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SpringBoot+MyBatis+MySQL读写分离(实例)

编辑:005     时间:2020-11-17


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。


3.1. 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-namecom.mysql.jdbc.Driver     slave1:
      jdbc-url: jdbc:mysql://192.168.102.56:3306/test       username: pig   # 只读账户
      password: 123456       driver-class-namecom.mysql.jdbc.Driver     slave2:
      jdbc-url: jdbc:mysql://192.168.102.36:3306/test       username: pig   # 只读账户
      password: 123456       driver-class-namecom.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");
    }

}

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5. 工程结构



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