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摘要: 原创出处 http://cnblogs.com/cjsblog/p/9712457.html 「狂乱的贵公子」欢迎转载,保留摘要,谢谢!


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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。

img


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。

img


3. 实践

关于配置请参考:

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

3.1. maven依赖

<?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. 数据源配置

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
*/

@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;
}

}

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。

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。

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<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<Member> 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 < 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");
}

}

查看控制台

img

img


5. 工程结构

img


6. 参考

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

文章目录
  1. 1. 1. 引言
  2. 2. 2. AbstractRoutingDataSource
  3. 3. 3. 实践
    1. 3.1. 3.1. maven依赖
    2. 3.2. 3.2. 数据源配置
    3. 3.3. 3.3. 设置路由key / 查找数据源
  4. 4. 4. 测试
  5. 5. 5. 工程结构
  6. 6. 6. 参考