SpringBoot+MyBatis+MySQL讀寫分離實戰

2019 年 10 月 7 日
筆記

來源:http://suo.im/5mB8gj

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。這裡我們選擇程式自己來做，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

關於配置請參考：https://www.cnblogs.com/cjsblog/p/9706370.html

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, 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  @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)  @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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