SpringBoot+MyBatis+MySQL讀寫分離（實例）

1. 引言

讀寫分離要做的事情就是對於一條SQL該選擇哪個數據庫去執行，至於誰來做選擇數據庫這件事兒，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），也就是說應用程序連接到中間件，中間件幫我們做SQL分離；第二種是應用程序自己去做分離。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，應用程序層面去做讀寫分離最大的弱點（不足之處）在於無法動態增加數據庫節點，因為數據源配置都是寫在配置中的，新增數據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

關於配置請參考：

https://www.cnblogs.com/cjsblog/p/9706370.html

3.1. maven依賴

<project> 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>
 <parent>
 <groupid>org.springframework.boot/<groupid>
 <artifactid>spring-boot-starter-parent/<artifactid>
 <version>2.0.5.RELEASE/<version>
 <relativepath> 
 /<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>
 
 /<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 

 */
@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> 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;
 }
}
/<object>

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
@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");
 }
 }
}
/<dbtypeenum>

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
@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... 判斷哪些需要讀從數據庫，其餘的走主數據庫
 */
// @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數據庫
 // 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;
 }
}
/<member>

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");
 }
}

查看控制檯

5. 工程結構

6. 參考

www.jianshu.com/p/f2f4256a2310

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

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

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

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