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SpringBoot+MyBatis+MySQL读写分离实战

2019-07-17 框架整合
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
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。

SpringBoot+MyBatis+MySQL读写分离实战 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:https://www.cnblogs.com/cjsblog/p/9706370.html

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"); } }

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