Spring AOP Example – Advice

Spring AOP + AspectJ
Using AspectJ is more flexible and powerful, please refer to this tutorial – Using AspectJ annotation in Spring AOP.

Spring AOP (Aspect-oriented programming) framework is used to modularize cross-cutting concerns in aspects. Put it simple, it’s just an interceptor to intercept some processes, for example, when a method is execute, Spring AOP can hijack the executing method, and add extra functionality before or after the method execution.

In Spring AOP, 4 type of advices are supported :

  • Before advice – Run before the method execution
  • After returning advice – Run after the method returns a result
  • After throwing advice – Run after the method throws an exception
  • Around advice – Run around the method execution, combine all three advices above.

Following example show you how Spring AOP advice works.

Simple Spring example

Create a simple customer service class with few print methods for demonstration later.

package com.mkyong.customer.services;
 
public class CustomerService {
	private String name;
	private String url;
 
	public void setName(String name) {
		this.name = name;
	}
 
	public void setUrl(String url) {
		this.url = url;
	}
 
	public void printName() {
		System.out.println("Customer name : " + this.name);
	}
 
	public void printURL() {
		System.out.println("Customer website : " + this.url);
	}
 
	public void printThrowException() {
		throw new IllegalArgumentException();
	}
 
}

File : Spring-Customer.xml – A bean configuration file

<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-2.5.xsd">
 
	<bean id="customerService" class="com.mkyong.customer.services.CustomerService">
		<property name="name" value="Yong Mook Kim" />
		<property name="url" value="http://www.mkyong.com" />
	</bean>
 
</beans>

Run it

package com.mkyong.common;
 
import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;
 
import com.mkyong.customer.services.CustomerService;
 
public class App {
	public static void main(String[] args) {
		ApplicationContext appContext = new ClassPathXmlApplicationContext(
				new String[] { "Spring-Customer.xml" });
 
		CustomerService cust = (CustomerService) appContext.getBean("customerService");
 
		System.out.println("*************************");
		cust.printName();
		System.out.println("*************************");
		cust.printURL();
		System.out.println("*************************");
		try {
			cust.printThrowException();
		} catch (Exception e) {
 
		}
 
	}
}

Output

*************************
Customer name : Yong Mook Kim
*************************
Customer website : http://www.mkyong.com
*************************

A simple Spring project to DI a bean and output some Strings.

Spring AOP Advices

Now, attach Spring AOP advices to above customer service.

1. Before advice

It will execute before the method execution. Create a class which implements MethodBeforeAdvice interface.

package com.mkyong.aop;
 
import java.lang.reflect.Method;
import org.springframework.aop.MethodBeforeAdvice;
 
public class HijackBeforeMethod implements MethodBeforeAdvice
{
	@Override
	public void before(Method method, Object[] args, Object target)
		throws Throwable {
	        System.out.println("HijackBeforeMethod : Before method hijacked!");
	}
}

In bean configuration file (Spring-Customer.xml), create a bean for HijackBeforeMethod class , and a new proxy object named ‘customerServiceProxy‘.

  • ‘target’ – Define which bean you want to hijack.
  • ‘interceptorNames’ – Define which class (advice) you want to apply on this proxy /target object.
<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-2.5.xsd">
 
	<bean id="customerService" class="com.mkyong.customer.services.CustomerService">
		<property name="name" value="Yong Mook Kim" />
		<property name="url" value="http://www.mkyong.com" />
	</bean>
 
	<bean id="hijackBeforeMethodBean" class="com.mkyong.aop.HijackBeforeMethod" />
 
	<bean id="customerServiceProxy" 
                 class="org.springframework.aop.framework.ProxyFactoryBean">
 
		<property name="target" ref="customerService" />
 
		<property name="interceptorNames">
			<list>
				<value>hijackBeforeMethodBean</value>
			</list>
		</property>
	</bean>
</beans>
Note
To use Spring proxy, you need to add CGLIB2 library. Add below in Maven pom.xml file.

	<dependency>
		<groupId>cglib</groupId>
		<artifactId>cglib</artifactId>
		<version>2.2.2</version>
	</dependency>

Run it again, now you get the new customerServiceProxybean instead of the original customerService bean.

package com.mkyong.common;
 
import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;
import com.mkyong.customer.services.CustomerService;
 
public class App {
	public static void main(String[] args) {
		ApplicationContext appContext = new ClassPathXmlApplicationContext(
				new String[] { "Spring-Customer.xml" });
 
		CustomerService cust = 
                                (CustomerService) appContext.getBean("customerServiceProxy");
 
		System.out.println("*************************");
		cust.printName();
		System.out.println("*************************");
		cust.printURL();
		System.out.println("*************************");
		try {
			cust.printThrowException();
		} catch (Exception e) {
 
		}
 
	}
}

Output

*************************
HijackBeforeMethod : Before method hijacked!
Customer name : Yong Mook Kim
*************************
HijackBeforeMethod : Before method hijacked!
Customer website : http://www.mkyong.com
*************************
HijackBeforeMethod : Before method hijacked!

It will run the HijackBeforeMethod’s before() method, before every customerService’s methods are execute.

2. After returning advice

It will execute after the method is returned a result. Create a class which implements AfterReturningAdvice interface.

package com.mkyong.aop;
 
import java.lang.reflect.Method;
import org.springframework.aop.AfterReturningAdvice;
 
public class HijackAfterMethod implements AfterReturningAdvice
{
	@Override
	public void afterReturning(Object returnValue, Method method,
		Object[] args, Object target) throws Throwable {
	        System.out.println("HijackAfterMethod : After method hijacked!");
	}
}

Bean configuration file

<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-2.5.xsd">
 
	<bean id="customerService" class="com.mkyong.customer.services.CustomerService">
		<property name="name" value="Yong Mook Kim" />
		<property name="url" value="http://www.mkyong.com" />
	</bean>
 
	<bean id="hijackAfterMethodBean" class="com.mkyong.aop.HijackAfterMethod" />
 
	<bean id="customerServiceProxy" 
                class="org.springframework.aop.framework.ProxyFactoryBean">
 
		<property name="target" ref="customerService" />
 
		<property name="interceptorNames">
			<list>
				<value>hijackAfterMethodBean</value>
			</list>
		</property>
	</bean>
</beans>

Run it again, Output

*************************
Customer name : Yong Mook Kim
HijackAfterMethod : After method hijacked!
*************************
Customer website : http://www.mkyong.com
HijackAfterMethod : After method hijacked!
*************************

It will run the HijackAfterMethod’s afterReturning() method, after every customerService’s methods that are returned result.

3. After throwing advice

It will execute after the method throws an exception. Create a class which implements ThrowsAdvice interface, and create a afterThrowing method to hijack the IllegalArgumentException exception.

package com.mkyong.aop;
 
import org.springframework.aop.ThrowsAdvice;
 
public class HijackThrowException implements ThrowsAdvice {
	public void afterThrowing(IllegalArgumentException e) throws Throwable {
		System.out.println("HijackThrowException : Throw exception hijacked!");
	}
}

Bean configuration file

<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-2.5.xsd">
 
	<bean id="customerService" class="com.mkyong.customer.services.CustomerService">
		<property name="name" value="Yong Mook Kim" />
		<property name="url" value="http://www.mkyong.com" />
	</bean>
 
	<bean id="hijackThrowExceptionBean" class="com.mkyong.aop.HijackThrowException" />
 
	<bean id="customerServiceProxy" 
                 class="org.springframework.aop.framework.ProxyFactoryBean">
 
		<property name="target" ref="customerService" />
 
		<property name="interceptorNames">
			<list>
				<value>hijackThrowExceptionBean</value>
			</list>
		</property>
	</bean>
</beans>

Run it again, output

*************************
Customer name : Yong Mook Kim
*************************
Customer website : http://www.mkyong.com
*************************
HijackThrowException : Throw exception hijacked!

It will run the HijackThrowException’s afterThrowing() method, if customerService’s methods throw an exception.

4. Around advice

It combines all three advices above, and execute during method execution. Create a class which implements MethodInterceptor interface. You have to call the “methodInvocation.proceed();” to proceed on the original method execution, else the original method will not execute.

package com.mkyong.aop;
 
import java.util.Arrays;
 
import org.aopalliance.intercept.MethodInterceptor;
import org.aopalliance.intercept.MethodInvocation;
 
public class HijackAroundMethod implements MethodInterceptor {
	@Override
	public Object invoke(MethodInvocation methodInvocation) throws Throwable {
 
		System.out.println("Method name : "
				+ methodInvocation.getMethod().getName());
		System.out.println("Method arguments : "
				+ Arrays.toString(methodInvocation.getArguments()));
 
		// same with MethodBeforeAdvice
		System.out.println("HijackAroundMethod : Before method hijacked!");
 
		try {
			// proceed to original method call
			Object result = methodInvocation.proceed();
 
			// same with AfterReturningAdvice
			System.out.println("HijackAroundMethod : Before after hijacked!");
 
			return result;
 
		} catch (IllegalArgumentException e) {
			// same with ThrowsAdvice
			System.out.println("HijackAroundMethod : Throw exception hijacked!");
			throw e;
		}
	}
}

Bean configuration file

<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-2.5.xsd">
 
	<bean id="customerService" class="com.mkyong.customer.services.CustomerService">
		<property name="name" value="Yong Mook Kim" />
		<property name="url" value="http://www.mkyong.com" />
	</bean>
 
	<bean id="hijackAroundMethodBean" class="com.mkyong.aop.HijackAroundMethod" />
 
	<bean id="customerServiceProxy" 
                class="org.springframework.aop.framework.ProxyFactoryBean">
 
		<property name="target" ref="customerService" />
 
		<property name="interceptorNames">
			<list>
				<value>hijackAroundMethodBean</value>
			</list>
		</property>
	</bean>
</beans>

Run it again, output

*************************
Method name : printName
Method arguments : []
HijackAroundMethod : Before method hijacked!
Customer name : Yong Mook Kim
HijackAroundMethod : Before after hijacked!
*************************
Method name : printURL
Method arguments : []
HijackAroundMethod : Before method hijacked!
Customer website : http://www.mkyong.com
HijackAroundMethod : Before after hijacked!
*************************
Method name : printThrowException
Method arguments : []
HijackAroundMethod : Before method hijacked!
HijackAroundMethod : Throw exception hijacked!

It will run the HijackAroundMethod’s invoke()method, after every customerService’s method execution.

Conclusion

Most of the Spring developers are just implements the ‘Around advice ‘, since it can apply all the advice type, but a better practice should choose the most suitable advice type to satisfy the requirements.

Pointcut
In this example, all the methods in a customer service class are intercepted (advice) automatically. But for most cases, you may need to use Pointcut and Advisor to intercept a method via it’s method name.

Download Source Code

Download it – Spring-AOP-Advice-Examples.zip (8 KB)
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About the Author

mkyong
Founder of Mkyong.com and HostingCompass.com, love Java and open source stuff. Follow him on Twitter, or befriend him on Facebook or Google Plus. If you like my tutorials, consider make a donation to these charities.

Comments

  • praveenambati

    Why you not used namespace ?
    xmlns:aop=”http://www.springframework.org/schema/aop”

  • suresh kumar

    It’s a very good example for the AOP beginers

    Thanks and Regards,
    suresh kumar. somarouthu

  • http://[email protected] Sankha

    Example was nice but I still get that java.lang.ClassCastException: $Proxy0 error. Anybody got past this issue? how?

    Mr Mkyong, any suggestion please?

  • Sankha

    Example was nice, but I still get that java.lang.ClassCastException: $Proxy0 exception. Anybody get rid of this issue yet?
    Mr Mkyong, any suggestion please?

  • Mayur Mistry

    Nice and Simple example for Beginners

  • swapnil

    Thank you, this is really nice.
    Quite simple and straightforward explanation to understand for new person. Thank you again.

  • sijo

    Your tutorials are very useful . Great work ….

  • prakash

    Very nice article

  • Nathan

    Hello,

    I am a french student, beginner with Spring AOP Advice.

    This article is very simple and usefull. However, I would like to know how to do when (for example) CustomerService extends a class which has got an Interface ?

    I have the following error :
    “Exception in thread “main” java.lang.ClassCastException: $Proxy0 cannot be cast to com.mkyong.customer.services.CustomerService at com.mkyong.common.App.main(App.java:14)”

    Thank you for your help :)

    Have a nice day,

    Regards,

    Nathan

    • rohan

      I am getting the same error.How did you solve $proxy error0(classcastexception)

  • Meghna

    Nice post man… Even these http://www.compiletimeerror.com/search/label/Java-Spring%20framework might help… Have a look…

  • ali

    fast and Clean sample!
    thanks

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  • Ashok

    The most concise and simplest AOP examples to be found on the web. Thanks!

    One minor update: the ThrowsAdvice interface seems to have become no-op in Spring 2.5.5:

    // Compiled from ThrowsAdvice.java (version 1.4 : 48.0, no super bit)
    public abstract interface org.springframework.aop.ThrowsAdvice extends org.springframework.aop.AfterAdvice {
    }

  • mallesh

    Really helpfull for beginners

    thanks a lot

  • Sd590

    Really superb article for beginners like me. It is simply crystal clear and very meaningful. Thanks.

  • Ali

    Great work

    • anurag

      A nice explanation

  • Divya

    Really helpful for Beginners.

    Thanks a lot..

  • Vishwa

    Very nice article.

  • http://www.prism-it.com AK

    Its Great. Good article.
    But I tried the same but it is not taking beforemethodadvice… I added cglib jar file in build path.. But only thing is @override annotation in HijackBeforeAdvice is throwing me compilation error.. If I remove that, compilation error goes off but NOT RUNNING the HijackBeforeMethod’s before() method.

    Can anyone please help me in this regard…I get simple output not the advice output..

    Pleaazzzzz

    • nabeel

      which JVM version are you using? it should be 1.5 or above.

  • http://www.prism-it.com AK

    Its Great. Good article.
    But I tried the same but it is not taking beforemethodadvice… I added cglib jar file in build path.. But only thing is @override annotation in HijackBeforeAdvice is throwing me compilation error.. If I remove that, compilation error goes off but NOT RUNNING the HijackBeforeMethod’s before() method.

    Can anyone please help me in this regard…I get simple output not the advice output..

    Pleaazzzzz

    • Colin Hilbert

      I added aopalliance 1.0 jar to my build path and this error went away

      • Jaganathan

        Hi Colin,
        I am not getting any compilation error. But while running, I am getting the below exception. I am using the main program name as MainApp.java. Rest of the info are same as in this article. I have already added aopalliance jar to the buildpath. I am using eclipse.

        Exception in thread “main” org.springframework.beans.factory.BeanCreationException: Error creating bean with name ‘customerServiceProxy': FactoryBean threw exception on object creation; nested exception is java.lang.IncompatibleClassChangeError: org.springframework.asm.ClassVisitor
        at org.springframework.beans.factory.support.FactoryBeanRegistrySupport.doGetObjectFromFactoryBean(FactoryBeanRegistrySupport.java:149)
        at org.springframework.beans.factory.support.FactoryBeanRegistrySupport.getObjectFromFactoryBean(FactoryBeanRegistrySupport.java:102)
        at org.springframework.beans.factory.support.AbstractBeanFactory.getObjectForBeanInstance(AbstractBeanFactory.java:1454)
        at org.springframework.beans.factory.support.AbstractBeanFactory.doGetBean(AbstractBeanFactory.java:249)
        at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:194)
        at org.springframework.context.support.AbstractApplicationContext.getBean(AbstractApplicationContext.java:1117)
        at com.tutorialspoint.MainApp.main(MainApp.java:13)

        Thanks in Advance
        Jagan

        • TryCatch

          Where u able to find the solution for the above problem? I am also facing the same error

      • http://iSushantJain.blogspot.in Sushant Jain

        I also used that mentioned jar but still facing the same issue.
        Please tell me where to save “Spring-Customer.xml”
        I dont know how spring will find this Spring-Customer.xml in resource folder.
        Please help me.

  • Pintu Debnath

    Nicely described.. carry on…

  • arlahiru

    really helpful practical guide for beginners. thx lot!

  • Test

    Gr8 !! Super !!
    You Rock !!

  • Ravinder

    This example has set the foundation for me. It’s so simple and that’s all I needed to get started in AOP. I can now start to look more in depth at AOP.

    Fantastic work, keep it up.

    Regards

    Ravi

  • Karthick

    I’m using Spring 3.1.2 and all my controllers are annotation driven. My spring context xml will not have any beans defines in that. How to achieve AOP in that case. i.e., is it possible to achieve AOP through annotations(not AspectJ though). Is it possible? If so, please let me know.

    • petro

      Hi. Do you find the answer on your question?

  • Ramakant

    Hi,
    The example is nice. I am yet to read in depth about AOP but am wondering whether the AOP can be selective on methods. For ex, assuming a class has n methods in it and I want certain things to take place only when x methods are invoked (x<n) and for the remaining (n-x) methods, nothing should happen (no AOP behavior). Please let me know if this is something which is possible?

    Regards,
    Ramakant

    • khalil

      Yes , that is what mkYong mentionned in the end of the tutorial.refer to the next tutorial about Pointcut and Adviser

  • Rizvi

    Great work! I am very much impressed…

  • Skumar

    This is very Helpfull to a beginer and best practise..
    Thanks a lot ….

  • qazjvm

    Hi,

    My application context is:

    &lt;bean id=&quot;hijackAroundMethodBean&quot; class=&quot;org.poc.aspect.BusinessProfiler&quot; /&gt;
     
    	&lt;bean id=&quot;serviceProxy&quot; 
                    class=&quot;org.springframework.aop.framework.ProxyFactoryBean&quot;&gt;
     
    		&lt;property name=&quot;target&quot; ref=&quot;serviceImpl&quot; /&gt;
     
    		&lt;property name=&quot;interceptorNames&quot;&gt;
    			&lt;list&gt;
    				&lt;value&gt;hijackAroundMethodBean&lt;/value&gt;
    			&lt;/list&gt;
    		&lt;/property&gt;
    	&lt;/bean&gt;

    This refers to my service bean which is declared using @Qualifier annotation in my controller class. Hence there is no bean entry with this id in application context.
    No error is thrown but spring aop feature is not working.
    Please suggest a workaround.

    • qazjvm

      ***** Updating my post below ******

      In my web project, my service bean is declares as follows:

      @Controller
      public class MyController(){
       
      @Qualifier(&quot;serviceImpl&quot;)
      @Autowire
      Service service;
       
      /*-- remaining code here */

      }

  • Nicolas

    Clear and simple like all the other spring demo.
    Dude seriously, thank you for your work :). I’m sure it’ll help a lot of beginer

  • Shiju

    Hi
    I am getting a syntax error says
    The hierarchy of the type Hijack BeforeMethod is inconsistent
    at
    public class HijackBeforeMethod implements MethodBeforeAdvice{.

    what could be wrong??

  • Joe Jarin

    This article totally opened my mind :)