Spring boot JPA如何从同一连接添加多个数据库？

# 数据源1
spring.datasource.db1.url=jdbc:mysql://localhost:3306/db1
spring.datasource.db1.username=root
spring.datasource.db1.password=123456
spring.datasource.db1.driver-class-name=com.mysql.jdbc.Driver

# 数据源2
spring.datasource.db2.url=jdbc:mysql://localhost:3306/db2
spring.datasource.db2.username=root
spring.datasource.db2.password=123456
spring.datasource.db2.driver-class-name=com.mysql.jdbc.Driver

@Configuration
public class DB1Config {

    @Bean
    @ConfigurationProperties("spring.datasource.db1")
    public DataSourceProperties db1DataSourceProperties() {
        return new DataSourceProperties();
    }

    @Bean
    @ConfigurationProperties("spring.datasource.db1")
    public DataSource db1DataSource() {
        return db1DataSourceProperties().initializeDataSourceBuilder().build();
    }

    @Bean
    public LocalContainerEntityManagerFactoryBean db1EntityManagerFactory(EntityManagerFactoryBuilder builder) {
        return builder
                .dataSource(db1DataSource())
                .packages("com.example.db1.entity")
                .persistenceUnit("db1")
                .build();
    }

    @Bean
    public PlatformTransactionManager db1TransactionManager(EntityManagerFactoryBuilder builder) {
        return new JpaTransactionManager(db1EntityManagerFactory(builder).getObject());
    }
}

@Configuration
public class DB2Config {

    @Bean
    @ConfigurationProperties("spring.datasource.db2")
    public DataSourceProperties db2DataSourceProperties() {
        return new DataSourceProperties();
    }

    @Bean
    @ConfigurationProperties("spring.datasource.db2")
    public DataSource db2DataSource() {
        return db2DataSourceProperties().initializeDataSourceBuilder().build();
    }

    @Bean
    public LocalContainerEntityManagerFactoryBean db2EntityManagerFactory(EntityManagerFactoryBuilder builder) {
        return builder
                .dataSource(db2DataSource())
                .packages("com.example.db2.entity")
                .persistenceUnit("db2")
                .build();
    }

    @Bean
    public PlatformTransactionManager db2TransactionManager(EntityManagerFactoryBuilder builder) {
        return new JpaTransactionManager(db2EntityManagerFactory(builder).getObject());
    }
}

@Repository
public class UserRepository {

    @PersistenceContext(unitName = "db1")
    private EntityManager entityManager;

    // ...
}