Spring AOP - Changing target of a Proxy at runtime

I had a pretty strange usecase where i wanted to change the target object of the proxy and runtime. Spring makes it so simple to use.

My usecase was as follows

      ApplicationContext ctx = new ClassPathXmlApplicationContext(
                "classpath:META-INF/spring/aop-poc-module-context.xml");
        AccountDAO accountDao = (AccountDAO) ctx.getBean("accountDao");

        IAccount account = accountDao.getById(123);

        System.out.println("account" + account);

        account.setName("sudheer");

        System.out.println("account" + account);

Is a property is change on the entity , i want to change the entity object itself , that is , in the above use two sysouts will print different objects.

The use case arose because i was using a cache(infinispan) which did not allow modifying POJOs outside a transaction scope.

I did achieve the same using the follwing

public class AccountDAO {

    private Advisor advisor;

    //This is get methods of the accountDao

    public IAccount getById(long id) {
        //creating new account - to mock database behavior
        IAccount a = new Account(369, "suji");
       //Using spring factory
        ProxyFactory pf = new ProxyFactory();
        pf.setExposeProxy(true);
        pf.addInterface(IAccount.class);
       //Using by own Target source to change the Target
        pf.setTargetSource(new SwappableTargetSource(a));
       //advisor which holds the advice and pointcut
        pf.addAdvisor(advisor);
        return (IAccount) pf.getProxy();
    }

 public void setAdvisor(Advisor advisor) {
        this.advisor = advisor;
    }

}

My advice class

public class SwappableBeforeAdvice implements MethodBeforeAdvice {

    @Override
    public void before(Method method, Object[] args, Object target)
            throws Throwable {
        System.out.println("Before advice called");

        if (!((IAccount) target).isWritable()) {

   //Changing the target source based on specific business condition
            ((SwappableTargetSource) ((Advised) AopContext.currentProxy())
                    .getTargetSource()).swap(new Account(56, "dan"));
        }

    }
}

My custom target source

public class SwappableTargetSource implements TargetSource {

    private Object target;

    public SwappableTargetSource(Object initialTarget) {
        this.target = initialTarget;
    }

    public synchronized Class<?> getTargetClass() {
        return this.target.getClass();
    }

    public final boolean isStatic() {
        return false;
    }

    public synchronized Object getTarget() {
        return this.target;
    }

    public void releaseTarget(Object target) {
        // nothing to do
    }

    public synchronized void swap(Object newTarget)
            throws IllegalArgumentException {
        this.target = newTarget;
    }

    @Override
    public boolean equals(Object other) {
        return (this == other || (other instanceof SwappableTargetSource && this.target
                .equals(((SwappableTargetSource) other).target)));
    }

    @Override
    public int hashCode() {
        return SwappableTargetSource.class.hashCode();
    }

    @Override
    public String toString() {
        return "SwappableTargetSource for target: " + this.target;
    }

}

These are the spring xml configuration.

<bean id="accountDao" class="com.test.dao.account.AccountDAO">
         <property name="advisor" ref="settersAdvisor" />
    </bean>

    <bean id="swapableBeforeAdvice" class="com.test.framework.SwappableBeforeAdvice"/>

This is the advice which advise all setter methods on the bean

    <bean id="settersAdvisor"
        class="org.springframework.aop.support.RegexpMethodPointcutAdvisor">
        <property name="advice">
            <ref local="swapableBeforeAdvice" />
        </property>
        <property name="patterns">
            <list>
                <value>.*set.*</value>
            </list>
        </property>
    </bean>
  

Thanks to this post in spring forum which helped me do this.

http://forum.springsource.org/showthread.php?t=102784