AOP for performance monitoring in Spring Boot - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to define an aspect class for performance monitoring.

Spring Boot

import org.aspectj.lang.annotation.[1];

@Aspect
public class PerformanceAspect {

}

Drag options to blanks, or click blank then click option'

AAspect

BComponent

CService

DRepository

Attempts:

3 left

💡 Hint

Common Mistakes

Using @Component instead of @Aspect

Forgetting to import the annotation

Confusing @Service with @Aspect

The @Aspect annotation marks the class as an aspect for AOP.

2fill in blank

medium

Complete the code to define a pointcut expression that matches all methods in the service package.

Spring Boot

@Pointcut("execution(* com.example.service..*[1]*(..))")
public void serviceMethods() {}

Drag options to blanks, or click blank then click option'

A+

B.

C*

D#

Attempts:

3 left

💡 Hint

Common Mistakes

Using '.' instead of '*' for method names

Using '+' which is for class inheritance

Using '#' which is not valid here

The * wildcard matches any method name in the specified package.

3fill in blank

hard

Fix the error in the advice method to correctly measure execution time.

Spring Boot

@Around("serviceMethods()")
public Object measureTime(ProceedingJoinPoint joinPoint) throws Throwable {
    long start = System.currentTimeMillis();
    Object result = joinPoint.[1]();
    long end = System.currentTimeMillis();
    System.out.println("Execution time: " + (end - start) + " ms");
    return result;
}

Drag options to blanks, or click blank then click option'

Aexecute

Bproceed

Crun

Dcall

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'execute' which does not exist

Using 'run' which is unrelated

Using 'call' which is invalid here

The proceed() method executes the target method and returns its result.

4fill in blank

hard

Fill both blanks to log the method name and execution time inside the advice.

Spring Boot

String methodName = joinPoint.getSignature().[1]();
System.out.println("Method " + methodName + " took " + [2] + " ms");

Drag options to blanks, or click blank then click option'

AgetName

Bend - start

CgetClassName

Dstart - end

Attempts:

3 left

💡 Hint

Common Mistakes

Using getClassName instead of getName

Subtracting times in wrong order

Printing variables before they are defined

getName() gets the method name. The difference end - start gives execution time.

5fill in blank

hard

Fill all three blanks to create a complete around advice that measures and logs execution time for service methods.

Spring Boot

@Around("[1]")
public Object logExecutionTime(ProceedingJoinPoint joinPoint) throws Throwable {
    long [2] = System.currentTimeMillis();
    Object result = joinPoint.proceed();
    long [3] = System.currentTimeMillis();
    System.out.println("Execution time: " + (end - start) + " ms");
    return result;
}

Drag options to blanks, or click blank then click option'

AserviceMethods()

Bstart

Cend

Dexecution(* com.example.repository..*(..))

Attempts:

3 left

💡 Hint

Common Mistakes

Using wrong pointcut expression

Mixing up start and end variable names

Forgetting to call proceed()

The pointcut serviceMethods() targets service methods. Variables start and end store timestamps before and after method execution.

Practice

1. What is the main purpose of using AOP for performance monitoring in Spring Boot?

easy

A. To measure method execution time without changing the method code

B. To change the business logic of methods

C. To add new REST endpoints automatically

D. To replace database queries with cached results

Solution

1. Step 1: Understand AOP's role in performance monitoring

   AOP allows adding extra code around methods without modifying their original code.

2. Step 2: Identify the purpose of timing code

   Timing code measures how long methods take to run, helping find slow parts.

3. Final Answer:

   To measure method execution time without changing the method code -> Option A

4. Quick Check:

   AOP measures time without code changes [OK]

Hint: AOP adds timing code outside main methods [OK]

Common Mistakes:

• Thinking AOP changes method logic
• Confusing AOP with adding endpoints
• Assuming AOP caches database queries

2. Which annotation is used in Spring AOP to wrap method execution for timing?

easy

A. @Before

B. @After

C. @Around

D. @Pointcut

Solution

1. Step 1: Recall Spring AOP advice types

   @Before runs before method, @After runs after, @Around wraps method execution.

2. Step 2: Identify which advice can measure execution time

   @Around can run code before and after method, so it can measure duration.

3. Final Answer:

   @Around -> Option C

4. Quick Check:

   @Around wraps method for timing [OK]

Hint: Use @Around to wrap and time methods [OK]

Common Mistakes:

• Using @Before or @After which can't measure duration
• Confusing @Pointcut with advice annotation
• Assuming @After runs before method

3. Given this AOP method, what will be printed if the target method takes 150ms to execute?

@Around("execution(* com.example.service.*.*(..))")
public Object measureTime(ProceedingJoinPoint pjp) throws Throwable {
  long start = System.currentTimeMillis();
  Object result = pjp.proceed();
  long end = System.currentTimeMillis();
  System.out.println("Execution time: " + (end - start) + " ms");
  return result;
}

medium

A. Execution time: 0 ms

B. No output printed

C. Execution time: 300 ms

D. Execution time: 150 ms

Solution

1. Step 1: Understand timing calculation

   The code records start time, runs the method, then records end time and prints the difference.

2. Step 2: Match timing with method duration

   If method takes 150ms, printed time is 150 ms.

3. Final Answer:

   Execution time: 150 ms -> Option D

4. Quick Check:

   Printed time matches method duration [OK]

Hint: Printed time equals method run duration [OK]

Common Mistakes:

• Assuming time is zero or double counted
• Thinking no output prints
• Confusing start and end time order

4. What is wrong with this AOP advice for measuring execution time?

@Around("execution(* com.example..*(..))")
public void measure(ProceedingJoinPoint pjp) throws Throwable {
  long start = System.currentTimeMillis();
  pjp.proceed();
  long end = System.currentTimeMillis();
  System.out.println("Time: " + (end - start));
}

medium

A. The pointcut expression is invalid

B. The method should return Object, not void

C. System.currentTimeMillis() cannot be used for timing

D. ProceedingJoinPoint cannot be used in @Around advice

Solution

1. Step 1: Check method signature for @Around advice

   @Around advice must return the result of pjp.proceed() to maintain method behavior.

2. Step 2: Identify missing return statement

   Method returns void but should return Object from pjp.proceed().

3. Final Answer:

   The method should return Object, not void -> Option B

4. Quick Check:

   @Around advice must return method result [OK]

Hint: @Around methods must return Object from proceed() [OK]

Common Mistakes:

• Forgetting to return pjp.proceed() result
• Thinking pointcut syntax is wrong
• Believing System.currentTimeMillis() is invalid

5. You want to monitor execution time of all service methods but exclude methods annotated with @SkipTiming. Which AOP pointcut expression correctly achieves this?

hard

A. execution(* com.example.service..*(..)) && !@annotation(com.example.SkipTiming)

B. execution(* com.example.service..*(..)) || @annotation(com.example.SkipTiming)

C. execution(* com.example.service..*(..)) && @annotation(com.example.SkipTiming)

D. !execution(* com.example.service..*(..)) && !@annotation(com.example.SkipTiming)

Solution

1. Step 1: Understand pointcut logic for inclusion and exclusion

   We want all service methods except those with @SkipTiming annotation.

2. Step 2: Use && with negation to exclude annotated methods

   Use 'execution(...) && !@annotation(...)' to include methods but exclude those annotated.

3. Final Answer:

   execution(* com.example.service..*(..)) && !@annotation(com.example.SkipTiming) -> Option A

4. Quick Check:

   Exclude annotated methods with !@annotation [OK]

Hint: Use && !@annotation to exclude methods [OK]

Common Mistakes:

• Using || which includes annotated methods
• Using && @annotation which includes only annotated
• Negating execution pointcut incorrectly