实现读写分离SpringBoot+MyBatis+Druid

实现读写分离

SpringBoot+MyBatis+Druid

1.读写分离概念理解

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。

读写分离涉及到数据库主从同步

数据库主从同步：https://www.cnblogs.com/cjsblog/p/9706370.html

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。

开始吧！

工程结构

1.引入maven依赖

    4.0.0
    
        org.springframework.boot
        spring-boot-starter-parent
        2.4.0
         
    
    com.example
    multidatasource
    0.0.1-SNAPSHOT
    multidatasource
    读写分离多数据源

    
        1.8
    

    
        
            org.springframework.boot
            spring-boot-starter-web
        
        
            org.springframework.boot
            spring-boot-starter-aop
        
        
            org.mybatis.spring.boot
            mybatis-spring-boot-starter
            2.1.2
        
         
              org.springframework.boot
             spring-boot-configuration-processor
             true
         
        
            mysql
            mysql-connector-java
            runtime
        
        
            com.alibaba
            druid-spring-boot-starter
            1.1.10
        
        
            org.springframework.boot
            spring-boot-starter-jdbc
        
        
            org.projectlombok
            lombok
            true
        
        
            org.springframework.boot
            spring-boot-starter-test
            test
        
    

    
        
            
                org.springframework.boot
                spring-boot-maven-plugin
            
        
    

2.数据源配置

spring.datasource.master.url=jdbc:mysql://localhost:3306/db01?useUnicode=true&characterEncoding=utf8&serverTimezone=UTC
spring.datasource.master.username=root
spring.datasource.master.password=
spring.datasource.master.type=com.alibaba.druid.pool.DruidDataSource

spring.datasource.slave1.url=jdbc:mysql://localhost:3306/db02?useUnicode=true&characterEncoding=utf8&serverTimezone=UTC
spring.datasource.slave1.username=root
spring.datasource.slave1.password=
spring.datasource.slave1.type=com.alibaba.druid.pool.DruidDataSource

spring.datasource.slave2.url=jdbc:mysql://localhost:3306/db03?useUnicode=true&characterEncoding=utf8&serverTimezone=UTC
spring.datasource.slave2.username=root
spring.datasource.slave2.password=
spring.datasource.slave2.type=com.alibaba.druid.pool.DruidDataSource






#Spring Boot 默认是不注入这些属性值的，需要自己绑定
#druid 数据源专有配置
#配置初始化大小、最小、最大
spring.datasource.initialSize= 5
spring.datasource.minIdle= 5
spring.datasource.maxActive= 20
#配置获取连接等待超时的时间
spring.datasource.maxWait= 60000
#配置间隔多久才进行一次检测，检测需要关闭的空闲连接，单位是毫秒
spring.datasource.timeBetweenEvictionRunsMillis= 60000
#配置一个连接在池中最小生存的时间，单位是毫秒
spring.datasource.minEvictableIdleTimeMillis= 300000
#用来检测连接是否有效的sql，要求是一个查询语句，常用select 'x'。
# 如果validationQuery为null，testOnBorrow、testOnReturn、testWhileIdle都不会起作用。
spring.datasource.validationQuery=SELECT 1 FROM DUAL
spring.datasource.testWhileIdle=true
spring.datasource.testOnBorrow=false
spring.datasource.testOnReturn=false

#配置监控统计拦截的filters，stat:监控统计、log4j：日志记录、wall：防御sql注入
#如果允许时报错  java.lang.ClassNotFoundException: org.apache.log4j.Priority
#则导入 log4j 依赖即可，Maven 地址： https://mvnrepository.com/artifact/log4j/log4j
spring.datasource.filters=stat,wall,log4j
#是否缓存preparedStatement，也就是PSCache。PSCache对支持游标的数据库性能提升巨大，比如说oracle。在mysql下建议关闭。
pring.datasource.poolPreparedStatements= true
spring.datasource.maxPoolPreparedStatementPerConnectionSize= 20
spring.datasource.useGlobalDataSourceStat= true

# 配置监控统计拦截的filters
spring.datasource.stat-view-servlet.url-pattern=/druid/*
spring.datasource.stat-view-servlet.reset-enable= false
spring.datasource.druid.stat-view-servlet.login-username=admin

spring.datasource.druid.stat-view-servlet.login-password=123
spring.datasource.druid.stat-view-servlet.enabled=true

#设置ip黑名单和白名单
#spring.datasource.druid.stat-view-servlet.allow=127.0.0.1
#spring.datasource.druid.stat-view-servlet.deny=

#过滤所有请求
spring.datasource.url-pattern= /*
#排除哪些请求
spring.datasource.web-stat-filter.exclusions= "*.js,*.gif,*.jpg,*.bmp,*.png,*.css,*.ico,/druid/*"

3.加载数据库配置DataSourceConfig

package com.example.multidatasource.config;

import com.alibaba.druid.pool.DruidDataSource;
import com.alibaba.druid.spring.boot.autoconfigure.DruidDataSourceBuilder;
import com.example.multidatasource.bean.MyRoutingDataSource;
import com.example.multidatasource.type.DBTypeEnum;
import lombok.extern.slf4j.Slf4j;
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 sun.rmi.runtime.Log;

import javax.sql.DataSource;
import java.util.HashMap;
import java.util.Map;

/**
 * @create: 2020-11-16 00:28
 **/
@Configuration
@Slf4j
public class DataSourceConfig {

    /*
    * HikariDataSource改为druid
    * */
    @Bean
    @ConfigurationProperties(prefix = "spring.datasource.master")
    public DataSource masterDataSource(){
        return DruidDataSourceBuilder.create().build();
    }
    @Bean
    @ConfigurationProperties(prefix = "spring.datasource.slave1")
    public DataSource slave1DataSource(){
        return DruidDataSourceBuilder.create().build();
    }
    @Bean
    @ConfigurationProperties(prefix = "spring.datasource.slave2")
    public DataSource slave2DataSource(){
        return DruidDataSourceBuilder.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);
        log.info(targetDataSources.toString());
        MyRoutingDataSource myRoutingDataSource = new MyRoutingDataSource();
        myRoutingDataSource.setDefaultTargetDataSource(masterDataSource);
        myRoutingDataSource.setTargetDataSources(targetDataSources);
        return myRoutingDataSource;
    }

/*
    SpringBoot 默认使用 HikariDataSource
    @Bean
    @ConfigurationProperties(prefix = "spring.datasource.master")
    public DataSource masterDataSource(){
        log.info(DataSourceBuilder.create().build().toString());
        return DataSourceBuilder.create().build();
    }
    @Bean
    @ConfigurationProperties(prefix = "spring.datasource.slave1")
    public DataSource slave1DataSource(){
        return DataSourceBuilder.create().build();
    }
    @Bean
    @ConfigurationProperties(prefix = "spring.datasource.slave2")
    public DataSource slave2DataSource(){
        return DataSourceBuilder.create().build();
    }*/

/*    spring.datasource.master.jdbc-url= jdbc:mysql://localhost:3306/db01?useUnicode=true&characterEncoding=utf8&serverTimezone=UTC
    spring.datasource.master.username= root
    spring.datasource.master.password= 
    spring.datasource.master.driver-class-name= com.mysql.jdbc.Driver

    spring.datasource.slave1.jdbc-url= jdbc:mysql://localhost:3306/db02?useUnicode=true&characterEncoding=utf8&serverTimezone=UTC
    spring.datasource.slave1.username= root
    spring.datasource.slave1.password= 
    spring.datasource.slave1.driver-class-name= com.mysql.jdbc.Driver

    spring.datasource.slave2.jdbc-url= jdbc:mysql://localhost:3306/db03?useUnicode=true&characterEncoding=utf8&serverTimezone=UTC
    spring.datasource.slave2.username= root
    spring.datasource.slave2.password= 
    spring.datasource.slave2.driver-class-name= com.mysql.jdbc.Driver*/

}

4.MyBatis配置

package com.example.multidatasource.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;

/**
 * @create: 2020-11-16 01:08
 **/
@EnableTransactionManagement
@Configuration
public class MybatisConfig {
    @Resource(name = "myRoutingDataSource")
    private DataSource 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。*/
    @Bean
    public SqlSessionFactory sqlSessionFactory() throws Exception {

        SqlSessionFactoryBean sqlSessionFactoryBean = new SqlSessionFactoryBean();
        sqlSessionFactoryBean.setDataSource(myRoutingDataSource);
        //我采取的是注解式sql，如果加上扫描，但包下无mapper.xml会报错
        //sqlSessionFactoryBean.setMapperLocations(new PathMatchingResourcePatternResolver().getResources("classpath:mapper/*.xml"));

        return sqlSessionFactoryBean.getObject();
    }
    @Bean
    public PlatformTransactionManager platformTransactionManager() {
        return new DataSourceTransactionManager(myRoutingDataSource);
    }
}

5.数据源名枚举区分

public enum  DBTypeEnum {
    MASTER,SLAVE1,SLAVE2
}

6. 线程上下文工具

contextHolder 是线程变量，因为每个请求是一个线程，所以通过这样来区分使用哪个库
      determineCurrentLookupKey是重写的AbstractRoutingDataSource的方法，
      主要是确定当前应该使用哪个数据源的key，因为AbstractRoutingDataSource 中保存的多个数据源是通过Map的方式保存的

package com.example.multidatasource.bean;

import com.example.multidatasource.type.DBTypeEnum;
import lombok.extern.slf4j.Slf4j;
import org.springframework.stereotype.Component;

import java.util.concurrent.atomic.AtomicInteger;

/**
 * @create: 2020-11-16 01:00
 **/
@Slf4j
@Component
public class DBContextHolder {

    /*
    * contextHolder 是线程变量，因为每个请求是一个线程，所以通过这样来区分使用哪个库
      determineCurrentLookupKey是重写的AbstractRoutingDataSource的方法，
      主要是确定当前应该使用哪个数据源的key，因为AbstractRoutingDataSource 中保存的多个数据源是通过Map的方式保存的
    * */
    private static final ThreadLocal contextHolder=new ThreadLocal<>();

    private static final AtomicInteger counter =new AtomicInteger(-1);

    //设置当前线程所用数据库类型
    public static void set(DBTypeEnum dbType){
        contextHolder.set(dbType);
    }

    //获取当前线程所用数据类型
    public static DBTypeEnum get() {
        return contextHolder.get();
    }
    public static void master() {
        set(DBTypeEnum.MASTER);
        log.info("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);
            log.info("切换到slave1");
        }else {
            set(DBTypeEnum.SLAVE2);
            log.info("切换到slave2");
        }
    }

}

7.获取路由Key

package com.example.multidatasource.bean;

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

/**
 * @program: learn
 * @description:获取路由key
 **/
public class MyRoutingDataSource extends AbstractRoutingDataSource {
    @Override
    @Nullable
    protected Object determineCurrentLookupKey() {
        return DBContextHolder.get();
    }
}

8.默认情况下，所有的查询都走从库，插入/修改/删除走主库。我们使用AOP面向切面通过方法名来区分操作类型（CRUD）

package com.example.multidatasource.aop;

import com.example.multidatasource.bean.DBContextHolder;
import org.aspectj.lang.annotation.Aspect;
import org.aspectj.lang.annotation.Before;
import org.aspectj.lang.annotation.Pointcut;
import org.springframework.stereotype.Component;

/**
 * @create: 2020-11-16 01:18
 **/
@Aspect
@Component
public class DataSourceAspect {

    @Pointcut("!@annotation(com.example.multidatasource.annotation.Master) " +
            "&& (execution(* com.example.multidatasource.service..*.select*(..)) " +
            "|| execution(* com.example.multidatasource.service..*.get*(..)))")
    public void readPointcut(){

    }
    @Pointcut("@annotation(com.example.multidatasource.annotation.Master) " +
            "|| execution(* com.example.multidatasource.service..*.insert*(..)) " +
            "|| execution(* com.example.multidatasource.service..*.add*(..)) " +
            "|| execution(* com.example.multidatasource.service..*.update*(..)) " +
            "|| execution(* com.example.multidatasource.service..*.edit*(..)) " +
            "|| execution(* com.example.multidatasource.service..*.delete*(..)) " +
            "|| execution(* com.example.multidatasource.service..*.remove*(..))")
    public void writePointcut(){

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

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


}

8.1 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

/*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*/
public @interface Master {
}

9.实体类+DAO+Service

package com.example.multidatasource.entity;

import lombok.Data;


@Data
public class User {
    private String id;
    private String name;

    public User(String id, String name) {
        this.id = id;
        this.name = name;
    }
}

package com.example.multidatasource.dao;

import com.example.multidatasource.entity.User;
import org.apache.ibatis.annotations.Insert;
import org.apache.ibatis.annotations.Mapper;
import org.apache.ibatis.annotations.Param;
import org.apache.ibatis.annotations.Select;
import org.springframework.stereotype.Repository;

import java.util.List;


@Mapper
@Repository
public interface UserDao {

    @Select("select * from user")
    public List selectAllUser();

    @Insert("insert into user(id,name) values(#{user.id},#{user.name})")
    public int  insertUser(@Param("user") User user);
}

package com.example.multidatasource.service;

import com.example.multidatasource.dao.UserDao;
import com.example.multidatasource.entity.User;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Service;

import java.util.List;


@Service
public class UserService {

    @Autowired
    private UserDao userDao;


    public List selectAllUser(){
       return userDao.selectAllUser();
    }

    public int  insertUser(User user){
        return userDao.insertUser(user);
    }

}

10.测试类

package com.example.multidatasource;

import com.example.multidatasource.entity.User;
import com.example.multidatasource.service.UserService;
import org.junit.jupiter.api.Test;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.test.context.SpringBootTest;

import java.util.List;
import java.util.Random;
import java.util.UUID;

@SpringBootTest
class MultidatasourceApplicationTests {

    @Autowired
    UserService userService;
    @Test
    void contextLoads() {
    }
    @Test
    public void testWrite() {

        userService.insertUser(new User(UUID.randomUUID().toString(),"XXX"));
    }

    @Test
    public void testRead() {
        for (int i = 0; i < 4; i++) {
            List users = userService.selectAllUser();
            System.out.println(users.toString());
        }
    }

}

测试插入，走master

测试查询，轮询走slave1/2

6. 参考

• www.jianshu.com/p/f2f4256a2310
• www.cnblogs.com/gl-developer/p/6170423.html
• www.cnblogs.com/huangjuncong/p/8576935.html
• blog.csdn.net/liu976180578/article/details/77684583
• cnblogs.com/cjsblog/p/9712457.html