource;
import com.gane.maple.jdbc.routing.annotation.DataSourceRouting;
 
/**
 * @Description UserDAO
 * @Date 2020/4/24 7:39
 * @Created by 王弘博
 */
public interface UserDAO {
 
    @DataSourceRouting(value = ClientDataSource.MASTER)
    User selectByUserId(String userId);
 
    @DataSourceRouting(value = ClientDataSource.SLAVE)
    User selectByUserName(String userName);
 
    User selectByUserIdWithoutDataSourceRouting(String userId);
 
    User selectByUserNameWithoutDataSourceRouting(String userName);
}

10、总结

我们可以把注解 DataSourceRouting 作用在 service 接口上，也可以作用在 dao 接口上
如果只作用在 service 接口上的话，比如配置的是 slave，那么该 service 里的所有调用 dao 的地方，都会走 slave 数据源；
如果只作用在 dao 接口上的话，比如配置的是 slave，那么该 service 里的所有调用 dao 的地方，都会走 slave 数据源；
如果 service 上配置的是 master，aDao配置的是 slave，bDao配置的是 master，当走到 service 的时候，会被 DataSourceRoutingAspect 拦截到，并赋值master给 ClientDataSourceContextHolder ，当执行到 aDao 的时候，又会被 DataSourceRoutingAspect 拦截到，拿到配置在aDao上的注解slave，重写determineCurrentLookupKey 方法里会返回 slave出去，最终走的是 slave 数据源；当执行到 bDao 的时候，又会被 DataSourceRoutingAspect 拦截到，拿到配置在bDao上的注解master，则最终执行 bDao 走的是 master 数据源；所以在dao接口上配置注解的优先级要高于在service上配置，遵循就近原则；这里需要开发人员根据自己的业务来做相应的处理。