SpringBoot+MyBatis+MySQL读写分离实战

JavaFish

发布于 2019-12-04 11:50:23

3630

发布于 2019-12-04 11:50:23

文章被收录于专栏：狗哥的 Java 世界狗哥的 Java 世界

题图：pexels

参考：https://www.jianshu.com/p/f2f4256a2310

http://www.cnblogs.com/gl-developer/p/6170423.html

https://www.cnblogs.com/huangjuncong/p/8576935.html

https://blog.csdn.net/liu976180578/article/details/77684583

预计阅读时间：5.20分钟

1.前言

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：

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/testusername: rootpassword: 123456driver-class-name: com.mysql.jdbc.Driverslave1:jdbc-url: jdbc:mysql://192.168.102.56:3306/testusername: pig # 只读账户password: 123456driver-class-name: com.mysql.jdbc.Driverslave2:jdbc-url: jdbc:mysql://192.168.102.36:3306/testusername: pig # 只读账户password: 123456driver-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*/
@Configurationpublic 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();}
@Beanpublic 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@Configurationpublic class MyBatisConfig {
@Resource(name = "myRoutingDataSource")private DataSource myRoutingDataSource;
@Beanpublic SqlSessionFactory sqlSessionFactory() throws Exception {SqlSessionFactoryBean sqlSessionFactoryBean = new SqlSessionFactoryBean();sqlSessionFactoryBean.setDataSource(myRoutingDataSource);sqlSessionFactoryBean.setMapperLocations(new PathMatchingResourcePatternResolver().getResources("classpath:mapper/*.xml"));return sqlSessionFactoryBean.getObject();}
@Beanpublic 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@Overrideprotected 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@Componentpublic 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;
@Servicepublic class MemberServiceImpl implements MemberService {
@Autowiredprivate MemberMapper memberMapper;
@Transactional@Overridepublic int insert(Member member) {return memberMapper.insert(member);}
@Master@Overridepublic int save(Member member) {return memberMapper.insert(member);}
@Overridepublic List<Member> selectAll() {return memberMapper.selectByExample(new MemberExample());}
@Master@Overridepublic 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)@SpringBootTestpublic class CjsDatasourceDemoApplicationTests {
@Autowiredprivate MemberService memberService;
@Testpublic void testWrite() {Member member = new Member();member.setName("zhangsan");memberService.insert(member);}
@Testpublic void testRead() {for (int i = 0; i < 4; i++) {memberService.selectAll();}}
@Testpublic void testSave() {Member member = new Member();member.setName("wangwu");memberService.save(member);}
@Testpublic void testReadFromMaster() {memberService.getToken("1234");}
}

查看控制台

5.工程结构

推荐阅读：
《SpringBoot整合easyexcel实现Excel导入》
《良心推荐，两个比某度好用的搜索引擎》

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