Introduction to LangChain: Make AI Smarter and Easier to use

In this article, we introduce how to use AOP with the @AspectJ Annotation. If we want to use this Annotation. we should include below code in the XML schema-based configuration file.

<aop:aspectj-autoproxy/> 

And also you need to add these libraries to your project, aspectjrt.jar, aspectjweaver.jar, aspectj.jar and aopalliance.jar.

Declare Aspect

Using @Aspect annotation to the class which you want to appoint it as an Aspect.

@Aspect
public class MyLogging {
	// some codes in here
}

Declare Pointcut

Declaring pointcut in your aspect module with @Pointcut annotation.

@Aspect
public class MyLogging {
	
	@Pointcut("execution(* spring.test.aop.MyData.saveData(..))")
	private void saveDataPointcut() {
		
	}
}

In above codes, the pointcut is only work for saveData method of MyData class in the spring.test.aop package. To see the regular expression, go to here

Delcare Advice

We can declare more types of advice using specific annotation in the aspect module, like @Before, @After, @AfterReturning, @AfterThrowing, @Around. Let’s see the codes directly.

@Aspect
public class MyLogging {

	@Pointcut("execution(* spring.test.aop.MyData.saveData(..))")
	private void saveDataPointcut() {

	}

	@Before("saveDataPointcut()")
	public void beforeSaveData() {
		System.out.println("The Data is going to be saved");
	}

	@After("saveDataPointcut()")
	public void afterSaveData() {
		System.out.println("The Data has been saved");
	}

	@Before("execution(* spring.test.aop.MyData.getData())")
	public void beforeGetData() {
		System.out.println("Ready to get the data");
	}

	@After("execution(* spring.test.aop.*.getData())")
	public void afterGetData() {
		System.out.println("The data has been got");
	}

	@AfterReturning(pointcut = "execution(* spring.test.aop.MyData.getData())", returning = "returnValue")
	public void afterReturningAdvice(Object returnValue) {
		System.out.println(String.format("The return value is: %s ",
				returnValue.toString()));
	}

	@AfterThrowing(pointcut = "execution(* spring.test.aop.*.concatData(..))", throwing = "ex")
	public void throwingAdvice(NullPointerException ex) {
		System.out.println(String.format("Throw exception is: %s",
				ex.getMessage()));
	}

	@Around("saveDataPointcut()")
	public void aroundAdvice(ProceedingJoinPoint point) throws Throwable {
		System.out.println("Saving Data....");

		point.proceed();

		System.out.println("Saved Data!");
	}

}

You can specify the pointcut name or pointcut expression to advice. whatever you want. One important thing is you must let the advice know which pointcut works for.

Simple Instance

MyData.java

package spring.test.aop;

public class MyData {
	public String data;

	public void saveData(String data) {
		System.out.println("Saving the data: " + data);
		this.data = data;
	}

	public String getData() {
		System.out.println("Get the data: " + this.data);
		return this.data;
	}
	
	public void concatData(String data) {
		this.data.concat(data);
	}
}

MyLogging.java

package spring.test.aop;

import org.aspectj.lang.ProceedingJoinPoint;
import org.aspectj.lang.annotation.After;
import org.aspectj.lang.annotation.AfterReturning;
import org.aspectj.lang.annotation.AfterThrowing;
import org.aspectj.lang.annotation.Around;
import org.aspectj.lang.annotation.Aspect;
import org.aspectj.lang.annotation.Before;
import org.aspectj.lang.annotation.Pointcut;

@Aspect
public class MyLogging {

	@Pointcut("execution(* spring.test.aop.MyData.saveData(..))")
	private void saveDataPointcut() {

	}

	@Before("saveDataPointcut()")
	public void beforeSaveData() {
		System.out.println("The Data is going to be saved");
	}

	@After("saveDataPointcut()")
	public void afterSaveData() {
		System.out.println("The Data has been saved");
	}

	@Before("execution(* spring.test.aop.MyData.getData())")
	public void beforeGetData() {
		System.out.println("Ready to get the data");
	}

	@After("execution(* spring.test.aop.*.getData())")
	public void afterGetData() {
		System.out.println("The data has been got");
	}

	@AfterReturning(pointcut = "execution(* spring.test.aop.MyData.getData())", returning = "returnValue")
	public void afterReturningAdvice(Object returnValue) {
		System.out.println(String.format("The return value is: %s ",
				returnValue.toString()));
	}

	@AfterThrowing(pointcut = "execution(* spring.test.aop.*.concatData(..))", throwing = "ex")
	public void throwingAdvice(NullPointerException ex) {
		System.out.println(String.format("Throw exception is: %s",
				ex.getMessage()));
	}

	@Around("saveDataPointcut()")
	public void aroundAdvice(ProceedingJoinPoint point) throws Throwable {
		System.out.println("Saving Data....");

		point.proceed();

		System.out.println("Saved Data!");
	}

}

springConfig.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-3.0.xsd 
    http://www.springframework.org/schema/aop 
    http://www.springframework.org/schema/aop/spring-aop-3.0.xsd ">
    
    <aop:aspectj-autoproxy/>
	
	<bean id="myLogging" class="spring.test.aop.MyLogging" />
	
	<bean id="myData" class="spring.test.aop.MyData" />
</beans>

App.java

package spring.test.aop;

import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;

public class App {

	private static ApplicationContext context;

	public static void main(String[] args) {
		context = new ClassPathXmlApplicationContext("springConfig.xml");

		MyData myData = (MyData) context.getBean("myData");

		myData.saveData("35");
		
		System.out.println("-----------------");
		myData.getData();
		
		System.out.println("-----------------");
		myData.concatData(null);
	}

}

Okay, run above simple instance. the output is below:

Saving Data....
The Data is going to be saved
Saving the data: 35
Saved Data!
The Data has been saved
-----------------
Ready to get the data
Get the data: 35
The data has been got
The return value is: 35 
-----------------
Throw exception is: null
Exception in thread "main" java.lang.NullPointerException
...