springboot2 + mybatis 多种方式实现多数据配置

     业务系统复杂程度增加，为了解决数据库I/O瓶颈，很自然会进行拆库拆表分服务来应对。这就会出现一个系统中可能会访问多处数据库，需要配置多个数据源。

第一种场景：项目服务从其它多处数据库取基础数据进行业务处理，因此各库之间不会出现重表等情况。

第二种场景：为了减轻写入压力进行读写分库，读走从库，写为主库。此种表名等信息皆为一致。

第三种场景：以上两种皆有。对于某些业务需要大数据量的汇总统计，希望不影响正常业务必须走从库（表信息一致），某些配置信息不存在读写压力，出现不分库（表信息不一致）

项目源代码：

https://github.com/zzsong/springboot-multiple-datasource.git

有三个目录：

one:
    直接使用多@Bean配置，@MapperScan来路径区分读何库
    
two:
    使用注解的方式来标识走何dataSource,AOP拦截注入动态数据源    

third:
    使用spring的Bean命名策略进行区分数据来源

项目技术选型： springBoot2.2.5 + mybatis + druid + mysql

先看主要的pom包

        <parent>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-parent</artifactId>
        <version>2.2.5.RELEASE</version>
        <relativePath/> 
    </parent>

                <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-data-jdbc</artifactId>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-data-jdbc</artifactId>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-aop</artifactId>
        </dependency>
        <dependency>
            <groupId>org.mybatis.spring.boot</groupId>
            <artifactId>mybatis-spring-boot-starter</artifactId>
            <version>2.1.2</version>
        </dependency>

        <dependency>
            <groupId>mysql</groupId>
            <artifactId>mysql-connector-java</artifactId>
            <version>8.0.19</version>
        </dependency>
        <dependency>
            <groupId>com.alibaba</groupId>
            <artifactId>druid-spring-boot-starter</artifactId>
            <version>1.1.21</version>
        </dependency>        

application.yml

spring:
  datasource:
    druid:
      core:
        url: jdbc:mysql:///kc_core?characterEncoding=utf-8&serverTimezone=Asia/Shanghai
        username: root
        password: 123456
        driver-class-name: com.mysql.cj.jdbc.Driver
        type: com.alibaba.druid.pool.DruidDataSource
      schedule:
        url: jdbc:mysql:///kc_schedule?characterEncoding=utf-8&serverTimezone=Asia/Shanghai
        username: root
        password: 123456
        driver-class-name: com.mysql.cj.jdbc.Driver
        type: com.alibaba.druid.pool.DruidDataSource

mysql新版本必须带有serverTimezone，不然会报连接异常。

第一种：通过@MapperScans 扫描匹配相关的数据源

@Configuration
@MapperScans({
        @MapperScan(basePackages = "com.zss.one.mapper.core", sqlSessionTemplateRef = "coreSqlSessionTemplate",sqlSessionFactoryRef = "coreSqlSessionFactory"),
        @MapperScan(basePackages = "com.zss.one.mapper.schedule", sqlSessionTemplateRef = "scheduleSqlSessionTemplate",sqlSessionFactoryRef = "scheduleSqlSessionFactory")
})
public class MybatisOneConfig {

    @Bean
    @ConfigurationProperties(prefix = "spring.datasource.druid.core")
    public DataSource coreDataSource(){
        return DruidDataSourceBuilder.create().build();
    }

    @Bean
    public SqlSessionFactory coreSqlSessionFactory(@Qualifier("coreDataSource") DataSource coreDataSource) throws Exception {
        SqlSessionFactoryBean sessionFactory = new SqlSessionFactoryBean();
        sessionFactory.setDataSource(coreDataSource);
        sessionFactory.getObject().getConfiguration().setJdbcTypeForNull(null);
        sessionFactory.getObject().getConfiguration().setMapUnderscoreToCamelCase(true);
        return sessionFactory.getObject();
    }

    @Bean
    public SqlSessionTemplate coreSqlSessionTemplate(@Qualifier("coreSqlSessionFactory") SqlSessionFactory sqlSessionFactory) throws Exception {
        return new SqlSessionTemplate(sqlSessionFactory);
    }

    //======schedule========
    @Bean
    @ConfigurationProperties(prefix = "spring.datasource.druid.schedule")
    public DataSource scheduleDataSource(){
        return DruidDataSourceBuilder.create().build();
    }

    @Bean
    public SqlSessionFactory scheduleSqlSessionFactory(@Qualifier("scheduleDataSource") DataSource coreDataSource) throws Exception {
        SqlSessionFactoryBean sessionFactory = new SqlSessionFactoryBean();
        sessionFactory.setDataSource(coreDataSource);
        sessionFactory.getObject().getConfiguration().setJdbcTypeForNull(null);
        sessionFactory.getObject().getConfiguration().setMapUnderscoreToCamelCase(true);
        return sessionFactory.getObject();
    }

    @Bean
    public SqlSessionTemplate scheduleSqlSessionTemplate(@Qualifier("scheduleSqlSessionFactory") SqlSessionFactory sqlSessionFactory) throws Exception {
        return new SqlSessionTemplate(sqlSessionFactory);
    }
}

第二种是动态数据源模式，通过AOP切入注解引导使用何数据源。用自定义注解@interface来标识方法走对应的数据源。

注意事项：类中的方法再调用带数据源的方法，不能被AOP切入

@Target({ElementType.METHOD, ElementType.TYPE})
@Retention(RetentionPolicy.RUNTIME)
@Documented
public @interface TargetDataSource {
    String value();
}

extends spring的动态DataSource路由来匹配

public class DynamicDataSource extends AbstractRoutingDataSource {

    @Override
    protected Object determineCurrentLookupKey() {
        return  DataSourceContextRouting.getDataSourceName();
    }
}

@Configuration
//@EnableConfigurationProperties(MybatisProperties.class)//不要使用此公共配置，Configuration会破坏相关dataSource的配置
@MapperScan("com.zss.two.mapper")
public class MybatisConfig {

    @Bean
    @ConfigurationProperties(prefix = "spring.datasource.druid.core")
    public DataSource coreDataSource() {
        return DruidDataSourceBuilder.create().build();
    }

    @Bean
    @ConfigurationProperties(prefix = "spring.datasource.druid.schedule")
    public DataSource scheduleDataSource() {
        return DruidDataSourceBuilder.create().build();
    }



    @Autowired
    @Qualifier("coreDataSource")
    private DataSource coreDataSource;

    @Autowired
    @Qualifier("scheduleDataSource")
    private DataSource scheduleDataSource;

    @Bean
    public DynamicDataSource dataSource() {
        Map<Object, Object> targetDataSources = new HashMap<>();
        targetDataSources.put(DataSourceConstants.CORE_DATA_SOURCE, coreDataSource);
        targetDataSources.put(DataSourceConstants.SCHEDULE_DATA_SOURCE, scheduleDataSource);

        DynamicDataSource dataSource = new DynamicDataSource();

        //设置数据源映射
        dataSource.setTargetDataSources(targetDataSources);
////        设置默认数据源，当无法映射到数据源时会使用默认数据源
        dataSource.setDefaultTargetDataSource(coreDataSource);
        dataSource.afterPropertiesSet();
        return dataSource;
    }
    /**
     * 根据数据源创建SqlSessionFactory
     */
    @Bean
    public SqlSessionFactory sqlSessionFactory(DynamicDataSource dataSource) throws Exception {
        SqlSessionFactoryBean sessionFactory = new SqlSessionFactoryBean();
        sessionFactory.setDataSource(dataSource);
        sessionFactory.getObject().getConfiguration().setJdbcTypeForNull(null);
        sessionFactory.getObject().getConfiguration().setMapUnderscoreToCamelCase(true);
        return sessionFactory.getObject();
    }

    @Bean
    public SqlSessionTemplate sqlSessionTemplate(SqlSessionFactory sqlSessionFactory) throws Exception {
        return new SqlSessionTemplate(sqlSessionFactory);
    }

第三种，自定义Bean命名策略，按beanName进行自动匹配使用数据源

@Component
public class CoreBeanNameGenerator implements BeanNameGenerator {
    @Override
    public String generateBeanName(BeanDefinition definition, BeanDefinitionRegistry registry) {
        return "core"+ ClassUtils.getShortName(definition.getBeanClassName());
    }
}


@Component
public class ScheduleBeanNameGenerator implements BeanNameGenerator {
    @Override
    public String generateBeanName(BeanDefinition definition, BeanDefinitionRegistry registry) {
        return "schedule"+ ClassUtils.getShortName(definition.getBeanClassName());
    }
}

使用mybatis MapperScannerConfigurer自动扫描，将Mapper接口生成注入到spring

    @Bean
    public MapperScannerConfigurer coreMapperScannerConfig(CoreBeanNameGenerator coreBeanNameGenerator){
        MapperScannerConfigurer configurer = new MapperScannerConfigurer();
        configurer.setNameGenerator(coreBeanNameGenerator);
        configurer.setBasePackage("com.zss.third.mapper.core,com.zss.third.mapper.order");
        configurer.setSqlSessionFactoryBeanName("coreSqlSessionFactory");
        configurer.setSqlSessionTemplateBeanName("coreSqlSessionTemplate");
        return configurer;
    }



    @Bean
    public MapperScannerConfigurer scheduleMapperScannerConfig(ScheduleBeanNameGenerator scheduleBeanNameGenerator){
        MapperScannerConfigurer configurer = new MapperScannerConfigurer();
        configurer.setNameGenerator(scheduleBeanNameGenerator);
        configurer.setBasePackage("com.zss.third.mapper.schedule,com.zss.third.mapper.order");
        configurer.setSqlSessionFactoryBeanName("scheduleSqlSessionFactory");
        configurer.setSqlSessionTemplateBeanName("scheduleSqlSessionTemplate");
        return configurer;
    }

到此，三种多数据源匹配主要点介绍完，详细直接下载github项目。 在resources/db含有相关测试表及数据脚本。