如何配置以实现对多个数据库的同时访问？

在配置同时访问多个数据库时，可以通过以下步骤实现：

1、添加依赖

在项目的pom.xml文件中添加相关依赖，确保项目能够支持多数据源的配置，使用Spring Boot和MyBatis时，需要引入如下依赖：

     <dependency>
         <groupId>mysql</groupId>
         <artifactId>mysql-connector-java</artifactId>
         <scope>runtime</scope>
     </dependency>
     <dependency>
         <groupId>org.springframework.boot</groupId>
         <artifactId>spring-boot-starter-jdbc</artifactId>
     </dependency>
     <dependency>
         <groupId>org.mybatis</groupId>
         <artifactId>mybatis</artifactId>
         <version>3.5.5</version>
     </dependency>
     <dependency>
         <groupId>com.alibaba</groupId>
         <artifactId>druid</artifactId>
         <version>1.2.3</version>
     </dependency>
     <dependency>
         <groupId>org.mybatis</groupId>
         <artifactId>mybatis-spring</artifactId>
         <version>2.0.7</version>
     </dependency>
     <dependency>
         <groupId>org.projectlombok</groupId>
         <artifactId>lombok</artifactId>
         <optional>true</optional>
     </dependency>

2、配置文件

在application.yml或application.properties中配置多个数据源的信息，假设有两个数据库test_db和biztest_db，其配置如下：

     spring:
       datasource:
         dev:
           driver-class-name: com.mysql.cj.jdbc.Driver
           jdbcUrl: jdbc:mysql://localhost:3306/test_db?useSSL=false&useUnicode=true&characterEncoding=UTF-8&serverTimezone=GMT%2B8
           username: root
           password: 123456
           type: com.alibaba.druid.pool.DruidDataSource
         local:
           driver-class-name: com.mysql.cj.jdbc.Driver
           jdbcUrl: jdbc:mysql://localhost:3306/biztest_db?useSSL=false&useUnicode=true&characterEncoding=UTF-8&serverTimezone=GMT%2B8
           username: biz_rw
           password: 654321
           type: com.alibaba.druid.pool.DruidDataSource

3、创建配置类

为每个数据源创建一个配置类，用于生成相应的DataSource和SqlSessionFactory对象。

     @Configuration
     @MapperScan(basePackages = "com.yourcom.proname.repository.mapper.dev", sqlSessionFactoryRef = "devSqlSessionFactory")
     public class DevDataSourceConfig {
         @Primary
         @Bean(name = "devDataSource")
         @ConfigurationProperties("spring.datasource.dev")
         public DataSource masterDataSource() {
             return DruidDataSourceBuilder.create().build();
         }
         @Primary
         @Bean(name = "devTransactionManager")
         public DataSourceTransactionManager masterTransactionManager(@Qualifier("devDataSource") DataSource dataSource) {
             return new DataSourceTransactionManager(dataSource);
         }
         @Primary
         @Bean(name = "devSqlSessionFactory")
         @ConfigurationPropertiesBinding
         public SqlSessionFactory sqlSessionFactory(@Qualifier("devDataSource") DataSource dataSource) throws Exception {
             MybatisSqlSessionFactoryBean factoryBean = new MybatisSqlSessionFactoryBean();
             factoryBean.setDataSource(dataSource);
             return factoryBean.getObject();
         }
     }
     @Configuration
     @MapperScan(basePackages = "com.yourcom.proname.repository.mapper.local", sqlSessionFactoryRef = "localSqlSessionFactory")
     public class LocalDataSourceConfig {
         @Bean(name = "localDataSource")
         @ConfigurationProperties("spring.datasource.local")
         public DataSource druidDataSource() {
             return DruidDataSourceBuilder.create().build();
         }
         @Bean(name = "localTransactionManager")
         public DataSourceTransactionManager masterTransactionManager(@Qualifier("localDataSource") DataSource dataSource) {
             return new DataSourceTransactionManager(dataSource);
         }
         @Bean(name = "localSqlSessionFactory")
         public SqlSessionFactory sqlSessionFactory(@Qualifier("localDataSource") DataSource dataSource) throws Exception {
             MybatisSqlSessionFactoryBean factoryBean = new MybatisSqlSessionFactoryBean();
             factoryBean.setDataSource(dataSource);
             return factoryBean.getObject();
         }
     }