SpringBoot+MyBatis+MySQL读写分离实战

Java技术江湖

发布于 2019-09-24 17:50:27

4000

发布于 2019-09-24 17:50:27

文章被收录于专栏：微信公众号【Java技术江湖】微信公众号【Java技术江湖】

来源:http://suo.im/5mB8gj

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：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");
 }

}

查看控制台