@Before advice in Spring Boot - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is the purpose of the @Before advice in Spring AOP?

The @Before advice runs a method before the target method executes. It is used to perform actions like logging, security checks, or setting up resources before the main method runs.

beginner

How do you declare a @Before advice in Spring Boot?

You create a method annotated with @Before and provide a pointcut expression that matches the methods where you want the advice to run.

@Before("execution(* com.example.service.*.*(..))")
public void beforeAdvice() {
  // code to run before target method
}

intermediate

What is a pointcut expression in the context of @Before advice?

A pointcut expression defines which methods the advice should apply to. It uses patterns to match method names, packages, or classes.

intermediate

Can @Before advice modify the return value of the target method?

No, @Before advice runs before the method and cannot change the return value. To modify return values, use @Around advice.

beginner

Give a real-life example where @Before advice is useful.

Before a bank transaction method runs, @Before advice can check if the user is authenticated and log the transaction attempt.

What does @Before advice do in Spring AOP?

A Modifies the return value of the target method

B Runs code after the target method executes

C Runs code before the target method executes

D Handles exceptions thrown by the target method

@Before advice runs before the target method starts, allowing pre-processing.

Which annotation is used to declare a method as a @Before advice?

A @Before

B @After

C @Around

D @Pointcut

@Before marks a method to run before matched methods.

Can @Before advice stop the execution of the target method?

A Yes, by throwing an exception

B No, it always lets the method run

C Yes, by returning false

D No, it runs after the method

@Before advice can throw exceptions to prevent the target method from running.

What is a pointcut expression used for in @Before advice?

A To define when the advice runs

B To define which methods the advice applies to

C To modify method arguments

D To log method return values

Pointcut expressions select the methods where advice applies.

Which advice type allows modifying the return value of a method?

A @Before

B @AfterThrowing

C @After

D @Around

@Around advice can control method execution and modify return values.

Explain how @Before advice works in Spring Boot and give an example use case.

Think about what you want to do before a method runs.

Describe the difference between @Before advice and @Around advice.

Consider when each advice runs and what it can do.

Practice

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

easy

A. To replace the matched method entirely

B. To run code right before the matched method executes

C. To run code after the matched method completes

D. To handle exceptions thrown by the matched method

Solution

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

   @Before advice is designed to execute code just before the target method runs.

2. Step 2: Compare with other advice types

   @After runs after method completion, @Around can replace, and @AfterThrowing handles exceptions.

3. Final Answer:

   To run code right before the matched method executes -> Option B

4. Quick Check:

   @Before advice = runs before method [OK]

Hint: Remember: @Before means before method starts [OK]

Common Mistakes:

• Confusing @Before with @After or @Around advice
• Thinking @Before replaces the method
• Assuming @Before handles exceptions

2. Which of the following is the correct syntax to define a @Before advice method in Spring AOP?

easy

A. @Before("execution(* com.example.service.*.*(..))") public void logBefore() {}

B. @Before public void logBefore() { execution(* com.example.service.*.*(..)); }

C. @Before public void logBefore() execution(* com.example.service.*.*(..)) {}

D. @Before("logBefore()") public void execution(* com.example.service.*.*(..)) {}

Solution

1. Step 1: Identify correct @Before annotation usage

   The @Before annotation requires a pointcut expression as a string parameter inside parentheses and quotes.

2. Step 2: Check method signature and placement

   The method should be public void with no parameters or with JoinPoint if needed, and the pointcut is inside @Before("...").

3. Final Answer:

   @Before("execution(* com.example.service.*.*(..))") public void logBefore() {} -> Option A

4. Quick Check:

   @Before("pointcut") public void method() {} [OK]

Hint: Look for @Before with pointcut string in parentheses [OK]

Common Mistakes:

• Placing pointcut expression outside quotes
• Missing parentheses after @Before
• Incorrect method signature or missing public

3. Given the following code snippet, what will be printed when service.process() is called?

@Aspect
@Component
public class LoggingAspect {
  @Before("execution(* com.example.service.Service.process(..))")
  public void beforeProcess() {
    System.out.println("Before process");
  }
}

@Service
public class Service {
  public void process() {
    System.out.println("Processing");
  }
}

medium

A. Before process\nProcessing

B. Processing\nBefore process

C. Before process

D. Processing

Solution

1. Step 1: Understand @Before advice execution timing

   @Before advice runs before the matched method, so "Before process" prints first.

2. Step 2: Analyze method call output

   Then the actual method prints "Processing" after the advice.

3. Final Answer:

   Before process\nProcessing -> Option A

4. Quick Check:

   @Before prints first, then method output [OK]

Hint: @Before prints before method output [OK]

Common Mistakes:

• Assuming method prints before advice
• Thinking advice replaces method output
• Ignoring advice execution order

4. Identify the error in this @Before advice definition:

@Before("execution(* com.example..*(..))")
public void beforeMethod() {
  System.out.println("Before method");
}

medium

A. Advice method cannot have a body

B. Pointcut expression syntax is invalid

C. Method must return a value

D. Missing @Aspect annotation on the class

Solution

1. Step 1: Check class-level annotations

   For @Before advice to work, the class must be annotated with @Aspect to mark it as an aspect.

2. Step 2: Validate pointcut and method

   The pointcut expression is valid, and advice methods can have bodies and return void.

3. Final Answer:

   Missing @Aspect annotation on the class -> Option D

4. Quick Check:

   @Aspect missing = advice won't run [OK]

Hint: Always add @Aspect on the class with advice [OK]

Common Mistakes:

• Forgetting @Aspect on the aspect class
• Assuming advice methods must return values
• Misreading pointcut syntax errors

5. You want to log a message before any method in com.example.repository package is called, but only for methods starting with save. Which @Before pointcut expression correctly matches this?

hard

A. @Before("execution(* com.example.repository.save*(..))")

B. @Before("execution(* com.example.repository.*save*(..))")

C. @Before("execution(* com.example.repository..save*(..))")

D. @Before("execution(* com.example.repository.*.save*(..))")

Solution

1. Step 1: Understand pointcut syntax for package, class, and method

   To match methods starting with 'save' in any class of the com.example.repository package, use execution(* com.example.repository.*.save*(..)). However, if you want to include subpackages as well, use '..' instead of a single '*'.

2. Step 2: Analyze each option

   A matches only methods named save* in the package directly (no class wildcard), B is invalid syntax, C matches methods in any class in the package but not subpackages, D matches methods starting with save in the package and all subpackages.

3. Final Answer:

   @Before("execution(* com.example.repository..save*(..))") -> Option C

4. Quick Check:

   package..save*(..) = matches package and subpackages [OK]

Hint: Use package..save* to include subpackages and methods starting with save [OK]

Common Mistakes:

• Using incorrect wildcards or dots in method name
• Matching subpackages unintentionally
• Misplacing wildcards in pointcut expression