SpringBoot实现数据库读写分离

参考博客https://blog.csdn.net/qq_31708899/article/details/121577253
实现原理：翻看AbstractRoutingDataSource源码我们可以看到其中的targetDataSource可以维护一组目标数据源(采用map数据结构)，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。看到了这个，我们就可以想到怎么实现数据源切换了

#### 一 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 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>2.4.12-SNAPSHOT</version>
        <relativePath/> <!-- lookup parent from repository -->
    </parent>
    <groupId>com.ReadAndWriteSeparate</groupId>
    <artifactId>demo</artifactId>
    <version>0.0.1-SNAPSHOT</version>
    <name>ReadAndWriteSeparate</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-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>2.2.0</version>
        </dependency>

        <dependency>
            <groupId>mysql</groupId>
            <artifactId>mysql-connector-java</artifactId>
            <version>5.1.26</version>
            <scope>runtime</scope>
        </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>
        <dependency>
            <groupId>org.aspectj</groupId>
            <artifactId>aspectjweaver</artifactId>
            <version>1.9.5</version>
        </dependency>
    </dependencies>

    <build>
        <plugins>
            <plugin>
                <groupId>org.springframework.boot</groupId>
                <artifactId>spring-boot-maven-plugin</artifactId>
                <configuration>
                    <excludes>
                        <exclude>
                            <groupId>org.projectlombok</groupId>
                            <artifactId>lombok</artifactId>
                        </exclude>
                    </excludes>
                </configuration>
            </plugin>
        </plugins>
        <resources>
            <resource>
                <directory>src/main/java</directory>
                <includes>
                    <include>
                        **/*.xml
                    </include>
                </includes>
            </resource>
        </resources>
    </build>

</project>

二数据源配置

yaml配置
这里我只用一个账号模拟，生产环境下必须要分开只读账号和可读可写账号，因为主从复制中，主机可不会同步从机的数据哟

spring:
  datasource:
    master:
      jdbc-url: jdbc:mysql://localhost:3306/demo?useUnicode=true&characterEncoding=UTF-8&serverTimezone=Asia/Shanghai
      username: root
      password: root
      driver-class-name: com.mysql.jdbc.Driver
    slave1:
      jdbc-url: jdbc:mysql://localhost:3306/demo?useUnicode=true&characterEncoding=UTF-8&serverTimezone=Asia/Shanghai
      username: root
      password: root
      driver-class-name: com.mysql.jdbc.Driver
    slave2:
      jdbc-url: jdbc:mysql://localhost:3306/demo?useUnicode=true&characterEncoding=UTF-8&serverTimezone=Asia/Shanghai
      username: root
      password: root
      driver-class-name: com.mysql.jdbc.Driver

数据源配置

package com.readandwriteseparate.demo.Config;

import com.readandwriteseparate.demo.Enum.DbEnum;
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.beans.ConstructorProperties;
import java.util.HashMap;
import java.util.Map;

/**
 * @author OriginalPerson
 * @date 2021/11/25 20:25
 * @Email 2568500308@qq.com
 */
@Configuration
public class DataSourceConfig {
    //主数据源，用于写数据,特殊情况下也可用于读
    @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 routingDataSource(@Qualifier("masterDataSource") DataSource masterDataSource,
                                        @Qualifier("slave1DataSource") DataSource slave1DataSource,
                                        @Qualifier("slave2DataSource") DataSource slave2DataSource){
        Map<Object,Object> targetDataSource=new HashMap<>();
        targetDataSource.put(DbEnum.MASTER,masterDataSource);
        targetDataSource.put(DbEnum.SLAVE1,slave1DataSource);
        targetDataSource.put(DbEnum.SLAVE2,slave2DataSource);
        RoutingDataSource routingDataSource=new RoutingDataSource();
        routingDataSource.setDefaultTargetDataSource(masterDataSource);
        routingDataSource.setTargetDataSources(targetDataSource);

        return routingDataSource;
    }

}

这里我们配置了4个数据源，其中前三个数据源都是为了生成第四个路由数据源产生的，路由数据源的key我们使用枚举类型来标注,三个枚举类型分别代表数据库的类型。

package com.readandwriteseparate.demo.Enum;

/**
 * @author OriginalPerson
 * @date 2021/11/25 20:45
 * @Email: 2568500308@qq.com
 */
public enum DbEnum {
    MASTER,SLAVE1,SLAVE2;
}

三数据源切换

这里我们使用ThreadLocal将路由key设置到每个线程的上下文中这里也进行一个简单的负载均衡，轮询两个只读数据源,而访问哪个取决于counter的值，每增加1，切换一下数据源，该值为juc并发包下的原子操作类，保证其线程安全。

设置路由键，获取当前数据源的key

package com.readandwriteseparate.demo.Config;

import com.readandwriteseparate.demo.Enum.DbEnum;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

import java.util.concurrent.atomic.AtomicInteger;

/**
 * @author OriginalPerson
 * @date 2021/11/25 20:49
 * @Email: 2568500308@qq.com
 */
public class DBContextHolder {
    private static final ThreadLocal<DbEnum> contextHolder=new ThreadLocal<>();
    private static final AtomicInteger counter=new AtomicInteger(-1);

    public static void set(DbEnum type){
        contextHolder.set(type);
    }

    public static DbEnum get(){
        return contextHolder.get();
    }

    public static void master()
    {
        set(DbEnum.MASTER);
        System.out.println("切换到master数据源");
    }

    public static void slave(){
        //轮询数据源进行读操作
        int index=counter.getAndIncrement() % 2;
        if(counter.get()>9999){
            counter.set(-1);
        }
        if(index==0){
            set(DbEnum.SLAVE1);
            System.out.println("切换到slave1数据源");
        }else {
            set(DbEnum.SLAVE2);
            System.out.println("切换到slave2数据源");
        }
    }
}

确定当前数据源

这个比较重要，其继承AbstractRoutingDataSource类，重写了determineCurrentLookupKey方法，该方法决定当前数据源的key，对应于上文配置数据源的map集合中的key，让该方法返回我们定义的ThreadLocal中存储的key，即可实现数据源切换。


import org.springframework.jdbc.datasource.lookup.AbstractRoutingDataSource;
import org.springframework.lang.Nullable;

/**
 * @author OriginalPerson
 * @date 2021/11/25 20:47
 * @Email: 2568500308@qq.com
 */
public class RoutingDataSource extends AbstractRoutingDataSource {
    @Nullable
    @Override
    protected Object determineCurrentLookupKey() {
        return DBContextHolder.get();
    }
}

mybatis配置三个数据源

package com.readandwriteseparate.demo.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.jdbc.datasource.DataSourceTransactionManager;
import org.springframework.transaction.PlatformTransactionManager;
import org.springframework.transaction.annotation.EnableTransactionManagement;

import javax.annotation.Resource;
import javax.sql.DataSource;

/**
 * @author OriginalPerson
 * @date 2021/11/25 22:17
 * @Email 2568500308@qq.com
 */
@EnableTransactionManagement
@Configuration
public class MybatisConfig {

    @Resource(name = "routingDataSource")
    private DataSource routingDataSource;

    @Bean
    public SqlSessionFactory sessionFactory() throws Exception {
        SqlSessionFactoryBean sqlSessionFactoryBean=new SqlSessionFactoryBean();
        sqlSessionFactoryBean.setDataSource(routingDataSource);
        return sqlSessionFactoryBean.getObject();
    }

    @Bean
    public PlatformTransactionManager platformTransactionManager(){
        return new DataSourceTransactionManager(routingDataSource);
    }
}

四特殊处理master主库读数据操作、

在某些场景下，我们需要实时读取到更新过的值，例如某个业务逻辑，在插入一条数据后，需要立即查询据，因为读写分离我们用的是主从复制架构，它是异步操作，串行复制数据，所以必然存在主从延迟问题，对于刚插入的数据，如果要马上取出，读从库是没有数据的，因此需要直接读主库，这里我们通过一个Master注解来实现，被该注解标注的方法将直接在主库数据

注解

package com.readandwriteseparate.demo.annotation;

/**
 * @author OriginalPerson
 * @date 2021/11/26 13:28
 * @Email 2568500308@qq.com
 */


public @interface Master {
}

APO切面处理

package com.readandwriteseparate.demo.Aspect;

import com.readandwriteseparate.demo.Config.DBContextHolder;
import org.aspectj.lang.annotation.Aspect;
import org.aspectj.lang.annotation.Before;
import org.aspectj.lang.annotation.Pointcut;
import org.springframework.stereotype.Component;

/**
 * @author OriginalPerson
 * @date 2021/11/26 13:23
 * @Email 2568500308@qq.com
 */

@Aspect
@Component
public class DataSourceAop {
   
   // 非master注解且有关读的方法操作从库
   @Pointcut("!@annotation(com.readandwriteseparate.demo.annotation.Master)" +
            " && (execution(* com.readandwriteseparate.demo.Service..*.select*(..)))" +
            " || execution(* com.readandwriteseparate.demo.Service..*.get*(..)))")
    public void readPointcut(){

    }

  
  // 有master注解或者有关处理数据的操作主库  @Pointcut("@annotation(com.readandwriteseparate.demo.annotation.Master) " +
            "|| execution(* com.readandwriteseparate.demo.Service..*.insert*(..)) " +
            "|| execution(* com.readandwriteseparate.demo.Service..*.add*(..)) " +
            "|| execution(* com.readandwriteseparate.demo.Service..*.update*(..)) " +
            "|| execution(* com.readandwriteseparate.demo.Service..*.edit*(..)) " +
            "|| execution(* com.readandwriteseparate.demo.Service..*.delete*(..)) " +
            "|| execution(* com.readandwriteseparate.demo.Service..*.remove*(..))")
    public void writePointcut() {

    }

    @Before("readPointcut()")
    public void read(){
        DBContextHolder.slave();
    }

    @Before("writePointcut()")
    public void write(){
        DBContextHolder.master();
    }
}

五读写分离案例使用

实体类

package com.readandwriteseparate.demo.Domain;

import lombok.AllArgsConstructor;
import lombok.Data;
import lombok.NoArgsConstructor;

import java.io.Serializable;

/**
 * @author OriginalPerson
 * @date 2021/11/26 23:15
 * @Email 2568500308@qq.com
 */
@Data
@AllArgsConstructor
@NoArgsConstructor
public class User implements Serializable {
    private Integer id;
    private String name;
    private String sex;
}

Dao层

package com.readandwriteseparate.demo.Dao;

import com.readandwriteseparate.demo.Domain.User;
import org.apache.ibatis.annotations.Param;

import java.util.List;

/**
 * @author OriginalPerson
 * @date 2021/11/26 23:16
 * @Email 2568500308@qq.com
 */
public interface UserMapper {
    public List<User> selectAllUser();

    public Integer insertUser(@Param("user") User user);

    public User selectOneById(@Param("id") Integer id);
}

xml

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN" "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
<mapper namespace="com.readandwriteseparate.demo.Dao.UserMapper">

    <resultMap id="user" type="com.readandwriteseparate.demo.Domain.User">
        <id property="id" column="id"></id>
        <result property="name" column="name"></result>
        <result property="sex" column="sex"></result>
    </resultMap>

    <select resultMap="user" id="selectAllUser" resultType="com.readandwriteseparate.demo.Domain.User">
        select * from user
    </select>

    <insert id="insertUser" parameterType="com.readandwriteseparate.demo.Domain.User">
        insert into user(name,sex) values(#{user.name},#{user.sex})
    </insert>

    <select id="selectOneById" parameterType="java.lang.Integer" resultMap="user">
        select * from user where id=#{id}
    </select>
</mapper>

service

package com.readandwriteseparate.demo.Service;

import com.readandwriteseparate.demo.Dao.UserMapper;
import com.readandwriteseparate.demo.Domain.User;
import com.readandwriteseparate.demo.annotation.Master;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Service;

import java.util.List;

/**
 * @author OriginalPerson
 * @date 2021/11/27 0:07
 * @Email 2568500308@qq.com
 */

@Service
public class UserService {

    @Autowired
    private UserMapper userMapper;

    public List<User> getAllUser(){
        return userMapper.selectAllUser();
    }

    public Integer addUser(User user){
        return userMapper.insertUser(user);
    }

    /*
    * 特殊情况下，需要从主库查询时
    * 例如某些业务更新数据后需要马上查询，因为主从复制有延迟，所以需要从主库查询
    * 添加@Master注解即可从主库查询
    *
    * 该注解实现比较简单，在aop切入表达式中进行判断即可
    * */
    @Master
    public User selectOneById(Integer id){
        return userMapper.selectOneById(id);
    }
}

单元测试代码

package com.readandwriteseparate.demo;

import com.readandwriteseparate.demo.Dao.UserMapper;
import com.readandwriteseparate.demo.Domain.User;
import com.readandwriteseparate.demo.Service.UserService;
import org.junit.jupiter.api.Test;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.test.context.SpringBootTest;

@SpringBootTest
class ReadAndWriteSeparateApplicationTests {

    @Autowired
    private UserService userService;
    @Test
    void contextLoads() throws InterruptedException {
        User user=new User();
        user.setName("赵六");
        user.setSex("男");
        System.out.println("插入一条数据");
        userService.addUser(user);
        for (int i = 0; i <4 ; i++) {
            System.out.println("开始查询数据");
            System.out.println("第"+(i+1)+"次查询");
            userService.getAllUser();
            System.out.println("-------------------------分割线------------------------");
        }
        System.out.println("强制查询主库");
        userService.selectOneById(1);
    }

}