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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。
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。实践
关于配置请参考:3.1. maven依赖
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
3.2. 数据源配置
application.ymlspring:datasource:master:jdbc-url: jdbc:mysql://192.168.102.31:3306/testusername: rootpassword: 123456driver-class-name: com.mysql.jdbc.Driverslave1:jdbc-url: jdbc:mysql://192.168.102.56:3306/testusername: pig # 只读账户password: 123456driver-class-name: com.mysql.jdbc.Driverslave2:jdbc-url: jdbc:mysql://192.168.102.36:3306/testusername: pig # 只读账户password: 123456driver-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();}@Beanpublic DataSource myRoutingDataSource(@Qualifier("masterDataSource") DataSource masterDataSource,@Qualifier("slave1DataSource") DataSource slave1DataSource,@Qualifier("slave2DataSource") DataSource slave2DataSource) {Map
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@Configurationpublic class MyBatisConfig {@Resource(name = "myRoutingDataSource")private DataSource myRoutingDataSource;@Beanpublic SqlSessionFactory sqlSessionFactory() throws Exception {SqlSessionFactoryBean sqlSessionFactoryBean = new SqlSessionFactoryBean();sqlSessionFactoryBean.setDataSource(myRoutingDataSource);sqlSessionFactoryBean.setMapperLocations(new PathMatchingResourcePatternResolver().getResources("classpath:mapper/*.xml"));return sqlSessionFactoryBean.getObject();}@Beanpublic 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 ThreadLocalcontextHolder = 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keypackage com.cjs.example.bean;import org.springframework.jdbc.datasource.lookup.AbstractRoutingDataSource;import org.springframework.lang.Nullable;public class MyRoutingDataSource extends AbstractRoutingDataSource {@Nullable@Overrideprotected 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@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;@Servicepublic class MemberServiceImpl implements MemberService {@Autowiredprivate MemberMapper memberMapper;@Transactional@Overridepublic int insert(Member member) {return memberMapper.insert(member);}@Master@Overridepublic int save(Member member) {return memberMapper.insert(member);}@Overridepublic ListselectAll() {return memberMapper.selectByExample(new MemberExample());}@Master@Overridepublic 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;}}
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
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作者:Java思维导图
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