Pointcut expressions in Spring Boot - Practice Problems & Coding Challenges

Challenge - 5 Problems

🧠 Conceptual

intermediate

Understanding basic pointcut expression syntax

Which of the following pointcut expressions matches all methods in any class within the package com.example.service?

A within(com.example.service.*)

B execution(* com.example.service..*.*(..))

C execution(* com.example.service.*.*(..))

D within(com.example.service..*)

💡 Hint

Remember that execution matches method executions and within matches types. The single dot . matches one package level, double dot .. matches any subpackage levels.

The expression execution(* com.example.service.*.*(..)) matches any method in any class directly inside the com.example.service package. The single dot . means exactly one package level. The within expressions match types. The double dot .. matches subpackages, so execution(* com.example.service..*.*(..)) matches subpackages too, which is broader than asked.

❓ component_behavior

intermediate

Effect of pointcut on method interception

Given the pointcut expression execution(public * *(..)), which methods will be intercepted?

A All public methods regardless of class or package

B Only public methods in the current package

C All methods with any visibility in any class

D Only methods named 'public' in any class

💡 Hint

Look at the modifiers and wildcards in the expression carefully.

The expression execution(public * *(..)) matches any method with public visibility, any return type, any method name, and any number of parameters in any class or package.

📝 Syntax

advanced

Identify the syntax error in pointcut expression

Which option contains a syntax error in the pointcut expression?

A execution(* com.example.service.*.*(String, ..))

B execution(* com.example.service.*.*(String,))

C execution(* com.example.service.*.*(..))

D execution(* com.example..service.*.*(..))

💡 Hint

Check the parameter pattern syntax carefully, especially commas and ellipsis.

Option B has a trailing comma after String in the parameter list (String,), which is invalid syntax in pointcut expressions. The ellipsis .. is used to indicate zero or more parameters and must be used correctly without trailing commas.

🔧 Debug

advanced

Why does this pointcut not match any method?

Consider this pointcut expression: execution(* com.example..*Service+.save*(..)). It does not match any methods in your project. What is the most likely reason?

A The pointcut expects classes ending with 'Service' or subclasses, but your classes do not extend any superclass

B The '+' symbol is used incorrectly; it should be '*' to match subclasses

C The package pattern <code>com.example..</code> is invalid and causes no matches

D The method name pattern <code>save*</code> does not match because methods are named exactly 'save'

💡 Hint

Recall what the '+' symbol means in pointcut expressions.

The '+' symbol means matching the specified class and all its subclasses. If your classes do not extend any superclass named '*Service', then no classes match the pattern *Service+. This causes the pointcut to match no methods.

❓ lifecycle

expert

Order of pointcut evaluation in Spring AOP

In Spring AOP, when multiple pointcuts apply to the same method, in what order are they evaluated?

A Pointcuts are evaluated randomly at runtime

B Pointcuts are evaluated based on their declaration order in the XML configuration

C Pointcuts are evaluated in the order they are declared in the aspect class

D Pointcuts are evaluated based on the order of aspect precedence and then method signature specificity

💡 Hint

Think about how Spring resolves multiple aspects and pointcuts.

Spring evaluates pointcuts based on aspect precedence (which can be controlled by @Order or Ordered interface) and then by method signature specificity. This ensures predictable and consistent advice execution order.

Practice

1. What does a pointcut expression in Spring Boot primarily do?

easy

A. Create new methods dynamically at runtime

B. Define the database connection settings

C. Select methods where extra code (advice) should run

D. Replace existing methods with new implementations

Solution

1. Step 1: Understand the purpose of pointcut expressions

   Pointcut expressions specify where additional code, called advice, should be applied in existing methods without changing those methods.

2. Step 2: Differentiate from other concepts

   They do not create or replace methods, nor configure databases. Their role is to select join points (methods) for advice.

3. Final Answer:

   Select methods where extra code (advice) should run -> Option C

4. Quick Check:

   Pointcut expression = Select methods for advice [OK]

Hint: Pointcuts pick methods to add code without changing them [OK]

Common Mistakes:

• Confusing pointcuts with method creation
• Thinking pointcuts configure databases
• Believing pointcuts replace method code

2. Which of the following is the correct syntax to match all methods in package com.example.service using a pointcut expression?

easy

A. execution(* com.example.service..*(..))

B. execution(com.example.service.*.*(..))

C. execution(* com.example.service.*(..))

D. execution(* com.example.service.*.*(..))

Solution

1. Step 1: Understand the execution syntax

   The syntax execution(* com.example.service.*.*(..)) matches any return type, any class in the package com.example.service, and any method with any parameters.

2. Step 2: Analyze other options

   execution(com.example.service.*.*(..)) misses the wildcard for return type. execution(* com.example.service..*(..)) uses double dot .. which matches subpackages, not just the package. execution(* com.example.service.*(..)) misses the class wildcard.

3. Final Answer:

   execution(* com.example.service.*.*(..)) -> Option D

4. Quick Check:

   Use * for any class and method in package [OK]

Hint: Use * for any class and method in a package [OK]

Common Mistakes:

• Omitting the return type wildcard *
• Using .. instead of * for classes
• Missing method wildcard *

3. Given the pointcut expression execution(public * com.example.repo.*Repository.find*(..)), which methods will it match?

medium

A. All methods named 'find' in any class in com.example.repo

B. All public methods starting with 'find' in any class ending with 'Repository' in package com.example.repo

C. All public methods in any class in com.example.repo

D. Only methods named exactly 'find' in any class ending with 'Repository'

Solution

1. Step 1: Break down the expression

   public * means any public return type, com.example.repo.*Repository matches classes ending with 'Repository' in the package, and find*(..) matches methods starting with 'find' with any parameters.

2. Step 2: Match options to expression meaning

   All public methods starting with 'find' in any class ending with 'Repository' in package com.example.repo correctly describes all public methods starting with 'find' in classes ending with 'Repository' in the package. Others are either too broad or too narrow.

3. Final Answer:

   All public methods starting with 'find' in any class ending with 'Repository' in package com.example.repo -> Option B

4. Quick Check:

   execution(public * com.example.repo.*Repository.find*(..)) = All public methods starting with 'find' in any class ending with 'Repository' in package com.example.repo [OK]

Hint: Look for wildcards * and method name patterns carefully [OK]

Common Mistakes:

• Ignoring method name prefix 'find*'
• Confusing class name pattern *Repository
• Missing public modifier effect

4. Identify the error in this pointcut expression: execution(* com.example..service.*(..)

medium

A. Missing closing parenthesis at the end

B. Incorrect use of double dots '..' in package name

C. Wildcard '*' cannot be used for method names

D. Return type '*' is invalid

Solution

1. Step 1: Check syntax completeness

   The expression is missing a closing parenthesis ')' at the end, which is required to close the execution() expression.

2. Step 2: Validate other parts

   Double dots '..' are valid to match subpackages, '*' is valid for method names, and '*' is valid for return type.

3. Final Answer:

   Missing closing parenthesis at the end -> Option A

4. Quick Check:

   Check parentheses balance in execution() [OK]

Hint: Count parentheses carefully in pointcut expressions [OK]

Common Mistakes:

• Forgetting closing parenthesis
• Misunderstanding '..' usage
• Thinking '*' is invalid for methods or return types

5. You want to create a pointcut expression that matches all methods in any class within com.app.service and its subpackages, but only methods that have exactly two parameters of any type. Which expression is correct?

hard

A. execution(* com.app.service..*.*(*, *))

B. execution(* com.app.service.*.*(..))

C. execution(* com.app.service..*.*(.., ..))

D. execution(* com.app.service..*.*(*))

Solution

1. Step 1: Understand package and subpackage matching

   com.app.service..* matches classes in the package and all subpackages.

2. Step 2: Match method parameters exactly

   (* , *) means exactly two parameters of any type. (..) means any number of parameters, so it's incorrect here.

3. Step 3: Analyze options

   execution(* com.app.service..*.*(*, *)) correctly matches all classes in package and subpackages with exactly two parameters. Others either match any number of parameters or wrong parameter counts.

4. Final Answer:

   execution(* com.app.service..*.*(*, *)) -> Option A

5. Quick Check:

   Use (*, *) for exactly two parameters [OK]

Hint: Use (*, *) to match exactly two parameters [OK]

Common Mistakes:

• Using (..) to match exact parameter count
• Confusing single * with .. for subpackages
• Missing commas between parameters