Mybatis引出的一系列问题-spring多数据源配置-编程知识

在日常开发中我们都是以单个数据库进行开发，在小型项目中是完全能够满足需求的。但是，当我们牵扯到像淘宝、京东这样的大型项目的时候，单个数据库就难以承受用户的CRUD操作。那么此时，我们就需要使用多个数据源进行读写分离的操作，这种方式也是目前一种流行的数据管理方式。

1 Spring Boot配置多数据源

在YAML文件中定义数据源所需的数据：

spring:datasource:type: com.alibaba.druid.pool.DruidDataSourcedefault-datasource:username: rootpassword: rooturl: jdbc:mysql://localhost:3306/default?serverTimezone=UTC&useUnicode=true&characterEncoding=utf-8driver-class-name: com.mysql.jdbc.Driverinspur-zs-datasource:username: rootpassword: rooturl: jdbc:mysql://localhost:3306/inspur-zs?serverTimezone=UTC&useUnicode=true&characterEncoding=utf-8driver-class-name: com.mysql.jdbc.Driverdruid:initial-size: 5min-idle: 1max-active: 20profiles:active: devmybatis:mapper-locations: classpath:/mapper/*.xmltype-aliases-package: com.inspur.pojoconfiguration:mapUnderscoreToCamelCase: truelog-impl: org.apache.ibatis.logging.slf4j.Slf4jImpl

定义多个数据源：

package com.inspur.spring.config.datasource;import com.alibaba.druid.spring.boot.autoconfigure.DruidDataSourceBuilder;
import org.springframework.boot.context.properties.ConfigurationProperties;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;import javax.sql.DataSource;/*** 数据源配置* ConfigurationProperties注解用于将YAML中指定的数据创建成指定的对象，* 但是，YAML中的数据必须要与对象对象中的属性同名，不然无法由Spring Boot完成赋值。** @author zhaoshuai-lc* @date 2023/07/11*/
@Configuration
public class DataSourceConfig {@Bean(name = "defaultDatasource")@ConfigurationProperties(prefix = "spring.datasource.default-datasource")public DataSource defaultDatasource() {return DruidDataSourceBuilder.create().build();}@Bean(name = "inspurZsDatasource")@ConfigurationProperties(prefix = "spring.datasource.inspur-zs-datasource")public DataSource inspurZsDatasource() {return DruidDataSourceBuilder.create().build();}
}

由于我们要定义多个数据源，所以在Spring Boot数据源自动配置类中就无法确定导入哪个数据源来完成初始化，所以我们就需要禁用掉Spring Boot的数据源自动配置类，然后使用我们自定义的数据源配置类来完成数据源的初始化与管理。

package com.inspur;import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.boot.autoconfigure.jdbc.DataSourceAutoConfiguration;
import org.springframework.context.annotation.EnableAspectJAutoProxy;/*** WtMybatisStudyApplication* 由于我们要定义多个数据源，所以在Spring Boot数据源自动配置类中就无法确定导入哪个数据源来完成初始化，* 所以我们就需要禁用掉Spring Boot的数据源自动配置类，然后使用我们自定义的数据源配置类来完成数据源的初始化与管理。** @author zhaoshuai-lc* @date 2023/07/11*/
@SpringBootApplication(exclude = {DataSourceAutoConfiguration.class})
@EnableAspectJAutoProxy
public class WtMybatisStudyApplication {public static void main(String[] args) {SpringApplication.run(WtMybatisStudyApplication.class, args);}
}

1.1 指定数据源-实现DataSource接口

缺点：产生大量的代码冗余，在代码中存在硬编码。

package com.inspur.spring.config.datasource;import org.springframework.context.annotation.Primary;
import org.springframework.stereotype.Component;import javax.annotation.Resource;
import javax.sql.DataSource;
import java.io.PrintWriter;
import java.sql.Connection;
import java.sql.SQLException;
import java.sql.SQLFeatureNotSupportedException;
import java.util.logging.Logger;/*** 方式一* DynamicDataSource1* 实现DataSource接口我们本质上只使用了一个方法就是getConnection()这个无参的方法** @author zhaoshuai-lc* @date 2023/07/11*/
@Component
@Primary
public class DynamicDataSource1 implements DataSource {public static ThreadLocal<String> flag = new ThreadLocal<>();@Resourceprivate DataSource defaultDatasource;@Resourceprivate DataSource inspurZsDatasource;public DynamicDataSource1() {flag.set("defaultDatasource");}@Overridepublic Connection getConnection() throws SQLException {if (flag.get().equals("defaultDatasource")) {return defaultDatasource.getConnection();} else if (flag.get().equals("inspurZsDatasource")) {return inspurZsDatasource.getConnection();}return defaultDatasource.getConnection();}@Overridepublic Connection getConnection(String username, String password) throws SQLException {return null;}@Overridepublic <T> T unwrap(Class<T> iface) throws SQLException {return null;}@Overridepublic boolean isWrapperFor(Class<?> iface) throws SQLException {return false;}@Overridepublic PrintWriter getLogWriter() throws SQLException {return null;}@Overridepublic void setLogWriter(PrintWriter out) throws SQLException {}@Overridepublic void setLoginTimeout(int seconds) throws SQLException {}@Overridepublic int getLoginTimeout() throws SQLException {return 0;}@Overridepublic Logger getParentLogger() throws SQLFeatureNotSupportedException {return null;}
}

实现DataSource接口我们本质上只使用了一个方法，就是getConnection()这个无参的方法，但是DataSource接口中所有的方法我们也都需要实现，只是不用写方法体而已，也就是存在了很多的 “废方法” 。
@Primary注解 == @Order(1)，用于设置此类的注入顺序。

使用：

    @Overridepublic PageData<BsFactoryCalendar> selectByExample(BsFactoryCalendarExample example) {PageData<BsFactoryCalendar> pageData = new PageData<>();DynamicDataSource1.flag.set("default-datasource");List<BsFactoryCalendar> bsFactoryCalendars = bsFactoryCalendarMapper.selectByExample(example);PageInfo<BsFactoryCalendar> pageInfo = new PageInfo<>(bsFactoryCalendars);pageData.setRows(bsFactoryCalendars);pageData.setTotal(pageInfo.getTotal());return pageData;}

1.2 指定数据源-继承AbstrictRoutingDataSource类

减少了代码的冗余，但是还是会存在硬编码。

package com.inspur.spring.config.datasource;import cn.hutool.core.map.MapUtil;
import org.springframework.context.annotation.Primary;
import org.springframework.jdbc.datasource.lookup.AbstractRoutingDataSource;
import org.springframework.stereotype.Component;import javax.annotation.Resource;
import javax.sql.DataSource;
import java.util.Map;/*** DynamicDataSource2* AbstrictRoutingDataSource的本质就是利用一个Map将数据源存储起来，然后通过Key来得到Value来修改数据源。** @author zhaoshuai-lc* @date 2023/07/11*/@Component
@Primary
public class DynamicDataSource2 extends AbstractRoutingDataSource {public static ThreadLocal<String> flag = new ThreadLocal<>();@Resourceprivate DataSource defaultDatasource;@Resourceprivate DataSource inspurZsDatasource;public DynamicDataSource2() {flag.set("defaultDatasource");}@Overrideprotected Object determineCurrentLookupKey() {return flag.get();}@Overridepublic void afterPropertiesSet() {Map<Object, Object> targetDataSource = MapUtil.newConcurrentHashMap();// 将第一个数据源设置为默认的数据源super.setDefaultTargetDataSource(defaultDatasource);targetDataSource.put("defaultDatasource", defaultDatasource);targetDataSource.put("inspurZsDatasource", inspurZsDatasource);super.setTargetDataSources(targetDataSource);super.afterPropertiesSet();}
}

AbstrictRoutingDataSource的本质就是利用一个Map将数据源存储起来，然后通过Key来得到Value来修改数据源。

使用：

    @Overridepublic PageData<BsFactoryCalendar> selectByExample(BsFactoryCalendarExample example) {PageData<BsFactoryCalendar> pageData = new PageData<>();DynamicDataSource2.flag.set("default-datasource");List<BsFactoryCalendar> bsFactoryCalendars = bsFactoryCalendarMapper.selectByExample(example);PageInfo<BsFactoryCalendar> pageInfo = new PageInfo<>(bsFactoryCalendars);pageData.setRows(bsFactoryCalendars);pageData.setTotal(pageInfo.getTotal());return pageData;}

1.3 指定数据源-使用Spring AOP + 自定义注解的形式

Spring AOP + 自定义注解的形式是一种推荐的写法，减少代码的冗余且不存在硬编码。此方法适合对指定功能操作指定数据库的模式。

导入依赖：

<dependency><groupId>org.springframework.boot</groupId><artifactId>spring-boot-starter-aop</artifactId>
</dependency>

开启AOP支持：

package com.inspur;import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.boot.autoconfigure.jdbc.DataSourceAutoConfiguration;
import org.springframework.context.annotation.EnableAspectJAutoProxy;@SpringBootApplication(exclude = {DataSourceAutoConfiguration.class})
@EnableAspectJAutoProxy
public class WtMybatisStudyApplication {public static void main(String[] args) {SpringApplication.run(WtMybatisStudyApplication.class, args);}}

定义枚举来表示数据源的标识：

package com.inspur.spring.config.datasource.enums;public enum DataSourceType {DEFAULT_DATASOURCE,INSPURZS_DATASOURCE,
}

继承AbstractRoutingDataSource类：

package com.inspur.spring.config.datasource;import cn.hutool.core.map.MapUtil;
import com.inspur.spring.config.datasource.enums.DataSourceType;
import org.springframework.context.annotation.Primary;
import org.springframework.jdbc.datasource.lookup.AbstractRoutingDataSource;
import org.springframework.stereotype.Component;import javax.annotation.Resource;
import javax.sql.DataSource;
import java.util.Map;@Primary
@Component
public class DynamicDataSource3 extends AbstractRoutingDataSource {public static ThreadLocal<String> flag = new ThreadLocal<>();@Resourceprivate DataSource defaultDatasource;@Resourceprivate DataSource inspurZsDatasource;public DynamicDataSource3() {flag.set(DataSourceType.DEFAULT_DATASOURCE.name());}@Overrideprotected Object determineCurrentLookupKey() {return flag.get();}@Overridepublic void afterPropertiesSet() {Map<Object, Object> targetDataSource = MapUtil.newConcurrentHashMap();// 将第一个数据源设置为默认的数据源super.setDefaultTargetDataSource(defaultDatasource);targetDataSource.put(DataSourceType.DEFAULT_DATASOURCE.name(), defaultDatasource);targetDataSource.put(DataSourceType.INSPURZS_DATASOURCE.name(), inspurZsDatasource);super.setTargetDataSources(targetDataSource);super.afterPropertiesSet();}
}

自定义注解：

package com.inspur.spring.config.datasource.annotation;import com.inspur.spring.config.datasource.enums.DataSourceType;import java.lang.annotation.Documented;
import java.lang.annotation.ElementType;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;@Target({ElementType.TYPE, ElementType.METHOD})
@Retention(RetentionPolicy.RUNTIME)
@Documented
public @interface TargetDataSource {DataSourceType value() default DataSourceType.DEFAULT_DATASOURCE;
}

定义注解的实现类：

package com.inspur.spring.config.datasource.annotation;import com.inspur.spring.config.datasource.DynamicDataSource3;
import lombok.extern.slf4j.Slf4j;
import org.aspectj.lang.JoinPoint;
import org.aspectj.lang.annotation.Aspect;
import org.aspectj.lang.annotation.Before;
import org.aspectj.lang.reflect.MethodSignature;
import org.springframework.stereotype.Component;import java.lang.reflect.Method;/*** TargetDataSourceAspect** @author zhaoshuai-lc* @date 2023/07/11*/
@Component
@Aspect
@Slf4j
public class TargetDataSourceAspect {@Before("@within(com.inspur.spring.config.datasource.annotation.TargetDataSource) || " +"@annotation(com.inspur.spring.config.datasource.annotation.TargetDataSource)")public void beforeNoticeUpdateDataSource(JoinPoint joinPoint) {TargetDataSource annotation = null;Class<? extends Object> target = joinPoint.getTarget().getClass();if (target.isAnnotationPresent(TargetDataSource.class)) {// 判断类上是否标注着注解annotation = target.getAnnotation(TargetDataSource.class);log.info("类: {}, 标注了注解@TargetDataSource", target);} else {Method method = ((MethodSignature) joinPoint.getSignature()).getMethod();if (method.isAnnotationPresent(TargetDataSource.class)) {// 判断方法上是否标注着注解，如果类和方法上都没有标注，则报错annotation = method.getAnnotation(TargetDataSource.class);log.info("方法: {}, 标注了注解@TargetDataSource", method);} else {log.error("注解@TargetDataSource只能用于类或者方法上, error: {} {}", target, method);throw new RuntimeException("注解@TargetDataSource使用错误");}}// 切换数据源DynamicDataSource3.flag.set(annotation.value().name());}
}

使用：

package com.inspur.spring.service;import com.github.pagehelper.PageInfo;
import com.inspur.spring.common.interfaceResult.PageData;
import com.inspur.spring.config.datasource.annotation.TargetDataSource;
import com.inspur.spring.config.datasource.enums.DataSourceType;
import com.inspur.spring.dao.BsFactoryCalendarMapper;
import com.inspur.spring.pojo.BsFactoryCalendar;
import com.inspur.spring.pojo.BsFactoryCalendarExample;
import org.springframework.stereotype.Service;
import org.springframework.transaction.annotation.Transactional;import javax.annotation.Resource;
import java.util.List;@Service
@TargetDataSource(value = DataSourceType.DEFAULT_DATASOURCE) // 方式三 多数据源设置
public class BsFactoryCalendarServiceImpl implements BsFactoryCalendarService {@Resourceprivate BsFactoryCalendarMapper bsFactoryCalendarMapper;@Override@Transactionalpublic PageData<BsFactoryCalendar> selectByExample(BsFactoryCalendarExample example) {PageData<BsFactoryCalendar> pageData = new PageData<>();List<BsFactoryCalendar> bsFactoryCalendars = bsFactoryCalendarMapper.selectByExample(example);PageInfo<BsFactoryCalendar> pageInfo = new PageInfo<>(bsFactoryCalendars);pageData.setRows(bsFactoryCalendars);pageData.setTotal(pageInfo.getTotal());return pageData;}
}

1.4 通过SqlSessionFactory指定的数据源来操作指定目录的XML文件

使用此方法则不会与上面所述的类有任何关系，本方法会重新定义类。本方法也是一种推荐的方法，适用于对指定数据库的操作，也就是适合读写分离。不会存在代码冗余和存在硬编码。

在这里插入图片描述

配置YAML文件：

spring:datasource:type: com.alibaba.druid.pool.DruidDataSourcedefault-datasource:username: rootpassword: rootjdbc-url: jdbc:mysql://localhost:3306/default?serverTimezone=UTC&useUnicode=true&characterEncoding=utf-8driver-class-name: com.mysql.jdbc.Driverinspur-zs-datasource:username: rootpassword: rootjdbc-url: jdbc:mysql://localhost:3306/inspur-zs?serverTimezone=UTC&useUnicode=true&characterEncoding=utf-8driver-class-name: com.mysql.jdbc.Drivermain:allow-bean-definition-overriding : truedruid:initial-size: 5min-idle: 1max-active: 20profiles:active: devmybatis:mapper-locations: classpath:/mapper/*.xmltype-aliases-package: com.inspur.pojoconfiguration:mapUnderscoreToCamelCase: truelog-impl: org.apache.ibatis.logging.slf4j.Slf4jImpl

针对Mapper层通过SqlSessionFactory指定数据源来操作：

package com.inspur.spring.config.datasource;import org.apache.ibatis.session.SqlSessionFactory;
import org.mybatis.spring.SqlSessionFactoryBean;
import org.mybatis.spring.SqlSessionTemplate;
import org.mybatis.spring.annotation.MapperScan;
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 org.springframework.context.annotation.Primary;
import org.springframework.core.io.support.PathMatchingResourcePatternResolver;
import org.springframework.jdbc.datasource.DataSourceTransactionManager;
import org.springframework.transaction.PlatformTransactionManager;import javax.sql.DataSource;@Configuration
@MapperScan(basePackages = "com.inspur.spring.dao.defaultzs", sqlSessionFactoryRef = "DefaultSqlSessionFactory")
public class DefaultDatasourceConfig {@Primary@Bean(name = "DefaultDatasource")@ConfigurationProperties(prefix = "spring.datasource.default-datasource")public DataSource getDateSource1() {return DataSourceBuilder.create().build();}@Primary@Bean(name = "DefaultSqlSessionFactory")public SqlSessionFactory sqlSessionFactory(@Qualifier("DefaultDatasource") DataSource datasource) throws Exception {SqlSessionFactoryBean bean = new SqlSessionFactoryBean();bean.setDataSource(datasource);// 设置mybatis的xml所在位置bean.setMapperLocations(new PathMatchingResourcePatternResolver().getResources("classpath*:mapper/defaultzs/*.xml"));return bean.getObject();}@Bean("DefaultSqlSessionTemplate")@Primarypublic SqlSessionTemplate sqlSessionTemplate(@Qualifier("DefaultSqlSessionFactory") SqlSessionFactory factory) {return new SqlSessionTemplate(factory);}@Beanpublic PlatformTransactionManager transactionManager(@Qualifier("DefaultDatasource") DataSource dataSource) {return new DataSourceTransactionManager(dataSource);}
}

package com.inspur.spring.config.datasource;import org.apache.ibatis.session.SqlSessionFactory;
import org.mybatis.spring.SqlSessionFactoryBean;
import org.mybatis.spring.SqlSessionTemplate;
import org.mybatis.spring.annotation.MapperScan;
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 org.springframework.context.annotation.Primary;
import org.springframework.core.io.support.PathMatchingResourcePatternResolver;
import org.springframework.jdbc.datasource.DataSourceTransactionManager;
import org.springframework.transaction.PlatformTransactionManager;import javax.sql.DataSource;@Configuration
@MapperScan(basePackages = "com.inspur.spring.dao.inspurzs", sqlSessionFactoryRef = "InspurZsSqlSessionFactory")
public class InspurZsDatasourceConfig {@Primary@Bean(value = "InspurZsDatasource")@ConfigurationProperties(prefix = "spring.datasource.inspur-zs-datasource")public DataSource getDateSource1() {return DataSourceBuilder.create().build();}@Primary@Bean(value = "InspurZsSqlSessionFactory")public SqlSessionFactory sqlSessionFactory(@Qualifier("InspurZsDatasource") DataSource datasource) throws Exception {SqlSessionFactoryBean bean = new SqlSessionFactoryBean();bean.setDataSource(datasource);// 设置mybatis的xml所在位置bean.setMapperLocations(new PathMatchingResourcePatternResolver().getResources("classpath*:mapper/inspurzs/*.xml"));return bean.getObject();}@Bean(value = "InspurZsSqlSessionTemplate")@Primarypublic SqlSessionTemplate sqlSessionTemplate(@Qualifier("InspurZsSqlSessionFactory") SqlSessionFactory factory) {return new SqlSessionTemplate(factory);}@Beanpublic PlatformTransactionManager transactionManager(@Qualifier("InspurZsDatasource") DataSource dataSource) {return new DataSourceTransactionManager(dataSource);}
}

@MapperScan注解中的basePackages指向的是指定的Dao层。
@MapperScan注解中sqlSessionFactoryRef 用来指定使用某个SqlSessionFactory来操作数据源。

 bean.setMapperLocations(new PathMatchingResourcePatternResolver().getResources("classpath*:mapper/inspurzs/*.xml"));

使用此种方法不会存在任何代码的冗余以及硬编码的存在，但是需要分层明确。唯一的不足就是添加一个数据源就需要重新写一个类，而这个类中的代码大部分又是相同的。