@Around advice for full control in Spring Boot

Introduction

@Around advice lets you wrap extra code before and after a method runs. It gives you full control to change inputs, outputs, or handle errors.

You want to log method start and end times with details.

You need to measure how long a method takes to run.

You want to modify the method's input parameters or output result.

You want to handle exceptions in a custom way around a method.

You want to add security checks before a method runs.

Syntax

Spring Boot

@Around("pointcutExpression")
public Object methodName(ProceedingJoinPoint joinPoint) throws Throwable {
    // code before method
    Object result = joinPoint.proceed();
    // code after method
    return result;
}

The method must return Object and throw Throwable.

Use joinPoint.proceed() to run the original method.

Examples

This example logs how long any method in com.example.service package takes to run.

Spring Boot

@Around("execution(* com.example.service.*.*(..))")
public Object logExecutionTime(ProceedingJoinPoint joinPoint) throws Throwable {
    long start = System.currentTimeMillis();
    Object proceed = joinPoint.proceed();
    long duration = System.currentTimeMillis() - start;
    System.out.println(joinPoint.getSignature() + " took " + duration + " ms");
    return proceed;
}

This example changes the first argument to uppercase before calling the original method.

Spring Boot

@Around("execution(* com.example.service.UserService.getUser(..))")
public Object modifyInput(ProceedingJoinPoint joinPoint) throws Throwable {
    Object[] args = joinPoint.getArgs();
    if(args.length > 0 && args[0] instanceof String) {
        args[0] = ((String) args[0]).toUpperCase();
    }
    return joinPoint.proceed(args);
}

Sample Program

This Spring Boot example uses @Around advice to measure how long any method in the service package takes to run. When the greet method runs, the aspect prints the execution time. The main app calls greet and prints the greeting.

Spring Boot

package com.example.demo.aspect;

import org.aspectj.lang.ProceedingJoinPoint;
import org.aspectj.lang.annotation.Around;
import org.aspectj.lang.annotation.Aspect;
import org.springframework.stereotype.Component;

@Aspect
@Component
public class TimingAspect {

    @Around("execution(* com.example.demo.service.*.*(..))")
    public Object measureTime(ProceedingJoinPoint joinPoint) throws Throwable {
        long start = System.currentTimeMillis();
        Object result = joinPoint.proceed();
        long end = System.currentTimeMillis();
        System.out.println(joinPoint.getSignature() + " executed in " + (end - start) + "ms");
        return result;
    }
}

// Service class
package com.example.demo.service;

import org.springframework.stereotype.Service;

@Service
public class GreetingService {
    public String greet(String name) {
        return "Hello, " + name + "!";
    }
}

// Main application to test
package com.example.demo;

import org.springframework.boot.CommandLineRunner;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import com.example.demo.service.GreetingService;

@SpringBootApplication
public class DemoApplication implements CommandLineRunner {

    private final GreetingService greetingService;

    public DemoApplication(GreetingService greetingService) {
        this.greetingService = greetingService;
    }

    public static void main(String[] args) {
        SpringApplication.run(DemoApplication.class, args);
    }

    @Override
    public void run(String... args) throws Exception {
        String message = greetingService.greet("Alice");
        System.out.println(message);
    }
}

Important Notes

Always call joinPoint.proceed() to continue the original method execution.

You can modify arguments by passing a new array to proceed(args).

Use @Around advice carefully as it can change method behavior and affect performance.

Summary

@Around advice wraps a method to run code before and after it.

It gives full control to modify inputs, outputs, or handle exceptions.

Remember to call joinPoint.proceed() to run the original method.

Practice

1. What is the main purpose of using @Around advice in Spring AOP?

easy

A. To run code before and after a method, controlling its execution fully

B. To only run code after a method finishes

C. To replace the method with a new implementation without calling the original

D. To log method parameters without affecting execution

Solution

1. Step 1: Understand the role of @Around advice

   @Around advice wraps a method, allowing code to run before and after the method execution.

2. Step 2: Compare options with this behavior

   Only To run code before and after a method, controlling its execution fully describes full control before and after the method, matching @Around's purpose.

3. Final Answer:

   To run code before and after a method, controlling its execution fully -> Option A

4. Quick Check:

   @Around advice = full control before and after method [OK]

Hint: Remember @Around wraps method execution fully [OK]

Common Mistakes:

• Thinking @Around only runs after method
• Confusing @Around with @After or @Before
• Forgetting @Around can modify inputs and outputs

2. Which of the following is the correct way to proceed with the original method inside an @Around advice method?

easy

A. return joinPoint.proceed();

B. joinPoint.execute();

C. proceed(joinPoint);

D. joinPoint.run();

Solution

1. Step 1: Recall the method to call original execution

   In @Around advice, the original method is executed by calling joinPoint.proceed().

2. Step 2: Match the correct syntax

   Only return joinPoint.proceed(); uses the correct method name and syntax to proceed.

3. Final Answer:

   return joinPoint.proceed(); -> Option A

4. Quick Check:

   Call original method with joinPoint.proceed() [OK]

Hint: Use joinPoint.proceed() to run original method [OK]

Common Mistakes:

• Using incorrect method names like execute() or run()
• Forgetting to return the result of proceed()
• Calling proceed() without parentheses

3. Given the following @Around advice code, what will be printed when someMethod() returns "Hello"?

@Around("execution(* someMethod())")
public Object aroundAdvice(ProceedingJoinPoint joinPoint) throws Throwable {
    System.out.println("Before");
    Object result = joinPoint.proceed();
    System.out.println("After");
    return result + " World";
}

medium

A. Before
Hello
After
World

B. Hello
Before
After
World

C. Before
After
Hello

D. Before
After
Hello World

Solution

1. Step 1: Trace the advice execution order

   The advice prints "Before", then calls the original method which returns "Hello", then prints "After".

2. Step 2: Understand the returned value

   The advice returns the original result plus " World", so the final returned string is "Hello World".

3. Final Answer:

   Before After Hello World -> Option D

4. Quick Check:

   Prints before and after, returns modified result [OK]

Hint: Remember @Around runs code before and after proceed() [OK]

Common Mistakes:

• Assuming original method output is unchanged
• Mixing print order with return value
• Forgetting to add " World" to result

4. Identify the error in this @Around advice method:

@Around("execution(* someMethod())")
public Object aroundAdvice(ProceedingJoinPoint joinPoint) {
    System.out.println("Start");
    Object result = joinPoint.proceed();
    System.out.println("End");
    return result;
}

medium

A. Incorrect annotation syntax

B. Missing throws Throwable declaration in method signature

C. Should call joinPoint.execute() instead of proceed()

D. Cannot return Object type from advice

Solution

1. Step 1: Check method signature requirements

   joinPoint.proceed() throws Throwable, so the advice method must declare throws Throwable or handle it.

2. Step 2: Identify missing throws declaration

   The method lacks "throws Throwable", causing a compile error.

3. Final Answer:

   Missing throws Throwable declaration in method signature -> Option B

4. Quick Check:

   proceed() throws Throwable, must declare it [OK]

Hint: Add throws Throwable when calling joinPoint.proceed() [OK]

Common Mistakes:

• Ignoring checked exceptions from proceed()
• Using wrong method name instead of proceed()
• Not matching annotation syntax

5. You want to create an @Around advice that modifies the input argument of a method before execution and changes the returned result after execution. Which approach correctly achieves this?

hard

A. Modify the method parameters directly without using proceed, then return null

B. Call joinPoint.proceed() without arguments, then ignore the result and return a new value

C. Modify the argument array via joinPoint.getArgs(), then call joinPoint.proceed(modifiedArgs), and finally modify the returned result before returning

D. Use joinPoint.proceed() and modify the result, but cannot change input arguments

Solution

1. Step 1: Understand argument modification in @Around advice

   You can get and modify method arguments using joinPoint.getArgs() and pass them to proceed() to change inputs.

2. Step 2: Modify the returned result after proceed()

   After calling proceed with modified arguments, you can change the returned value before returning it.

3. Final Answer:

   Modify the argument array via joinPoint.getArgs(), then call joinPoint.proceed(modifiedArgs), and finally modify the returned result before returning -> Option C

4. Quick Check:

   Change inputs with proceed(args), then modify output [OK]

Hint: Use proceed(modifiedArgs) to change inputs, then modify output [OK]

Common Mistakes:

• Calling proceed() without modified arguments when inputs need change
• Trying to change parameters directly without proceed()
• Ignoring returned result modification