AOP for logging in Spring Boot - Step-by-Step Execution

Concept Flow - AOP for logging

Start Application

↓

Method Call

↓

AOP Interceptor

↓

Log Before

↓

Log After

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Return Result

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End Method Execution

When a method is called, AOP intercepts it to log before and after execution, then proceeds with the method and returns the result.

Execution Sample

Spring Boot

@Aspect
@Component
public class LoggingAspect {
  @Before("execution(* com.example..*(..))")
  public void logBefore() { System.out.println("Method start"); }
  @After("execution(* com.example..*(..))")
  public void logAfter() { System.out.println("Method end"); }
}

This code logs messages before and after any method in com.example package runs.

Execution Table

Step	Action	Evaluation	Result
1	Application starts	Spring loads beans	LoggingAspect bean created
2	Call method com.example.Service.doWork()	Matches pointcut expression	AOP interceptor triggers
3	Execute @Before advice	Print 'Method start'	Message logged before method
4	Proceed with original method	Method executes normally	Method logic runs
5	Execute @After advice	Print 'Method end'	Message logged after method
6	Return method result	Method returns value	Caller receives result

💡 Method execution completes, AOP advices finished

Variable Tracker

Variable	Start	After Step 3	After Step 5	Final
logMessages	[]	["Method start"]	["Method start", "Method end"]	["Method start", "Method end"]
methodResult	null	null	null	someValue

Key Moments - 3 Insights

Why does the logBefore method run before the actual method?

Because the @Before advice is triggered by the pointcut before the method executes, as shown in execution_table step 3.

Does the original method run before or after the logging?

The original method runs after the @Before advice and before the @After advice, as shown in execution_table step 4.

What happens if the method throws an exception?

The @After advice still runs after method execution, but to log only on success or failure, use @AfterReturning or @AfterThrowing advices.

Visual Quiz - 3 Questions

Look at the execution table, what is logged at step 3?

A No log

B "Method start"

C "Method end"

D "Method running"

💡 Hint

Check the 'Action' and 'Result' columns at step 3 in the execution_table.

At which step does the original method execute?

A Step 4

B Step 3

C Step 2

D Step 5

💡 Hint

Look for 'Proceed with original method' in the 'Action' column.

If we remove the @After advice, what changes in the variable 'logMessages'?

A It will contain both "Method start" and "Method end"

B It will be empty

C It will only contain "Method start"

D It will contain only "Method end"

💡 Hint

Refer to variable_tracker row for 'logMessages' after Step 5.

Concept Snapshot

AOP for logging in Spring Boot:
- Use @Aspect and @Component to define aspect class
- Use @Before to log before method execution
- Use @After to log after method execution
- Pointcut expression defines which methods to intercept
- Logs help track method start and end without changing method code

Full Transcript

This visual execution shows how Spring Boot uses AOP for logging. When the application starts, the LoggingAspect bean is created. When a method in the com.example package is called, the AOP interceptor triggers. First, the @Before advice logs 'Method start'. Then the original method runs. After it finishes, the @After advice logs 'Method end'. Finally, the method returns its result. Variables track the logged messages and method result. Key moments clarify why logging happens before and after the method. The quiz tests understanding of the execution steps and variable changes.