Spring Framework - Creating Custom Validation Annotation Examples

package com.logicbig.example;

import jakarta.validation.Constraint;
import jakarta.validation.Payload;
import java.lang.annotation.*;

@Target({ElementType.FIELD, ElementType.METHOD, ElementType.PARAMETER,
        ElementType.ANNOTATION_TYPE})
@Retention(RetentionPolicy.RUNTIME)
@Constraint(validatedBy = LanguageValidator.class)
public @interface Language {

    String message() default "must be a valid language display name," +
            " found: ${validatedValue}";

    Class<?>[] groups() default {};

    Class<? extends Payload>[] payload() default {};
}

package com.logicbig.example;

import org.springframework.beans.factory.annotation.Autowired;
import jakarta.validation.ConstraintValidator;
import jakarta.validation.ConstraintValidatorContext;

public class LanguageValidator implements ConstraintValidator<Language, String> {
    @Autowired
    private LanguageProvider languageProvider;

    @Override
    public void initialize(Language constraintAnnotation) {
    }

    @Override
    public boolean isValid(String value, ConstraintValidatorContext context) {
        if (value == null) {
            return false;
        }
        return languageProvider.getLanguages()
                               .stream()
                               .anyMatch(value::equalsIgnoreCase);
    }
}

package com.logicbig.example;

import org.springframework.stereotype.Component;
import java.util.ArrayList;
import java.util.List;
import java.util.Locale;

public interface LanguageProvider {

    List<String> getLanguages();

    @Component
    public static class DefaultLanguageProvider implements LanguageProvider {

        @Override
        public List<String> getLanguages() {
            List<String> languageList = new ArrayList<>();
            for (Locale locale : Locale.getAvailableLocales()) {
                languageList.add(locale.getDisplayLanguage());
            }
            return languageList;
        }
    }
}

package com.logicbig.example;

import jakarta.validation.constraints.NotNull;

public class Book {
    @NotNull
    private String name;
    @Language
    private String language;

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public String getLanguage() {
        return language;
    }

    public void setLanguage(String language) {
        this.language = language;
    }
}

package com.logicbig.example;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Component;
import jakarta.validation.ConstraintViolation;
import jakarta.validation.Validator;
import java.util.Set;

@Component
public class ClientBean {
    @Autowired
    private Validator validator;

    public void run() {
        Book book = new Book();
        book.setName("Alien Explorer");
        book.setLanguage("Englis");

        Set<ConstraintViolation<Book>> c = validator.validate(book);
        if (c.size() > 0) {
            System.err.println("validation errors:");
            c.stream().map(v -> v.getMessage()).forEach(System.err::println);
        }
    }
}

package com.logicbig.example;

import org.springframework.context.annotation.AnnotationConfigApplicationContext;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.ComponentScan;
import org.springframework.context.annotation.Configuration;
import org.springframework.validation.beanvalidation.LocalValidatorFactoryBean;
import jakarta.validation.Validator;

@Configuration
@ComponentScan
public class AppConfig {
    @Bean
    public Validator validatorFactory() {
        return new LocalValidatorFactoryBean();
    }

    public static void main(String[] args) {
        AnnotationConfigApplicationContext context =
                new AnnotationConfigApplicationContext(
                        AppConfig.class);

        ClientBean bean = context.getBean(ClientBean.class);
        bean.run();
    }
}