Multiple data sources in one project

I am working on a java project in which I have to store some data in a database or another according to a value in a variable. For the management of BBDD I use myBatis.

The configuration to the DBs:

context.xml

<?xml version="1.0" encoding="UTF-8"?>
<Context path="/pathApp" reloadable="true">
    <Resource auth="Container" driverClassName="oracle.jdbc.OracleDriver" maxIdle="1" maxTotal="20" maxWaitMillis="-1" name="jdbc/DB1" password="pass1" removeAbandonedOnBorrow="true" removeAbandonedTimeout="60" type="javax.sql.DataSource" url="ulrBD1" username="usernameDB1"/>
    <Resource auth="Container" driverClassName="oracle.jdbc.OracleDriver" maxIdle="1" maxTotal="20" maxWaitMillis="-1" name="jdbc/DB2" password="pass2" removeAbandonedOnBorrow="true" removeAbandonedTimeout="60" type="javax.sql.DataSource" url="urlDB2" username="usernameDB2"/>
</Context>

context-dfg.xml

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xmlns:context="http://www.springframework.org/schema/context"
    xmlns:tx="http://www.springframework.org/schema/tx"
    xsi:schemaLocation="
   http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans-3.0.xsd
   http://www.springframework.org/schema/context http://www.springframework.org/schema/context/spring-context-3.0.xsd
   http://www.springframework.org/schema/tx http://www.springframework.org/schema/tx/spring-tx-3.0.xsd">

<context:component-scan base-package="com.nombreCompañia.ajax.service" />

<context:annotation-config />

<bean id="dataSource" class="org.springframework.jndi.JndiObjectFactoryBean">
    <property name="jndiName">
        <value>java:comp/env/jdbc/DB1</value>
    </property>
</bean>

<bean id="transactionManager" class="org.springframework.jdbc.datasource.DataSourceTransactionManager">
    <property name="dataSource" ref="dataSource" />
</bean>

   <bean id="dataSource_DB2" class="org.springframework.jndi.JndiObjectFactoryBean">
    <property name="jndiName">
        <value>java:comp/env/jdbc/DB2</value>
    </property>
</bean>

<bean id="transactionManager_DB2" class="org.springframework.jdbc.datasource.DataSourceTransactionManager">
    <property name="dataSource" ref="dataSource_DB2" />
</bean>

<tx:annotation-driven />

<bean id="sqlSessionFactory" class="org.mybatis.spring.SqlSessionFactoryBean">
    <property name="dataSource" ref="dataSource" />
</bean>

<bean id="sqlSessionFactory_DB2" class="org.mybatis.spring.SqlSessionFactoryBean">
    <property name="dataSource" ref="dataSource_DB2" />
</bean>

<bean class="org.mybatis.spring.mapper.MapperScannerConfigurer">
    <property name="basePackage" value="com.iberdrola.persistence.dao" />
    <property name="sqlSessionFactory" ref="sqlSessionFactory" />
</bean>   

I declare the resources in web.xml

<resource-ref id="ResourceRef_5">
    <description>Base de datos 1</description>
    <res-ref-name>jdbc/DB1</res-ref-name>
    <res-type>javax.sql.DataSource</res-type>
    <res-auth>Container</res-auth>
    <res-sharing-scope>Shareable</res-sharing-scope>
</resource-ref>

<resource-ref id="ResourceRef_0">
    <description>Base de datos 2</description>
    <res-ref-name>jdbc/DB2</res-ref-name>
    <res-type>javax.sql.DataSource</res-type>
    <res-auth>Container</res-auth>
    <res-sharing-scope>Shareable</res-sharing-scope>
</resource-ref>

I have it this way because for database 1 I have not had any problems and it works correctly, so I decided to duplicate the configuration for the second DB, modifying its own configuration.

But how do I change at runtime to use one database or another?

I've searched a lot on the internet and I can't find a solution.

I hope your help.

Thank you