SpringBoot+MyBatis+MySQL读写分离

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。

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。

3.  实践

---

关于配置请参考《mysql主从复制配置》

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/> <!-- 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.  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

5.  工程结构

---

6.  参考

---