@Email and @Pattern in Spring Boot - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ component_behavior

intermediate

What happens when @Email validation fails?

Consider a Spring Boot REST controller receiving a user email annotated with @Email. What is the typical behavior when the email format is invalid?

Spring Boot

public class User {
    @Email
    private String email;

    // getters and setters
}

@PostMapping("/register")
public ResponseEntity<String> registerUser(@Valid @RequestBody User user) {
    return ResponseEntity.ok("User registered");
}

A A validation error is thrown and the request returns a 400 Bad Request response automatically.

B The controller method executes normally and saves the user with the invalid email.

C The application crashes with a NullPointerException.

D The invalid email is automatically corrected to a valid format.

💡 Hint

Think about how Spring Boot handles validation annotations with @Valid.

The @Email annotation triggers validation on the email field. When used with @Valid in the controller, Spring Boot automatically checks the input. If the email is invalid, it returns a 400 Bad Request with validation error details.

📝 Syntax

intermediate

Which @Pattern regex correctly validates a 5-digit US ZIP code?

You want to validate a US ZIP code that must be exactly 5 digits using @Pattern. Which regex pattern is correct?

Spring Boot

public class Address {
    @Pattern(regexp = "???", message = "Invalid ZIP code")
    private String zipCode;

    // getters and setters
}

A "[a-zA-Z]{5}"

B "\d{5,}"

C "\\d{5}"

D "[0-9]{4}"

💡 Hint

Remember to escape backslashes in Java strings.

The regex "\\d{5}" matches exactly 5 digits. The double backslash is needed in Java strings to represent a single backslash in the regex.

🔧 Debug

advanced

Why does this @Email validation not work as expected?

Given this code snippet, why does the @Email annotation not trigger validation errors for invalid emails?

Spring Boot

public class Contact {
    @Email
    private String email;

    // getters and setters
}

@PostMapping("/contact")
public String submitContact(@RequestBody Contact contact) {
    return "Received";
}

A Because the @Email annotation requires a custom validator bean to be registered.

B Because @Email only works on fields of type java.net.Email, not String.

C Because the email field is private and needs to be public for validation.

D Because @Valid is missing on the controller method parameter, so validation is not triggered.

💡 Hint

Check how validation is triggered in Spring Boot controllers.

Validation annotations like @Email require the @Valid annotation on the controller method parameter to activate validation. Without @Valid, the annotations are ignored.

🧠 Conceptual

advanced

How does @Pattern differ from @Email in validation?

Which statement best describes the difference between @Pattern and @Email annotations in Spring Boot validation?

A @Email validates only email format, while @Pattern can validate any string against a custom regex.

B @Pattern validates email format, while @Email validates phone numbers.

C @Email and @Pattern are interchangeable and validate the same patterns.

D @Pattern automatically fixes invalid input, @Email only reports errors.

💡 Hint

Think about the purpose of each annotation.

@Email is a specialized annotation for email format validation. @Pattern is a general-purpose annotation that validates strings against any regex pattern you provide.

❓ state_output

expert

What is the validation error message when @Pattern fails?

Given this code snippet, what exact message will be returned if the zipCode does not match the pattern?

Spring Boot

public class Location {
    @Pattern(regexp = "\\d{5}", message = "ZIP code must be 5 digits")
    private String zipCode;

    // getters and setters
}

@PostMapping("/location")
public ResponseEntity<String> addLocation(@Valid @RequestBody Location location) {
    return ResponseEntity.ok("Location added");
}

A "Invalid ZIP code format"

B "ZIP code must be 5 digits"

C "zipCode does not match pattern"

D "Validation failed for zipCode"

💡 Hint

Look at the message attribute in the @Pattern annotation.

The message attribute in @Pattern defines the exact error message returned when validation fails.