Custom bean validator does not autowire service

Question

I'm a little bit at a loss what I'm missing, I have following custom bean validator code:

import jakarta.validation.Payload;

import java.lang.annotation.ElementType;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;

@Constraint(validatedBy=UniqueCarBrandNameValidator.class)
@Target(ElementType.FIELD)
@Retention(RetentionPolicy.RUNTIME)
public @interface UniqueCarBrandName {
    String message() default "Email address is already registered";
    Class<?>[] groups() default { };
    Class<? extends Payload>[] payload() default { };
}

import icodeit.carfleetmanager.service.CarBrandService;
import jakarta.validation.ConstraintValidator;
import jakarta.validation.ConstraintValidatorContext;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Component;

@Component
public class UniqueCarBrandNameValidator implements ConstraintValidator<UniqueCarBrandName, String> {

    @Autowired
    private CarBrandService carBrandService;

    @Override
    public boolean isValid(String name, ConstraintValidatorContext constraintValidatorContext) {
        return carBrandService.fetchOneByName(name).isEmpty();
    }
}

In short I need a service to see if my CarBrandName is unique or not and I tried to implement this in a custom validator annotation. Problem is auto-wiring does not work in the custom validator, the service is null, giving me an NPE but the service works just fine auto-wired in my controller. Following the documentation I have included following configuration:

import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
import org.springframework.validation.Validator;
import org.springframework.validation.beanvalidation.LocalValidatorFactoryBean;
import org.springframework.validation.beanvalidation.MethodValidationPostProcessor;

@Configuration
public class AppConfig {

    // Used for auto wiring beans in validation classes
    @Bean
    public Validator validator() {
        return new LocalValidatorFactoryBean();
    }

    @Bean
    public MethodValidationPostProcessor validationPostProcessor() {
        return new MethodValidationPostProcessor();
    }
}

So that the Spring context is also available in the custom validator. But to no avail. I also tried the proposed solutions in this stackoverflow thread but none worked.

I'm using following maven config:

?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 https://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>
    <parent>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-parent</artifactId>
        <version>3.0.5</version>
        <relativePath/> <!-- lookup parent from repository -->
    </parent>
    <groupId>icodeit</groupId>
    <artifactId>service</artifactId>
    <version>0.0.1-SNAPSHOT</version>
    <name>service</name>
    <description>backend service</description>
    <properties>
        <java.version>17</java.version>
        <jackson-hibernate.version>2.15.0-rc2</jackson-hibernate.version>
        <org.mapstruct.version>1.5.4.Final</org.mapstruct.version>
        <lombok-mapstruct-binding.version>0.2.0</lombok-mapstruct-binding.version>
        <lombok.version>1.18.24</lombok.version>
    </properties>
    <dependencies>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-data-jpa</artifactId>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-jdbc</artifactId>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-validation</artifactId>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-web</artifactId>
        </dependency>
        <dependency>
            <groupId>org.liquibase</groupId>
            <artifactId>liquibase-core</artifactId>
        </dependency>

        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-devtools</artifactId>
            <scope>runtime</scope>
            <optional>true</optional>
        </dependency>
        <dependency>
            <groupId>com.h2database</groupId>
            <artifactId>h2</artifactId>
            <scope>runtime</scope>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-test</artifactId>
            <scope>test</scope>
        </dependency>
        <dependency>
            <groupId>org.mapstruct</groupId>
            <artifactId>mapstruct</artifactId>
            <version>${org.mapstruct.version}</version>
        </dependency>
        <dependency>
            <groupId>org.projectlombok</groupId>
            <artifactId>lombok-mapstruct-binding</artifactId>
            <version>${lombok-mapstruct-binding.version}</version>
        </dependency>
        <dependency>
            <groupId>org.projectlombok</groupId>
            <artifactId>lombok</artifactId>
            <version>${lombok.version}</version>
            <optional>true</optional>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-oauth2-client</artifactId>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-security</artifactId>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-oauth2-resource-server</artifactId>
        </dependency>
        <dependency>
            <groupId>org.springframework.security</groupId>
            <artifactId>spring-security-test</artifactId>
            <scope>test</scope>
        </dependency>
    </dependencies>


</project>

Relevant error message:

java.lang.NullPointerException: Cannot invoke "icodeit.carfleetmanager.service.CarBrandService.fetchOneByName(String)" because "this.carBrandService" is null
    at icodeit.carfleetmanager.validation.carbrand.UniqueCarBrandNameValidator.isValid(UniqueCarBrandNameValidator.java:17) ~[classes/:na]
    at icodeit.carfleetmanager.validation.carbrand.UniqueCarBrandNameValidator.isValid(UniqueCarBrandNameValidator.java:9) ~[classes/:na]
    at org.hibernate.validator.internal.engine.constraintvalidation.ConstraintTree.validateSingleConstraint(ConstraintTree.java:180) ~[hibernate-validator-8.0.0.Final.jar:8.0.0.Final]
    at org.hibernate.validator.internal.engine.constraintvalidation.SimpleConstraintTree.validateConstraints(SimpleConstraintTree.java:66) ~[hibernate-validator-8.0.0.Final.jar:8.0.0.Final]
    at org.hibernate.validator.internal.engine.constraintvalidation.ConstraintTree.validateConstraints(ConstraintTree.java:75) ~[hibernate-validator-8.0.0.Final.jar:8.0.0.Final]
    at org.hibernate.validator.internal.metadata.core.MetaConstraint.doValidateConstraint(MetaConstraint.java:130) ~[hibernate-validator-8.0.0.Final.jar:8.0.0.Final]
    at org.hibernate.validator.internal.metadata.core.MetaConstraint.validateConstraint(MetaConstraint.java:123) ~[hibernate-validator-8.0.0.Final.jar:8.0.0.Final]
    at org.hibernate.validator.internal.engine.ValidatorImpl.validateMetaConstraint(ValidatorImpl.java:555) ~[hibernate-validator-8.0.0.Final.jar:8.0.0.Final]
    at org.hibernate.validator.internal.engine.ValidatorImpl.validateConstraintsForSingleDefaultGroupElement(ValidatorImpl.java:518) ~[hibernate-validator-8.0.0.Final.jar:8.0.0.Final]
    at org.hibernate.validator.internal.engine.ValidatorImpl.validateConstraintsForDefaultGroup(ValidatorImpl.java:488) ~[hibernate-validator-8.0.0.Final.jar:8.0.0.Final]
    at org.hibernate.validator.internal.engine.ValidatorImpl.validateConstraintsForCurrentGroup(ValidatorImpl.java:450) ~[hibernate-validator-8.0.0.Final.jar:8.0.0.Final]
    at org.hibernate.validator.internal.engine.ValidatorImpl.validateInContext(ValidatorImpl.java:400) ~[hibernate-validator-8.0.0.Final.jar:8.0.0.Final]
    at org.hibernate.validator.internal.engine.ValidatorImpl.validate(ValidatorImpl.java:172) ~[hibernate-validator-8.0.0.Final.jar:8.0.0.Final]
    at org.hibernate.cfg.beanvalidation.BeanValidationEventListener.validate(BeanValidationEventListener.java:125) ~[hibernate-core-6.1.7.Final.jar:6.1.7.Final]
    at org.hibernate.cfg.beanvalidation.BeanValidationEventListener.onPreInsert(BeanValidationEventListener.java:80) ~[hibernate-core-6.1.7.Final.jar:6.1.7.Final]
    at org.hibernate.action.internal.EntityIdentityInsertAction.preInsert(EntityIdentityInsertAction.java:184) ~[hibernate-core-6.1.7.Final.jar:6.1.7.Final]
    at org.hibernate.action.internal.EntityIdentityInsertAction.execute(EntityIdentityInsertAction.java:74) ~[hibernate-core-6.1.7.Final.jar:6.1.7.Final]
    at org.hibernate.engine.spi.ActionQueue.execute(ActionQueue.java:653) ~[hibernate-core-6.1.7.Final.jar:6.1.7.Final]
    at org.hibernate.engine.spi.ActionQueue.addResolvedEntityInsertAction(ActionQueue.java:283) ~[hibernate-core-6.1.7.Final.jar:6.1.7.Final]
    at org.hibernate.engine.spi.ActionQueue.addInsertAction(ActionQueue.java:264) ~[hibernate-core-6.1.7.Final.jar:6.1.7.Final]
    at org.hibernate.engine.spi.ActionQueue.addAction(ActionQueue.java:322) ~[hibernate-core-6.1.7.Final.jar:6.1.7.Final]
    at org.hibernate.event.internal.AbstractSaveEventListener.addInsertAction(AbstractSaveEventListener.java:340) ~[hibernate-core-6.1.7.Final.jar:6.1.7.Final]
    at org.hibernate.event.internal.AbstractSaveEventListener.performSaveOrReplicate(AbstractSaveEventListener.java:286) ~[hibernate-core-6.1.7.Final.jar:6.1.7.Final]
    at org.hibernate.event.internal.AbstractSaveEventListener.performSave(AbstractSaveEventListener.java:192) ~[hibernate-core-6.1.7.Final.jar:6.1.7.Final]
    at org.hibernate.event.internal.AbstractSaveEventListener.saveWithGeneratedId(AbstractSaveEventListener.java:122) ~[hibernate-core-6.1.7.Final.jar:6.1.7.Final]
    at org.hibernate.event.internal.DefaultPersistEventListener.entityIsTransient(DefaultPersistEventListener.java:184) ~[hibernate-core-6.1.7.Final.jar:6.1.7.Final]
    at org.hibernate.event.internal.DefaultPersistEventListener.onPersist(DefaultPersistEventListener.java:129) ~[hibernate-core-6.1.7.Final.jar:6.1.7.Final]
    at org.hibernate.event.internal.DefaultPersistEventListener.onPersist(DefaultPersistEventListener.java:53) ~[hibernate-core-6.1.7.Final.jar:6.1.7.Final]
    at org.hibernate.event.service.internal.EventListenerGroupImpl.fireEventOnEachListener(EventListenerGroupImpl.java:107) ~[hibernate-core-6.1.7.Final.jar:6.1.7.Final]
    at org.hibernate.internal.SessionImpl.firePersist(SessionImpl.java:737) ~[hibernate-core-6.1.7.Final.jar:6.1.7.Final]
    at org.hibernate.internal.SessionImpl.persist(SessionImpl.java:721) ~[hibernate-core-6.1.7.Final.jar:6.1.7.Final]
    at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method) ~[na:na]

Edit: I have tried by using injecting via the constructor as advised in an answer by ananta, but sadly I get following error:

java.lang.NoSuchMethodException: icodeit.carfleetmanager.validation.carbrand.UniqueCarBrandNameValidator.<init>()
    at java.base/java.lang.Class.getConstructor0(Class.java:3585) ~[na:na]
    at java.base/java.lang.Class.getConstructor(Class.java:2271) ~[na:na]

Answer 1

You can try @AllArgsConstructor to inject CarBrandService instead of @Autowire. Using this way, the bean container will have to make sure your CarBrandService is existed before creating UniqueCarBrandNameValidator, otherwise, it will break in starup.

@Component
@AllArgsConstructor // Add this
public class UniqueCarBrandNameValidator implements ConstraintValidator<UniqueCarBrandName, String> {

    // @Autowired => Remove this
    private CarBrandService carBrandService;
    ...
}

Answer 2

I think I found a possible solution, while trying things out. It works, if you use an alternative method by validating your entity in an service by using the injected Validator by Jakarta and then see that your entity doesn't validate while submitting it to the JPA repository:

@AllArgsConstructor
@Component
public class CarBrandService {

    private final CarBrandRepository carBrandRepository;
    private final Validator validator;
...
    private void validate(CarBrand carBrand) {
        // This works!!
        Set<ConstraintViolation<CarBrand>> constraintViolations = validator.validate(carBrand);
        if (!customConstraintVoilations.isEmpty() || !constraintViolations.isEmpty()) {
            throw new CustomConstraintViolationException(customConstraintVoilations, constraintViolations);
        }
    }
... 

Only problem now is that on save it again will get validated and in this case it will again throw the NPE error. You can solve this by doing validation on another object than the entity.