Driver.java

import org.springframework.aop.target.HotSwappableTargetSource;
import org.springframework.context.ApplicationContext;
import org.springframework.context.support.GenericXmlApplicationContext;

/**
 * Inspired by: https://stackoverflow.com/a/12808171/154461
 */
public class SwappableBeans {
    public static void main(String... args) {

        ApplicationContext ctx = new GenericXmlApplicationContext("swappableBeans.xml");

        Person personFromXml = (Person) ctx.getBean("personFromXml");
        System.out.println(String.format("personFromXml: Hello '%s', age '%s'", personFromXml.getName(), personFromXml.getAge()));

        Person personProxy = (Person) ctx.getBean("personProxy");
        System.out.println(String.format("personProxy: Hello '%s', age '%s'", personProxy.getName(), personProxy.getAge()));

        Person lori = new Person("Lori", 49);

        HotSwappableTargetSource personSwapper = (HotSwappableTargetSource) ctx.getBean("personSwapper");
        Person previousPerson = (Person) personSwapper.swap(lori);
        System.out.println(String.format("previousPerson: Hello '%s', age '%s'", previousPerson.getName(), previousPerson.getAge()));

        personFromXml = (Person) ctx.getBean("personFromXml");
        System.out.println(String.format("personFromXml: Hello '%s', age '%s'. Still same!", personFromXml.getName(), personFromXml.getAge()));

        personProxy = (Person) ctx.getBean("personProxy");
        System.out.println(String.format("personProxy: Hello '%s', age '%s'.  Was swapped!", personProxy.getName(), personProxy.getAge()));

        /** OUTPUT:
         * personFromXml: Hello 'Tim', age '46'
         * personProxy: Hello 'Tim', age '46'
         * previousPerson: Hello 'Tim', age '46'
         * personFromXml: Hello 'Tim', age '46'. Still same!
         * personProxy: Hello 'Lori', age '49'.  Was swapped!
         */
    } // end main
} // end class

Person.java

public class Person {
    private String name;
    private Integer age;

    public Person(String name, Integer age) {
        this.name = name;
        this.age = age;
    }

    public String getName() {
        return name;
    }

    public Integer getAge() {
        return age;
    }
}

swappableBeans.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"
       xsi:schemaLocation="http://www.springframework.org/schema/beans
   http://www.springframework.org/schema/beans/spring-beans-3.0.xsd">

    <!--https://stackoverflow.com/questions/12800769/replace-spring-bean-in-one-context-with-mock-version-from-another-context-->
    <bean id="personFromXml" class="harschware.sandbox.Person">
        <constructor-arg index="0" value="Tim"/>
        <constructor-arg index="1" type="java.lang.Integer" value="46"/>
    </bean>

    <bean id="personSwapper" class="org.springframework.aop.target.HotSwappableTargetSource">
        <constructor-arg ref="personFromXml"/>
    </bean>

    <bean id="personProxy" class="org.springframework.aop.framework.ProxyFactoryBean">
        <property name="targetSource" ref="personSwapper"/>
    </bean>
</beans>