Master Bean Validation in Spring 5: From Basics to Custom Constraints

Overview

Bean Validation offers a universal way to validate Java applications by declaring constraints on domain model properties. The runtime enforces these constraints. Built‑in constraints are available, and you can define custom ones. Example:

<code>public class User {
    @NotEmpty(message = "姓名不能为空")
    private String name;
    @Min(value = 1, message = "年龄必须大于1")
    private Integer age;
}</code>

The Bean Validation validator then checks instances of this class. For general API information see https://beanvalidation.org/ and for specific constraints refer to the Hibernate Validator documentation at https://hibernate.org/validator/ .

Configuring the Validation Provider

Spring fully supports the Bean Validation API and allows the validator provider to be configured as a Spring bean. You can expose javax.validation.ValidatorFactory or javax.validation.Validator for injection.

Use LocalValidatorFactoryBean to register the default validator:

<code>import org.springframework.validation.beanvalidation.LocalValidatorFactoryBean;

@Configuration
public class AppConfig {
    @Bean
    public LocalValidatorFactoryBean validator() {
        return new LocalValidatorFactoryBean();
    }
}</code>

This basic configuration automatically triggers bean validation initialization. Ensure a Bean Validation provider (e.g., Hibernate Validator) is on the classpath.

Injecting the Validator

LocalValidatorFactoryBean implements javax.validation.ValidatorFactory , javax.validation.Validator , and Spring’s org.springframework.validation.Validator . You can inject any of these interfaces into beans that need validation logic.

Direct injection of the Bean Validation API:

<code>import javax.validation.Validator;

@Service
public class MyService {
    @Autowired
    private Validator validator;
}</code>

Or inject Spring’s org.springframework.validation.Validator :

<code>import org.springframework.validation.Validator;

@Service
public class MyService {
    @Autowired
    private Validator validator;
}</code>

Custom Validation

Define a custom annotation:

<code>@Documented
@Constraint(validatedBy = ValidEmptyConstraintValidator.class)
@Target({ METHOD, FIELD, ANNOTATION_TYPE, CONSTRUCTOR, PARAMETER, TYPE_USE })
@Retention(RUNTIME)
public @interface ValidEmpty {
    String message() default "";
    Class<?>[] groups() default {};
    Class<? extends Payload>[] payload() default {};
}</code>

Implement the validation logic:

<code>@Component
@SuppressWarnings("rawtypes")
public class ValidEmptyConstraintValidator implements ConstraintValidator<ValidEmpty, Collection> {
    @Override
    public boolean isValid(Collection value, ConstraintValidatorContext context) {
        return !(value == null || value.isEmpty());
    }
}</code>

Use the custom constraint on a field:

<code>@ValidEmpty(message = "集合不能为空")
private List<String> list;</code>

Method Parameter and Return‑Value Validation

Enable method‑level validation by registering MethodValidationPostProcessor :

<code>@Configuration
public class AppConfig {
    @Bean
    public MethodValidationPostProcessor validationPostProcessor() {
        return new MethodValidationPostProcessor();
    }
}</code>

Annotate target classes with @Validated and place constraint annotations on method parameters:

<code>public class User {
    @NotEmpty(message = "姓名不能为空")
    private String name;
    private Integer age;
}

@Validated
public class UserService {
    public void findById(@NotNull(message = "ID不能为空") Long id) {
        // ...
    }
}</code>

Register the beans and invoke the service:

<code>GenericApplicationContext context = new GenericApplicationContext();
AnnotatedBeanDefinitionReader reader = new AnnotatedBeanDefinitionReader(context);
reader.registerBean(MethodValidationPostProcessor.class);
reader.registerBean(UserService.class);
context.refresh();
UserService us = context.getBean(UserService.class);
User user = new User();
us.save(user);
us.findById(null);
context.close();</code>

Resulting exception:

<code>Exception in thread "main" javax.validation.ConstraintViolationException: findById.arg0: ID不能为空
    at org.springframework.validation.beanvalidation.MethodValidationInterceptor.invoke(MethodValidationInterceptor.java:120)
    ...</code>

All steps demonstrate how to set up Bean Validation in Spring, inject validators, create custom constraints, and apply method‑level validation.