Core Terminology

• Target: Object being enhanced
• Joinpoint: Method eligible for interception
• Pointcut: Method actually intercepted
• Advice
• Weaving: Process of applying advice to target
• Proxy: Enhanced object created after weaving
• Aspect: Combination of pointcut and advice

Implementation Mechanisms

• JDK Dynamic Proxy (for interface implementations)
• Cglib Dynamic Proxy (to non-interface classes)

Pointcut Expression Syntax

Format: execution("modifier return_type package.class.method(parameters) throws_exception")

Advice Types

@Aspect
@Component
public class AspectHandler {

    @Pointcut("execution(* com.example.service.*.*(..))")
    public void serviceMethods() {}
    
    @Before("serviceMethods()")
    public void beforeExecution(JoinPoint joinPoint) {
        System.out.println("Pre-execution advice");
    }
    
    @AfterReturning(value = "serviceMethods()", returning = "result")
    public void afterSuccess(JoinPoint joinPoint, Object result) {
        System.out.println("Post-execution result: " + result);
    }
    
    @Around("serviceMethods()")
    public Object wrapExecution(ProceedingJoinPoint pjp) throws Throwable {
        System.out.println("Around advice - pre");
        Object output = pjp.proceed();
        System.out.println("Around advice - post");
        return output;
    }
    
    @AfterThrowing(value = "serviceMethods()", throwing = "ex")
    public void onFailure(Throwable ex) {
        System.out.println("Exception handler: " + ex.getMessage());
    }
    
    @After("serviceMethods()")
    public void finalizeOperation() {
        System.out.println("Finalization advice");
    }
}

Execution Order in Multiple Aspects

Use @Order(value) to define sequence where lower values have higher priority

Alternative Pointcut Expressions

• within: Class-level matching
• args: Paramter-based matching
• this/target: Proxy/target type matching
• @within: Annotation on class
• @annotation: Annotation on method
• @args: Annotation on method parameters

Interface Annotation Interception Solution

public class AnnotationPointcut extends StaticMethodMatcherPointcut {
    @Override
    public boolean matches(Method method, Class> targetClass) {
        return AnnotationUtils.findAnnotation(method, CustomAnnotation.class) != null;
    }
}

public class AnnotationInterceptor implements MethodInterceptor {
    @Override
    public Object invoke(MethodInvocation invocation) throws Throwable {
        long start = System.currentTimeMillis();
        try {
            return invocation.proceed();
        } finally {
            System.out.println("Execution time: " + (System.currentTimeMillis() - start));
        }
    }
}

public class AnnotationAdvisor extends AbstractBeanFactoryPointcutAdvisor {
    private Pointcut customPointcut;
    
    @Override
    public Pointcut getPointcut() {
        return customPointcut;
    }
}

@Configuration
public class AopConfig {
    @Bean
    public AnnotationAdvisor annotationAdvisor() {
        AnnotationAdvisor advisor = new AnnotationAdvisor();
        advisor.setCustomPointcut(new AnnotationPointcut());
        advisor.setAdvice(new AnnotationInterceptor());
        return advisor;
    }
}