@Before advice in Spring Boot - Step-by-Step Execution

Concept Flow - @Before advice

Method call starts

↓

@Before advice runs

↓

Original method executes

↓

Method call ends

When a method is called, the @Before advice runs first, then the original method runs, then the call ends.

Execution Sample

Spring Boot

import org.aspectj.lang.annotation.Aspect;
import org.aspectj.lang.annotation.Before;

@Aspect
public class MyAspect {
  @Before("execution(* MyService.doWork(..))")
  public void beforeAdvice() {
    System.out.println("Before advice runs");
  }
}

This code runs the beforeAdvice method before MyService.doWork() executes.

Execution Table

Step	Action	Output	Next Step
1	Call MyService.doWork()	No output yet	Run @Before advice
2	Run @Before advice	Prints: Before advice runs	Run original method
3	Run original method doWork()	Original method output (if any)	Method call ends
4	Method call ends	No further action	Exit

💡 Method call completes after original method runs

Variable Tracker

Variable	Start	After Step 2	After Step 3	Final
methodCall	not started	beforeAdvice executed	original method executed	completed

Key Moments - 2 Insights

Does the original method run before or after the @Before advice?

The @Before advice runs first, then the original method runs, as shown in execution_table step 2 and 3.

Can @Before advice change the return value of the original method?

No, @Before advice runs before the method but cannot change its return value; it only runs code before the method executes.

Visual Quiz - 3 Questions

Look at the execution table, what happens at step 2?

A The original method runs

B The @Before advice runs

C The method call ends

D No action happens

💡 Hint

Check the 'Action' column for step 2 in the execution_table

At which step does the original method execute?

A Step 3

B Step 2

C Step 1

D Step 4

💡 Hint

Look at the 'Action' column in execution_table for when the original method runs

If the @Before advice prints a message, when will it appear relative to the original method's output?

A After the original method's output

B At the same time as the original method's output

C Before the original method's output

D It will not appear

💡 Hint

Refer to the order of outputs in execution_table steps 2 and 3

Concept Snapshot

@Before advice runs before the target method.
It cannot change the method's return value.
Use @Before("pointcut") to specify where it applies.
It is useful for logging or setup before method runs.
Execution order: @Before advice -> original method -> end.

Full Transcript

When a method matched by the pointcut is called, the @Before advice runs first. This means any code inside the @Before method executes before the original method starts. For example, if you have a method doWork() and a @Before advice on it, the advice prints a message before doWork() runs. The method call then continues to the original method. The @Before advice cannot change the return value or stop the method; it only runs code before the method executes. This is useful for logging or preparing data before the main method runs.