Custom validator annotation in Spring Boot - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to define a custom annotation for validation.

Spring Boot

public @interface [1] {
    String message() default "Invalid value";
    Class<?>[] groups() default {};
    Class<? extends Payload>[] payload() default {};
}

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ACustomValidator

BConstraint

CValidCustom

DMyValidator

Attempts:

3 left

💡 Hint

Common Mistakes

Using generic names like 'Constraint' which is a meta-annotation, not a custom annotation name.

Using names that do not start with 'Valid' which is a common convention.

The annotation name should be descriptive and typically starts with 'Valid' for validators. Here, ValidCustom is a good choice.

2fill in blank

medium

Complete the code to add the correct meta-annotation to define a custom validator annotation.

Spring Boot

@[1](validatedBy = CustomValidator.class)
public @interface ValidCustom {
    String message() default "Invalid value";
    Class<?>[] groups() default {};
    Class<? extends Payload>[] payload() default {};
}

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AConstraint

BTarget

CRetention

DDocumented

Attempts:

3 left

💡 Hint

Common Mistakes

Using @Target or @Retention instead of @Constraint for linking validator.

Omitting the validatedBy attribute.

The @Constraint annotation is required to specify the validator class for a custom validation annotation.

3fill in blank

hard

Fix the error in the validator class by completing the method signature correctly.

Spring Boot

public class CustomValidator implements ConstraintValidator<ValidCustom, String> {
    @Override
    public boolean [1](String value, ConstraintValidatorContext context) {
        return value != null && value.matches("^[a-zA-Z]+$");
    }
}

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Avalidate

BisValid

Ccheck

DvalidateValue

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'validate' or 'check' which are not the correct method names.

Incorrect method signature causing compile errors.

The method to override in ConstraintValidator is isValid.

4fill in blank

hard

Fill both blanks to specify where the custom annotation can be applied and its retention policy.

Spring Boot

@Target([1])
@Retention([2])
@Constraint(validatedBy = CustomValidator.class)
public @interface ValidCustom {
    String message() default "Invalid value";
    Class<?>[] groups() default {};
    Class<? extends Payload>[] payload() default {};
}

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AElementType.FIELD

BElementType.METHOD

CRetentionPolicy.RUNTIME

DRetentionPolicy.CLASS

Attempts:

3 left

💡 Hint

Common Mistakes

Using RetentionPolicy.CLASS which is not available at runtime.

Targeting methods only when fields are intended.

The annotation should be applied to fields, so ElementType.FIELD is correct. The retention must be RUNTIME so it is available during runtime for validation.

5fill in blank

hard

Fill all three blanks to create a map of field names to their lengths for words longer than 3 characters.

Spring Boot

Map<String, Integer> lengths = words.stream()
    .filter(word -> word.length() [1] 3)
    .collect(Collectors.toMap(
        word -> word.[2](),
        word -> word.[3]()
    ));

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A>

Blength

D<

Attempts:

3 left

💡 Hint

Common Mistakes

Using '<' instead of '>' in the filter.

Using incorrect methods for key or value mapping.

The filter checks for words longer than 3 characters using '>'. The key mapper uses 'length' (assuming a method to get a key, but here it should be word itself or word.toString(), but for this exercise we accept 'length' as a placeholder). The value mapper uses 'length' to get the length of the word.