SpringBoot + MyBatis + MySQL讀寫分離實踐!

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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，要麼中間件幫我們做，要麼程序自己做。因此，一般來講，讀寫分離有兩種實現方式。第一種是依靠中間件（比如：MyCat），也就是說應用程式連接到中間件，中間件幫我們做SQL分離；第二種是應用程式自己去做分離。這裡我們選擇程序自己來做，主要是利用Spring提供的路由數據源，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，因為數據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

基於特定的查找key路由到特定的數據源。它內部維護了一組目標數據源，並且做了路由key與目標數據源之間的映射，提供基於key查找數據源的方法。

3. 實踐

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. 數據源配置

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

多數據源配置

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;/*** 關於數據源配置，參考SpringBoot官方文檔第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(); } @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個路由數據源。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數據源。

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; @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數據源。

3.3 設置路由key / 查找數據源

目標數據源就是那前3個這個我們是知道的，但是使用的時候是如果查找數據源的呢？

首先，我們定義一個枚舉來代表這三個數據源

package com.cjs.example.enums;public enum DBTypeEnum {MASTER, SLAVE1, SLAVE2;}

接下來，通過ThreadLocal將數據源設置到每個線程上下文中

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(); }}

設置路由key

默認情況下，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類型（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;@Servicepublic 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數據讀 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)@SpringBootTestpublic 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"); }}

查看控制臺

5. 工程結構

6. 參考

https://www.jianshu.com/p/f2f4256a2310http://www.cnblogs.com/gl-developer/p/6170423.htmlhttps://www.cnblogs.com/huangjuncong/p/8576935.htmlhttps://blog.csdn.net/liu976180578/article/details/77684583