@Before advice in Spring Boot - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ component_behavior

intermediate

What happens when a @Before advice is applied in Spring AOP?

Consider a Spring Boot application using AspectJ style @Before advice. What is the behavior of the @Before advice when the target method is called?

Spring Boot

@Aspect
@Component
public class LoggingAspect {
  @Before("execution(* com.example.service.*.*(..))")
  public void logBefore() {
    System.out.println("Method is about to execute");
  }
}

A The advice runs before the target method executes, printing the message each time the method is called.

B The advice runs after the target method executes, printing the message only if the method completes successfully.

C The advice runs only if the target method throws an exception.

D The advice runs concurrently with the target method, possibly causing race conditions.

💡 Hint

Think about when @Before advice is triggered in the method call lifecycle.

The @Before advice in Spring AOP runs before the target method executes. It allows you to run code right before the method starts, such as logging or validation.

📝 Syntax

intermediate

Identify the correct syntax for a @Before advice method in Spring AOP

Which of the following method signatures correctly defines a @Before advice in a Spring Boot Aspect class?

A

@Before
public void beforeMethod() {}

B

@Before("execution(* com.example..*(..))")
public void beforeMethod(String arg) {}

C

@Before("execution(* com.example..*(..))")
public String beforeMethod() { return "ok"; }

D

@Before("execution(* com.example..*(..))")
public void beforeMethod() {}

💡 Hint

Check the annotation usage and method signature requirements for @Before advice.

The @Before advice method must be void and take no arguments unless using JoinPoint or other special parameters. The annotation requires a pointcut expression.

🔧 Debug

advanced

Why does this @Before advice not execute?

Given the following Aspect code, why does the @Before advice never run when calling methods in com.example.service.UserService?

Spring Boot

package com.example.aspect;

import org.aspectj.lang.annotation.Aspect;
import org.aspectj.lang.annotation.Before;
import org.springframework.stereotype.Component;

@Aspect
@Component
public class LoggingAspect {

  @Before("execution(* com.example.service.UserService.*(..))")
  public void logBefore() {
    System.out.println("Before method call");
  }
}

// UserService is annotated with @Service and methods are public.

A The aspect class is missing @EnableAspectJAutoProxy annotation in the Spring configuration.

B The pointcut expression is incorrect; it should use 'within' instead of 'execution'.

C The advice method must return a value to execute.

D The UserService methods are private, so advice cannot be applied.

💡 Hint

Check if Spring AOP proxying is enabled in the configuration.

Spring AOP requires @EnableAspectJAutoProxy in a configuration class to enable proxy-based aspects. Without it, aspects are not applied.

❓ state_output

advanced

What is the output when @Before advice modifies a method argument?

Consider this Aspect and service method. What will be printed when calling process("hello")?

Spring Boot

package com.example.aspect;

import org.aspectj.lang.JoinPoint;
import org.aspectj.lang.annotation.Aspect;
import org.aspectj.lang.annotation.Before;
import org.springframework.stereotype.Component;

@Aspect
@Component
public class ModifyArgAspect {
  @Before("execution(* com.example.service.MessageService.process(String)) && args(msg)")
  public void beforeProcess(JoinPoint jp, String msg) {
    System.out.println("Before: " + msg);
    msg = msg.toUpperCase();
  }
}

package com.example.service;

public class MessageService {
  public void process(String message) {
    System.out.println("Processing: " + message);
  }
}

A

Before: hello
Processing: HELLO

B

Before: hello
Processing: hello

C

Before: HELLO
Processing: hello

D Compilation error due to argument modification in advice

💡 Hint

Think about whether changing the parameter inside advice affects the original method argument.

In Java, method arguments are passed by value. Modifying the parameter inside advice does not change the original argument passed to the target method.

🧠 Conceptual

expert

Which statement about @Before advice and exceptions is true?

In Spring AOP, what happens if a @Before advice throws an exception during execution?

A The exception is caught and logged, then the target method executes.

B The exception is ignored, and the target method executes normally.

C The target method is not executed, and the exception propagates to the caller.

D The target method executes first, then the exception is thrown.

💡 Hint

Consider the order of execution and exception handling in advice.

If a @Before advice throws an exception, it prevents the target method from running. The exception propagates up the call stack.