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
</plugins> </build></project>3.2. 数据源配置application.ymlspring: 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 */@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; }}这里" data-itemshowtype="0" tab="innerlink" data-linktype="2">"1.0" encoding="UTF-8"?>
"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">
4.0.0
com.cjs.example
cjs-datasource-demo
0.0.1-SNAPSHOT
jar
cjs-datasource-demo
org.springframework.boot
spring-boot-starter-parent
2.0.5.RELEASE
UTF-8
UTF-8
1.8
org.springframework.boot
spring-boot-starter-aop
org.springframework.boot
spring-boot-starter-jdbc
org.springframework.boot
spring-boot-starter-web
org.mybatis.spring.boot
mybatis-spring-boot-starter
1.3.2
org.apache.commons
commons-lang3
3.8
mysql
mysql-connector-java
runtime
org.springframework.boot
spring-boot-starter-test
test
org.springframework.boot
spring-boot-maven-plugin
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
</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. 数据源配置application.ymlspring: 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 */@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; }}这里" data-itemshowtype="0" tab="innerlink" data-linktype="2">多数据源配置
</plugins> </build></project>3.2. 数据源配置application.ymlspring: 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 */@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; }}这里" data-itemshowtype="0" tab="innerlink" data-linktype="2">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
</plugins> </build></project>3.2. 数据源配置application.ymlspring: 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 */@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; }}这里" data-itemshowtype="0" tab="innerlink" data-linktype="2" style="color: rgb(0, 0, 0);">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。
Spring Boot 最新基础教程和示例源码：https://github.com/javastacks/spring-boot-best-practice
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。另外，Spring 系列面试题和答案全部整理好了，微信搜索Java技术栈，在后台发送：面试，可以在线阅读。
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 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 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 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
