Spring Boot + MyBatis + MySQL to realize read-write separation

Keywords: Java

Author: Waste elder martial brother
Source: https://www.cnblogs.com/cjsblog/p/9712457.html

1. Introduction

The task of read-write separation is to select which database to execute an SQL. As for who will select the database, there are no more than two. Either the middleware will help us or the program will do it by itself.

Therefore, generally speaking, there are two ways to realize read-write separation. The first is to rely on Middleware (such as MyCat), that is, the application is connected to the middleware, which helps us separate SQL; The second is the separation of the application itself. Here we choose the program to do it ourselves, mainly using the routing data source provided by Spring and AOP

However, the biggest weakness (deficiency) of separating read and write at the application level is that it is unable to dynamically add database nodes, because the data source configuration is written in the configuration. Adding a new database means adding a new data source, which will inevitably change the configuration and restart the application. Of course, the advantage is that it is relatively simple.

2,AbstractRoutingDataSource

Route to a specific data source based on a specific lookup key. It internally maintains a set of target data sources, maps the routing key to the target data source, and provides a method to find the data source based on the key.

3. Practice

3.1. maven dependency

<?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/> <!-- lookup parent from repository -->
    </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>


            <!--<plugin>
                <groupId>org.mybatis.generator</groupId>
                <artifactId>mybatis-generator-maven-plugin</artifactId>
                <version>1.3.5</version>
                <dependencies>
                    <dependency>
                        <groupId>mysql</groupId>
                        <artifactId>mysql-connector-java</artifactId>
                        <version>5.1.46</version>
                    </dependency>
                </dependencies>
                <configuration>
                    <configurationFile>${basedir}/src/main/resources/myBatisGeneratorConfig.xml</configurationFile>
                    <overwrite>true</overwrite>
                </configuration>
                <executions>
                    <execution>
                        <id>Generate MyBatis Artifacts</id>
                        <goals>
                            <goal>generate</goal>
                        </goals>
                    </execution>
                </executions>
            </plugin>-->

        </plugins>
    </build>
</project>

3.2. Data source configuration

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   # Read only account
      password: 123456
      driver-class-name: com.mysql.jdbc.Driver
    slave2:
      jdbc-url: jdbc:mysql://192.168.102.36:3306/test
      username: pig   # Read only account
      password: 123456
      driver-class-name: com.mysql.jdbc.Driver

Multi data source configuration

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;

/**
 * For data source configuration, refer to chapter 79 Data Access in the official SpringBoot document
 * 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;
    }

}

Here, we configure 4 data sources, 1 master, 2 slave and 1 routing data source. The first three data sources are used to generate the fourth data source, and we will only use the last routing data source later.

MyBatis configuration

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);
    }
}

Since there are now four data sources in the Spring container, we need to manually specify an explicit data source for the transaction manager and MyBatis.

3.3. Set routing key / find data source

The target data source is the first three. We know this, but what if we find the data source when using it?

First, we define an enumeration to represent the three data sources

package com.cjs.example.enums;

public enum DBTypeEnum {

    MASTER, SLAVE1, SLAVE2;

}

Next, set the data source to each thread context through ThreadLocal

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("Switch to master");
    }

    public static void slave() {
        //  polling 
        int index = counter.getAndIncrement() % 2;
        if (counter.get() > 9999) {
            counter.set(-1);
        }
        if (index == 0) {
            set(DBTypeEnum.SLAVE1);
            System.out.println("Switch to slave1");
        }else {
            set(DBTypeEnum.SLAVE2);
            System.out.println("Switch to slave2");
        }
    }

}

Get routing 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();
    }

}

Set routing key

By default, all queries follow the slave database, and insert / modify / delete follow the master database. We distinguish operation types (CRUD) by method names

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();
    }


    /**
     * Another way to write it: if...else... Judge what needs to be read from the slave database, and the rest go to the master database
     */
//    @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();
//        }
//    }
}

In general, there are special cases. In special cases, we need to force the reading of the primary database. In this case, we define a primary key and use the annotation to mark the reading primary database

package com.cjs.example.annotation;

public @interface Master {
}

For example, suppose we have a table 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) {
        //  Some read operations must read the primary database
        //  For example, get wechat access_token, because the master-slave synchronization may be delayed during peak periods
        //  In this case, it is necessary to force reading from the master data
        return null;
    }
}

4. Testing

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");
    }

}

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