SpringBoot+MyBatis+MySQL讀寫分離

MySQL MyBatis SpringBoot · 發表 2018-09-27 12:46:00

摘要： 1. 引言讀寫分離要做的事情就是對於一條SQL該選擇哪個資料庫去執行，至於誰來做選擇資料庫這件事兒，無非兩個，要麼中介軟體幫我們做，要麼程式自己做。因此，一般來講，讀寫分離有兩種實現方式。第一種是依靠中介軟體（比如：MyCat），也就是說應用程式連線到中介軟體，中介軟體幫我們做SQL分...

1. 引言

讀寫分離要做的事情就是對於一條SQL該選擇哪個資料庫去執行，至於誰來做選擇資料庫這件事兒，無非兩個，要麼中介軟體幫我們做，要麼程式自己做。因此，一般來講，讀寫分離有兩種實現方式。第一種是依靠中介軟體（比如：MyCat），也就是說應用程式連線到中介軟體，中介軟體幫我們做SQL分離；第二種是應用程式自己去做分離。這裡我們選擇程式自己來做，主要是利用Spring提供的路由資料來源，以及AOP

然而，應用程式層面去做讀寫分離最大的弱點（不足之處）在於無法動態增加資料庫節點，因為資料來源配置都是寫在配置中的，新增資料庫意味著新加一個數據源，必然改配置，並重啟應用。當然，好處就是相對簡單。

2. AbstractRoutingDataSource

基於特定的查詢key路由到特定的資料來源。它內部維護了一組目標資料來源，並且做了路由key與目標資料來源之間的對映，提供基於key查詢資料來源的方法。

3. 實踐

關於配置請參考《 ofollow,noindex"> MySQL主從複製配置》

3.1. maven依賴

<?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. 資料來源配置

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# 只讀賬戶
password: 123456
driver-class-name: com.mysql.jdbc.Driver
slave2:
jdbc-url: jdbc:mysql://192.168.102.36:3306/test
username: pig# 只讀賬戶
password: 123456
driver-class-name: com.mysql.jdbc.Driver

多資料來源配置

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;

/**
 * 關於資料來源配置，參考SpringBoot官方文件第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;
}

}

這裡，我們配置了4個數據源，1個master，2兩個slave，1個路由資料來源。前3個數據源都是為了生成第4個數據源，而且後續我們只用這最後一個路由資料來源。

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);
}
}

由於Spring容器中現在有4個數據源，所以我們需要為事務管理器和MyBatis手動指定一個明確的資料來源。

3.3. 設定路由key / 查詢資料來源

目標資料來源就是那前3個這個我們是知道的，但是使用的時候是如果查詢資料來源的呢？

首先，我們定義一個列舉來代表這三個資料來源

package com.cjs.example.enums;

public enum DBTypeEnum {

MASTER, SLAVE1, SLAVE2;

}

接下來，通過ThreadLocal將資料來源設定到每個執行緒上下文中

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("切換到master");
}

public static void slave() {
//輪詢
int index = counter.getAndIncrement() % 2;
if (counter.get() > 9999) {
counter.set(-1);
}
if (index == 0) {
set(DBTypeEnum.SLAVE1);
System.out.println("切換到slave1");
}else {
set(DBTypeEnum.SLAVE2);
System.out.println("切換到slave2");
}
}

}

獲取路由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();
}

}

設定路由key

預設情況下，所有的查詢都走從庫，插入/修改/刪除走主庫。我們通過方法名來區分操作型別（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();
}


/**
* 另一種寫法：if...else...判斷哪些需要讀從資料庫，其餘的走主資料庫
*/
//@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();
//}
//}
}

有一般情況就有特殊情況，特殊情況是某些情況下我們需要強制讀主庫，針對這種情況，我們定義一個主鍵，用該註解標註的就讀主庫

package com.cjs.example.annotation;

public @interface Master {
}

例如，假設我們有一張表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) {
//有些讀操作必須讀主資料庫
//比如，獲取微信access_token，因為高峰時期主從同步可能延遲
//這種情況下就必須強制從主資料讀
return null;
}
}

4. 測試

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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