Accessing Spring Proxies - Reflection and Advised

Accessing Spring Proxies - Reflection and Advised

a reoccuring issue that i've struck when using Spring is trying to work with a proxied object in reflection.  it's not something that occurs all the time, and there's very smart people doing very smart things with this, but here's what i've found works… Advised

basically, when you retrieve an object that's been proxied by Spring, it can be cast to an Advised object that can then be used to retrieve the underlying object.  

if you execute the underlying object though, you don't get the advantage of whatever aspect you had added so beware of that.

in any event, here's the code to get a quick sample up and running.

here's our holder

	package org.incompletecode.proxy;
	public class ProxyHolder {
	private ProxiedClass proxiedClass;
	public void useProxiedClass() {
	proxiedClass.doSomething();
	}
	public void setProxiedClass(ProxiedClass proxiedClass) {
	this.proxiedClass = proxiedClass;
	}
	}

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here's the proxied class

	package org.incompletecode.proxy;
	public class ProxiedClass {
	public void doSomething() {
	System.out.println("hello world");
	}
	}

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here's our aspect

	package org.incompletecode.proxy.aspect;
	import org.aspectj.lang.ProceedingJoinPoint;
	public class ProxiedClassAspect {
	public Object around(ProceedingJoinPoint proceedingJoinPoint) throws Throwable {
	//add something to the visibility
	System.out.println("before executing...");
	Object result = proceedingJoinPoint.proceed();//let it continue
	System.out.println("... after executing");
	//carry on
	return result;
	}
	}

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and here's our context 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:aop="http://www.springframework.org/schema/aop"
	xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd
	http://www.springframework.org/schema/aop http://www.springframework.org/schema/aop/spring-aop-3.1.xsd">
	<aop:config>
	<aop:aspect ref="proxiedClassAspect">
	<aop:around method="around" pointcut-ref="aroundRef"/>
	<aop:pointcut expression="execution(* org.incompletecode.proxy.ProxiedClass.doSomething())" id="aroundRef"/>
	</aop:aspect>
	</aop:config>
	<bean id="proxyHolder"
	class="org.incompletecode.proxy.ProxyHolder">
	<property name="proxiedClass" ref="proxiedClass"/>
	</bean>
	<bean id="proxiedClass"
	class="org.incompletecode.proxy.ProxiedClass">
	</bean>
	<bean id="proxiedClassAspect"
	class="org.incompletecode.proxy.aspect.ProxiedClassAspect">
	</bean>
	</beans>

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now, finally, the test that shows what can be done

	package org.incompletecode.proxy;
	import java.lang.reflect.Field;
	import org.junit.Test;
	import org.junit.runner.RunWith;
	import org.springframework.aop.framework.Advised;
	import org.springframework.beans.factory.annotation.Autowired;
	import org.springframework.test.context.ContextConfiguration;
	import org.springframework.test.context.junit4.SpringJUnit4ClassRunner;
	@RunWith(SpringJUnit4ClassRunner.class)
	@ContextConfiguration({"classpath:/META-INF/spring/application-context.xml"})
	public class ProxyHolderTest {
	@Autowired
	private ProxyHolder holder;
	@Test
	public void test() throws Exception {
	//lets do a plain run first
	holder.useProxiedClass();
	//now lets use reflection to retrieve the object
	for (Field field : holder.getClass().getDeclaredFields()) {
	if (field.getType().equals(ProxiedClass.class)) {
	//got our field, lets get the object
	field.setAccessible(true);
	//show it first to see that it's proxied
	Object object = field.get(holder);
	System.out.println(object.getClass().getName());
	//now cast to get the underlying object
	ProxiedClass proxiedClass = (ProxiedClass)((Advised)object).getTargetSource().getTarget();
	System.out.println(proxiedClass.getClass().getName());
	//now execute directly
	proxiedClass.doSomething();
	}
	}
	}
	}

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