How can I validate a collection of string and each element as a URL?

Question

I want to validate URLs in a Collection<String>. Each element is a URL that I get as a string in the form.

@Valid
@URL
@ElementCollection 
public Collection<String> getPictures() {       
    return this.pictures;   
}

public void setPictures(final Collection<String> pictures) {         
      this.pictures = pictures;     
}

I want to know if there is some annotation in Spring that allows me to validate all the strings in this collection like URLs

Answer 1

There is no annotation that validates the field directly. The idea of a custom annotation @URL is perfectly valid, yet you have to implement the validation itself - the annotation is just a mark that "something should happen with this".

I suggest you rename @URL to @URLCollection to avoid conflict with the class java.net.URL. Start with defining the annotation. Don't forget to the annotation @Constraint (look at its documentation to learn how to define the custom validation annotation properly):

@Target({ElementType.METHOD, ElementType.FIELD})
@Retention(RetentionPolicy.RUNTIME)
@Constraint(validatedBy = UrlCollectionValidator.class)     // will be created below
public @interface URLCollection {
    String message() default "default error message";
    Class<?>[] groups() default {};
    Class<? extends Payload>[] payload() default {};
}

Then continue with the implementation of ConstraintValidator:

public class UrlCollectionValidator implements ConstraintValidator<URLCollection, Collection<String>> {

    @Override
    public void initialize(URLCollectionconstraint) { }

    @Override
    public boolean isValid(Collection<String> urls, ConstraintValidatorContext context) {
        return // the validation logics
    }
}

Well, that's all. Read more about this at Configuring Custom Constraints at the Spring documentation:

Each bean validation constraint consists of two parts: * A @Constraint annotation that declares the constraint and its configurable properties. * An implementation of the javax.validation.ConstraintValidator interface that implements the constraint’s behavior.