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Custom declarative spring pojo validation during deserialization of request

I am looking for annotation to annotate pojo class which I need to validate during request deserialization. I am searching for annotation to pass as parameter class which will validate my pojo.
Implementation can look like that:
#ValidateAnnotation(class = ExampleClassValidator.class)
public class ExampleClass {
private String name;
}
Has anyone know any of spring annotation for that approach or some dependency which offer that declarative validation ? I am asking because I cannot find any similar solution in documentation.

You can use #InitBinder to configure a validator based on the target of the method. Here's a simple example:
Annotation class:
package test.xyz;
import org.springframework.validation.Validator;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
#Retention(RetentionPolicy.RUNTIME)
public #interface ValidateAnnotation {
Class<? extends Validator> value();
}
The example class to be validated:
package test.xyz;
#ValidateAnnotation(ExampleClassValidator.class)
public class ExampleClass {
}
The validator class:
package test.xyz;
import org.springframework.validation.Errors;
public class ExampleClassValidator implements org.springframework.validation.Validator {
#Override
public boolean supports(Class<?> aClass) {
return ExampleClass.class.isAssignableFrom(aClass);
}
#Override
public void validate(Object o, Errors errors) {
}
}
And finally the controller class with the #InitBinder definition:
import org.springframework.stereotype.Controller;
import org.springframework.validation.Errors;
import org.springframework.validation.Validator;
import org.springframework.web.bind.WebDataBinder;
import org.springframework.web.bind.annotation.InitBinder;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RequestMethod;
import org.springframework.web.bind.annotation.ResponseBody;
import test.xyz.ExampleClass;
import test.xyz.ValidateAnnotation;
import javax.servlet.http.HttpServletRequest;
import javax.validation.Valid;
import java.util.Collections;
#Controller
public class ExampleController {
#RequestMapping(value="test-endpoint", method= RequestMethod.GET)
public #ResponseBody
Object testMethod(#Valid ExampleClass exampleClass, Errors errors) {
return Collections.singletonMap("success", true);
}
#InitBinder
public void initBinder(WebDataBinder binder, HttpServletRequest request) throws IllegalAccessException, InstantiationException {
Class<?> targetClass = binder.getTarget().getClass();
if(targetClass.isAnnotationPresent(ValidateAnnotation.class)) {
ValidateAnnotation annotation = targetClass.getAnnotation(ValidateAnnotation.class);
Class<? extends Validator> value = annotation.value();
Validator validator = value.newInstance();
binder.setValidator(validator);
}
}
}
Explanation:
You can use the WebDataBinder's getTarget method to access the target to be validated. From there it is straightforward to check the annotation on the class, get the validator class, and set it on the binder. I believe you can also use the #ControllerAdvice annotation to configure a global InitBinder. As a disclaimer, I don't know if it is recommended to access the binder target within the InitBinder, but I haven't had any issues the few times I've done so.

For normal validation you can annotate your class with the annotations from the javax.validation.constraints package, like javax.validation.constraints.NotEmpty. For custom validation, you can make your own annotation that will call a custom validator that you write.
For example, if you wanted to create a validator that makes sure a field is nine characters long you could do the following:
First, create your custom validation annotation.
#Documented
#Constraint(validatedBy = NineCharactersValidator.class)
#Target( { ElementType.METHOD, ElementType.FIELD })
#Retention(RetentionPolicy.RUNTIME)
public #interface NineCharactersOnly {
String message() default "This field must contain exactly nine characters";
Class<?>[] groups() default {};
Class<? extends Payload>[] payload() default {};
}
Next, create your custom validator:
public class NineCharactersValidator implements ConstraintValidator<NineCharactersOnly, String> {
#Override
public void initialize(NineCharactersOnly contactNumber) {
}
#Override
public boolean isValid(String contactField, ConstraintValidatorContext cxt) {
return contactField != null && contactField.length() == 9;
}
}
Next, use the annotation on fields that need to be constrained on your pojo.
public class ExampleClass {
#NineCharactersOnly
private String fieldThatMustBeNineCharacters;
}
Next, mark your method parameters in the controller with #Valid so they will be validated by Spring:
#RestController
public class CustomValidationController {
#PostMapping("/customValidationPost")
public ResponseEntity<String> customValidation(#Valid ExampleClass exampleClass, BindingResult result, Model m) {
// we know the data is valid if we get this far because Spring automatically validates the input and
// throws a MethodArgumentNotValidException if it's invalid and returns an HTTP response of 400 (Bad Request).
return ResponseEntity.ok("Data is valid");
}
}
Finally, if you want custom logic for handling validation errors instead of just sending a 400, you can create a custom validation handler method.
#ResponseStatus(HttpStatus.BAD_REQUEST)
#ExceptionHandler(MethodArgumentNotValidException.class)
public Map<String, String> handleValidationException(MethodArgumentNotValidException e) {
Map<String, String> errors = new HashMap<>();
d.getBindingResult().getAllErrors().forEach((error) -> {
String fieldName = ((FieldError) error).getField();
String errorMessage = error.getDefaultMessage();
errors.put(fieldName, errorMessage);
});
return errors;
}

Maybe writing your custom annotation and using Spring AOP will help you. Spring AOP is quite simple.

I found pretty good solution but in one place i used reflection :(
Please feel free to comment and rate this solution, is it good enough or something could be done better.
I had create own annotation
#Retention(RetentionPolicy.RUNTIME)
#Target(ElementType.TYPE)
public #interface Validator {
Class<? extends org.springframework.validation.Validator> validator();
}
I next step I extend LocalValidatorFactoryBean to override validate method and here I was forced to use reflection to get class from annotation.
#Component
#RequiredArgsConstructor
class CustomLocalValidatorFactoryBean extends LocalValidatorFactoryBean {
private final Map<Class<? extends Validator>, Validator> validators;
#Override
public void validate(Object target, Errors errors, Object... validationHints) {
Class<? extends Validator> validatorKey = target.getClass().getAnnotation(com.validation.validator.Validator.class).validator();
Optional.ofNullable(validators.get(validatorKey)).ifPresentOrElse(
validator ->
validator.validate(target, errors),
() -> super.validate(target, errors, validationHints)
);
}
}
I annotate pojo with my annotation to specify validator.
#Data
#Validator(validator = PersonValidator.class)
public class PersonDto {
private final String name;
private final String surname;
private final Integer age;
}
As you can see in my CustomLocalValidatorFactoryBean I injected a map of validators, in this map i store validators assigned to key which is the class of this validator. This class i specify in annotation in pojo to fetch suitable validator for currect validate target. And this is my configuration of validatos map.
#Configuration
class ValidatorConfig {
#Bean
Map<Class<? extends Validator>, Validator> validators() {
var validators = new HashMap<Class<? extends Validator>, Validator>();
validators.put(PersonValidator.class, new PersonValidator());
return validators;
}
}
I specify custom #RestControllerAdvice and override method handleMethodArgumentNotValid.
#RestControllerAdvice
class GlobalExceptionHandler extends ResponseEntityExceptionHandler {
#Override
protected ResponseEntity<Object> handleMethodArgumentNotValid(MethodArgumentNotValidException ex, HttpHeaders headers,
HttpStatus status, WebRequest request) {
Map<String, String> errors = new HashMap<>();
ex.getBindingResult().getAllErrors().forEach((error) -> {
String fieldName = error.getCode();
String errorMessage = error.getDefaultMessage();
errors.put(fieldName, errorMessage);
});
return new ResponseEntity<>(errors, HttpStatus.BAD_REQUEST);
}
}
And this is my validator, it could be bean with dao acces but it could also be simple pojo.
public class PersonValidator implements Validator {
#Override
public boolean supports(Class<?> aClass) {
return PersonDto.class.isAssignableFrom(aClass);
}
#Override
public void validate(Object object, Errors errors) {
Optional.of(object).map(obj -> (PersonDto) obj).ifPresent(person -> {
Optional.ofNullable(person.getName())
.filter(name -> Strings.isNotBlank(name) && name.length() >= 3)
.ifPresentOrElse(name -> doNothing(), () -> errors.reject("person.name", "name of person is invalid!"));
});
}
}
What do you think about that configuration, is it cannon on sparrow or you just like that solution ?

How to confirgure swagger to handle custom Controller-level PathVariable annotations?

In my Spring (4.3.2) project I'm using Swagger (2.7.0) to automatically generate docs and swagger-ui for my project. This worked great so far.
But now I determined that I need to be able to declare Path Variables at the Controller level (not method level). And I need to teach swagger to discover these path variables and add them to docs and swagger-ui.
I've created custom annotation
#Target(ElementType.TYPE)
#Retention(RetentionPolicy.RUNTIME)
public #interface HasCommonPathVariable {
/**
* The URI template variable to bind to.
*/
String name();
Class<?> type();
String defaultValue() default "";
}
And I'm using it like this:
#RestController
#Secured(SecurityConstants.ROLE_USER)
#RequestMapping(path = "/rest/api/v1/env/{envId}/asset-type")
#HasCommonPathVariable(name = "envId", type = Long.class)
public class AssetTypeRestController extends CustomRestControllerBase<Long, AssetTypeRow, AssetTypeService> {
// ... contorller code
}
I do not have controller methods that mentions parameters with Spring's PathVariable annotation, and the point is I'm not allowed to do so (it's due to the fact that I'm building micro-framework).
So question is: how to teach swagger to discover path variables described using custom annotation HasCommonPathVariable applied at the controller level?

Ok, I've figured it out. Here is the solution. This bean needs to be registered in the context. Swagger will discover this bean and use it as one of the plugins to enrich operations
import java.util.ArrayList;
import java.util.List;
import org.apache.log4j.Logger;
import org.springframework.core.annotation.Order;
import com.fasterxml.classmate.TypeResolver;
import com.google.common.base.Optional;
import springfox.documentation.builders.ParameterBuilder;
import springfox.documentation.schema.ModelRef;
import springfox.documentation.service.Parameter;
import springfox.documentation.spi.DocumentationType;
import springfox.documentation.spi.service.OperationBuilderPlugin;
import springfox.documentation.spi.service.contexts.OperationContext;
import springfox.documentation.swagger.common.SwaggerPluginSupport;
#Order(SwaggerPluginSupport.SWAGGER_PLUGIN_ORDER + 1000)
public class CommonPathVariableOperationBuilderPlugin implements OperationBuilderPlugin {
protected Logger log = Logger.getLogger(getClass());
private TypeResolver typeResolver;
public CommonPathVariableOperationBuilderPlugin(TypeResolver typeResolver) {
this.typeResolver = typeResolver;
}
#Override
public boolean supports(DocumentationType delimiter) {
return true;
}
#Override
public void apply(OperationContext opCtx) {
List<Parameter> ret = new ArrayList<Parameter>();
Optional<HasCommonPathVariable> annSingle = opCtx.findControllerAnnotation(HasCommonPathVariable.class);
if (annSingle.isPresent()) {
ret.add(addParameter(annSingle.get()));
}
Optional<HasCommonPathVariables> annPlural = opCtx.findControllerAnnotation(HasCommonPathVariables.class);
if (annPlural.isPresent()) {
for (HasCommonPathVariable ann : annPlural.get().value()) {
ret.add(addParameter(ann));
}
}
opCtx.operationBuilder().parameters(ret);
}
private Parameter addParameter(HasCommonPathVariable ann) {
ParameterBuilder pb = new ParameterBuilder();
pb.parameterType("path").name(ann.name()).type(typeResolver.resolve(ann.type()));
pb.modelRef(new ModelRef("string"));
pb.required(true);
if (!"".equals(ann.defaultValue())) {
pb.defaultValue(ann.defaultValue());
}
return pb.build();
}
}

Bean cannot be autowired in a class

I'm using JWT (Json Web Token) to secure my Spring boot application.
There's a class which doesn't accept any bean.
First, I thought maybe the bean I want to inject is not defined. So I decided to print the list of beans names using spring ApplicationContext. But I found out that even ApplicationContext can not be injected into this class:
Any idea why this happens ?
import com.fasterxml.jackson.databind.ObjectMapper;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.context.ApplicationContext;
import org.springframework.security.authentication.AuthenticationManager;
import org.springframework.security.authentication.UsernamePasswordAuthenticationToken;
import org.springframework.security.core.Authentication;
import org.springframework.security.core.AuthenticationException;
import org.springframework.security.web.authentication.AbstractAuthenticationProcessingFilter;
import org.springframework.security.web.util.matcher.AntPathRequestMatcher;
import javax.servlet.FilterChain;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;
import java.util.Arrays;
public class JWTLoginFilter extends AbstractAuthenticationProcessingFilter {
#Autowired
private TokenAuthenticationService tokenAuthenticationService;
#Autowired
private ApplicationContext applicationContext;
public JWTLoginFilter(String url, AuthenticationManager authManager) {
super(new AntPathRequestMatcher(url));
setAuthenticationManager(authManager);
}
#Override
public Authentication attemptAuthentication(HttpServletRequest req,
HttpServletResponse res) throws AuthenticationException,
IOException, ServletException {
CustomUserDetails creds = new ObjectMapper().readValue(
req.getInputStream(), CustomUserDetails.class);
return getAuthenticationManager().authenticate(
new UsernamePasswordAuthenticationToken(creds.getUsername(),
creds.getPassword()));
}
#Override
protected void successfulAuthentication(HttpServletRequest req,
HttpServletResponse res, FilterChain chain, Authentication auth) {
java.util.List s = Arrays.asList(applicationContext.getBeanDefinitionNames());
System.out.println(s);
tokenAuthenticationService.addAuthentication(res, auth.getName());
}
}

The JWTLoginFilter has to be a bean as well to allow Spring to inject other beans into. Currently, Spring doesn't have any control over this. Marking the class with the #Component / #Service / #Repository annotations (depends on what role your filter plays, I assume the #Component is a good choice) is going to resolve the issue.
EDIT 1:
JWTLoginFilter required a bean of type java.lang.String that could not be found. Can a component have a constructor?
The problem: Spring tried to use a two-argument constructor to create a bean and was expected that these two arguments are its beans. But it's not true because there is no bean with the String class.
The solution: You should define a non-argument constructor to allow Spring to make an untuned instance without issues. Then create setters to provide methods which Spring will use to inject needed dependencies.
EDIT 2:
The workaround is to define a String bean (in a #Configuration class) which will be injected into the JWTLoginFilter constructor, but I'm not sure that your filter needs to have some external dependencies.
#Bean
public String getStringPatternBean() {
return "pattern";
}

Well, I finally decided to change how these classes are designed. I made methods inside TokenAuthenticationService static.

Hibernate Custom Annotation for Local Variables

I'm trying to create a custom annotation for local variables that pretty much do the same thing as #NotNull #NotEmpty and #NotBlank. I can't use those annotations since they don't apply for local variables so I decided to make my own annotation. Here's the annotation:
import controllers.validation.validator.NotNullOrEmptyValidator;
import javax.validation.Constraint;
import javax.validation.Payload;
import javax.validation.ReportAsSingleViolation;
import javax.validation.constraints.NotNull;
import javax.validation.constraints.Size;
import java.lang.annotation.*;
import static java.lang.annotation.ElementType.ANNOTATION_TYPE;
import static java.lang.annotation.ElementType.FIELD;
import static java.lang.annotation.ElementType.LOCAL_VARIABLE;
#Target(LOCAL_VARIABLE)
#Retention(RetentionPolicy.RUNTIME)
#Documented
#Constraint(validatedBy = NotNullOrEmptyValidator.class)
#ReportAsSingleViolation
public #interface NotNullOrEmpty {
String message() default "something is wrong!";
Class<?>[] groups() default {};
Class<? extends Payload>[] payload() default {};
#Target(LOCAL_VARIABLE)
#Retention(RetentionPolicy.RUNTIME)
#Documented
#interface List {
NotNullOrEmpty[] value();
}
}
And here's the validator:
import controllers.validation.constraints.NotNullOrEmpty;
import javax.validation.ConstraintValidator;
import javax.validation.ConstraintValidatorContext;
public class NotNullOrEmptyValidator implements ConstraintValidator<NotNullOrEmpty, Object> {
#Override
public void initialize(NotNullOrEmpty constraintAnnotation) {
}
#Override
public boolean isValid(Object value, ConstraintValidatorContext context) {
return value!=null && !value.toString().isEmpty();
}
}
But for some reason when I try to use it like this:
public class Foo {
public void doSomething(HttpServletRequest request) {
#NotNullOrEmpty(message = "headerpiece cannot be empty or null.")
String headerPiece = request.get("something");
}
}
It just doesn't fire. I've tried passing in that something value in the header with an empty string and tried not passing it in at all but the annotation just doesn't fire and neither does the validator. What am I doing wrong here?

Make sure it is deployed as a webapp. In my case it is not firing for test cases but gets fired in actual web application.

Use #Validated and #Valid with spring validator

I have a java bean being used to send JSON messages to a spring #RestController and I have bean validation setup and running just fine using #Valid. But I want to move to Protobuf/Thrift and move away from REST. It is an internal API and a lot of big companies have done away with REST internally. What this really means is that I no longer have control of the message objects - they are generated externally. I can't put annotations on them anymore.
So now my validation has to be programmatic. How do I do this? I have coded up a Validator and it works just great. But it doesn't use the nice #Valid annotation. I have to do the following:
#Service
public StuffEndpoint implements StuffThriftDef.Iface {
#Autowired
private MyValidator myValidator;
public void things(MyMessage msg) throws BindException {
BindingResult errors = new BeanPropertyBindingResult(msg, msg.getClass().getName());
errors = myValidator.validate(msg);
if (errors.hasErrors()) {
throw new BindException(errors);
} else {
doRealWork();
}
}
}
This stinks. I have to do this in every single method. Now, I can put a lot of that into one method that throws BindException and that makes it one line of code to add to every method. But that's still not great.
What I want is to see it look like this:
#Service
#Validated
public StuffEndpoint implements StuffThriftDef.Iface {
public void things(#Valid MyMessage msg) {
doRealWork();
}
}
And still get the same result. Remember, my bean has no annotations. And yes, I know I can use the #InitBinder annotation on a method. But that only works for web requests.
I don't mind injecting the correct Validator into this class, but I would prefer if my ValidatorFactory could pull the correct one based on the supports() method.
Is this possible? Is there a way to configure bean validation to actually use Spring validation instead? Do I have to hijack a Aspect somewhere? Hack into the LocalValidatorFactory or the MethodValidationPostProcessor?
Thanks.

Its pretty complicated thing to combine Spring validation and JSR-303 constrains. And there is no 'ready to use' way. The main inconvenience is that Spring validation uses BindingResult, and JSR-303 uses ConstraintValidatorContext as result of validation.
You can try to make your own validation engine, using Spring AOP. Let's consider, what we need to do for it. First of all, declare AOP dependencies (if you didn't yet):
<dependency>
<groupId>org.springframework</groupId>
<artifactId>spring-aop</artifactId>
<version>4.2.4.RELEASE</version>
</dependency>
<dependency>
<groupId>org.aspectj</groupId>
<artifactId>aspectjrt</artifactId>
<version>1.8.8</version>
<scope>runtime</scope>
</dependency>
<dependency>
<groupId>org.aspectj</groupId>
<artifactId>aspectjweaver</artifactId>
<version>1.8.8</version>
</dependency>
I'm using Spring of version 4.2.4.RELEASE, but of cause you can use your own. AspectJ needed for use aspect annotation. Next step, we have to create simple validator registry:
public class CustomValidatorRegistry {
private List<Validator> validatorList = new ArrayList<>();
public void addValidator(Validator validator){
validatorList.add(validator);
}
public List<Validator> getValidatorsForObject(Object o) {
List<Validator> result = new ArrayList<>();
for(Validator validator : validatorList){
if(validator.supports(o.getClass())){
result.add(validator);
}
}
return result;
}
}
As you see it is very simple class, which allow us to find validator for object. Now lets create annotation, that will be mark methods, that need to be validated:
package com.mydomain.validation;
#Target({ElementType.METHOD})
#Retention(RetentionPolicy.RUNTIME)
public #interface CustomValidation {
}
Because of standard BindingException class is not RuntimeException, we can't use it in overriden methods. This means we need define our own exception:
public class CustomValidatorException extends RuntimeException {
private BindingResult bindingResult;
public CustomValidatorException(BindingResult bindingResult){
this.bindingResult = bindingResult;
}
public BindingResult getBindingResult() {
return bindingResult;
}
}
Now we are ready to create an aspect that will do most of the work. Aspect will execute before methods, which marked with CustomValidation annotation:
#Aspect
#Component
public class CustomValidatingAspect {
#Autowired
private CustomValidatorRegistry registry; //aspect will use our validator registry
#Before(value = "execution(public * *(..)) && annotation(com.mydomain.validation.CustomValidation)")
public void doBefore(JoinPoint point){
Annotation[][] paramAnnotations =
((MethodSignature)point.getSignature()).getMethod().getParameterAnnotations();
for(int i=0; i<paramAnnotations.length; i++){
for(Annotation annotation : paramAnnotations[i]){
//checking for standard org.springframework.validation.annotation.Validated
if(annotation.annotationType() == Validated.class){
Object arg = point.getArgs()[i];
if(arg==null) continue;
validate(arg);
}
}
}
}
private void validate(Object arg) {
List<Validator> validatorList = registry.getValidatorsForObject(arg);
for(Validator validator : validatorList){
BindingResult errors = new BeanPropertyBindingResult(arg, arg.getClass().getSimpleName());
validator.validate(arg, errors);
if(errors.hasErrors()){
throw new CustomValidatorException(errors);
}
}
}
}
execution(public * *(..)) && #annotation(com.springapp.mvc.validators.CustomValidation) means, that this aspect will applied to any public methods of beans, which marked with #CustomValidation annotation. Also note, that to mark validated parameters we are using standard org.springframework.validation.annotation.Validated annotation. But of cause we could make our custom. I think other code of aspect is very simple and does not need any comments. Further code of example validator:
public class PersonValidator implements Validator {
#Override
public boolean supports(Class<?> aClass) {
return aClass==Person.class;
}
#Override
public void validate(Object o, Errors errors) {
Person person = (Person)o;
if(person.getAge()<=0){
errors.rejectValue("age", "Age is too small");
}
}
}
Now we have make tune the configuration and all ready to use:
#Configuration
#ComponentScan(basePackages = "com.mydomain")
#EnableAspectJAutoProxy(proxyTargetClass = true)
public class AppConfig{
.....
#Bean
public CustomValidatorRegistry validatorRegistry(){
CustomValidatorRegistry registry = new CustomValidatorRegistry();
registry.addValidator(new PersonValidator());
return registry;
}
}
Note, proxyTargetClass is true because we will use cglib class proxy.
Example of target method in service class:
#Service
public class PersonService{
#CustomValidation
public void savePerson(#Validated Person person){
....
}
}
Because of #CustomValidation annotation aspect will be applied, and because of #Validated annotation person will be validated. And example of usage of service in controller(or any other class):
#Controller
public class PersonConroller{
#Autowired
private PersonService service;
public String savePerson(#ModelAttribute Person person, ModelMap model){
try{
service.savePerson(person);
}catch(CustomValidatorException e){
model.addAttribute("errors", e.getBindingResult());
return "viewname";
}
return "viewname";
}
}
Keep in mind, that if you will invoke #CustomValidation from methods of PersonService class, validation will not work. Because it will invoke methods of original class, but not proxy. This means, that you can invoke this methods only from outside of class (from other classes), if you want validation to be working (eg #Transactional works same way).
Sorry for long post. My answer is not about 'simple declarative way', and possible you will do not need it. But I was curious resolve this problem.

I marked #Ken's answer as correct because it is. But I have taken it a little further and wanted to post what I have made. I hope anybody coming to this page will find it interesting. I might try to get it in front of the Spring folks to see if it might be something included in future releases.
The idea is to have a new annotation to replace #Valid. So I called it #SpringValid. Using this annotation would kick off the system put together above. Here are all the pieces:
SpringValid.java
package org.springframework.validation.annotation;
import static java.lang.annotation.ElementType.CONSTRUCTOR;
import static java.lang.annotation.ElementType.FIELD;
import static java.lang.annotation.ElementType.METHOD;
import static java.lang.annotation.ElementType.PARAMETER;
import static java.lang.annotation.RetentionPolicy.RUNTIME;
import java.lang.annotation.Retention;
import java.lang.annotation.Target;
#Target({METHOD, FIELD, CONSTRUCTOR, PARAMETER})
#Retention(RUNTIME)
public #interface SpringValid {
}
SpringValidationAspect.java
package org.springframework.validation;
import org.aspectj.lang.annotation.Aspect;
import org.aspectj.lang.annotation.Before;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Component;
import java.util.List;
#Aspect
#Component
public class SpringValidationAspect {
private SpringValidatorRegistry springValidatorRegistry;
#Autowired
public SpringValidationAspect(final SpringValidatorRegistry springValidatorRegistry) {
this.springValidatorRegistry = springValidatorRegistry;
}
public SpringValidatorRegistry getSpringValidatorRegistry() {
return springValidatorRegistry;
}
#Before("#target(org.springframework.validation.annotation.Validated) "
+ "&& execution(public * *(#org.springframework.validation.annotation.SpringValid (*), ..)) "
+ "&& args(validationTarget)")
public void beforeMethodThatNeedsValidation(Object validationTarget) {
validate(validationTarget);
}
private void validate(Object arg) {
List<Validator> validatorList = springValidatorRegistry.getValidatorsForObject(arg);
for (Validator validator : validatorList) {
BindingResult errors = new BeanPropertyBindingResult(arg, arg.getClass().getSimpleName());
validator.validate(arg, errors);
if (errors.hasErrors()) {
throw new SpringValidationException(errors);
}
}
}
}
Spring's examples show classes annotated with #Validated so I wanted to keep that. The above aspect only targets classes with #Validated at the class-level. And, just like when you use #Valid, it looks for the #SpringValid annotation stuck to a method parameter.
SpringValidationException.java
package org.springframework.validation;
import org.springframework.validation.BindingResult;
public class SpringValidationException extends RuntimeException {
private static final long serialVersionUID = 1L;
private BindingResult bindingResult;
public SpringValidationException(final BindingResult bindingResult) {
this.bindingResult = bindingResult;
}
public BindingResult getBindingResult() {
return bindingResult;
}
}
SpringValidatorRegistry.java
package org.springframework.validation;
import org.springframework.validation.Validator;
import java.util.ArrayList;
import java.util.List;
public class SpringValidatorRegistry {
private List<Validator> validatorList = new ArrayList<>();
public void addValidator(Validator validator) {
validatorList.add(validator);
}
public List<Validator> getValidatorsForObject(Object o) {
List<Validator> result = new ArrayList<>();
for (Validator validator : validatorList) {
if (validator.supports(o.getClass())) {
result.add(validator);
}
}
return result;
}
}
Just like the first answer, a place to register all classes that implement Spring's org.springframework.validation.Validator interface.
SpringValidator.java
package org.springframework.validation.annotation;
import org.springframework.stereotype.Component;
import java.lang.annotation.Documented;
import java.lang.annotation.ElementType;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;
#Target(ElementType.TYPE)
#Retention(RetentionPolicy.RUNTIME)
#Documented
#Component
public #interface SpringValidator {
}
This is just extra sauce to make it easier to register/find Validators. You could register all your Validators by hand, or you could find them via reflection. So this part is not required, I just thought it made things easier.
MyConfig.java
package com.example.config;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.context.ApplicationContext;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
import org.springframework.validation.SpringValidationAspect;
import org.springframework.validation.SpringValidatorRegistry;
import org.springframework.validation.annotation.SpringValidator;
import java.util.Map;
import javax.validation.Validator;
#Configuration
public class MyConfig {
#Autowired
private ApplicationContext applicationContext;
#Bean
public SpringValidatorRegistry validatorRegistry() {
SpringValidatorRegistry registry = new SpringValidatorRegistry();
Map<String, Object> validators =
applicationContext.getBeansWithAnnotation(SpringValidator.class);
validators.values()
.forEach(v -> registry.addValidator((org.springframework.validation.Validator) v));
return registry;
}
#Bean
public SpringValidationAspect springValidationAspect() {
return new SpringValidationAspect(validatorRegistry());
}
}
See, scan your classpath and look for #SpringValidator classes and register them. Then register the Aspect and away you go.
Here is an example of such a Validator:
MyMessageValidator.java
package com.example.validators;
import com.example.messages.MyMessage;
import org.springframework.validation.Errors;
import org.springframework.validation.ValidationUtils;
import org.springframework.validation.Validator;
import org.springframework.validation.annotation.SpringValidator;
#SpringValidator
public class MyMessageValidator implements Validator {
#Override
public boolean supports(Class<?> clazz) {
return MyMessage.class.isAssignableFrom(clazz);
}
#Override
public void validate(Object target, Errors errors) {
ValidationUtils.rejectIfEmpty(errors, "firstField", "{javax.validation.constraints.NotNull}",
"firstField cannot be null");
MyMessage obj = (MyMessage) target;
if (obj.getSecondField != null && obj.getSecondField > 100) {
errors.rejectField(errors, "secondField", "{javax.validation.constraints.Max}", "secondField is too big");
}
}
}
And here is the service class that uses the #SpringValid annotation:
MyService.java
package com.example.services;
import com.example.messages.MyMessage;
import org.springframework.validation.annotation.SpringValid;
import org.springframework.validation.annotation.Validated;
import javax.inject.Inject;
#Validated
public class MyService {
public String doIt(#SpringValid final MyMessage msg) {
return "we did it!";
}
}
Hope this makes sense for someone at some point. I personally think it is quite useful. A lot of companies are starting to move their internal APIs away from REST and to something like Protobuf or Thrift. You can still use Bean Validation but you have to use XML, and it isn't all that nice. So I hope this will be helpful to people who want to still do programmatic validation.

Hope it helps someone. I've got it working by adding the following configuration:
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
import org.springframework.validation.beanvalidation.LocalValidatorFactoryBean;
import org.springframework.validation.beanvalidation.MethodValidationPostProcessor;
#Configuration
public class ValidatorConfiguration {
#Bean
public MethodValidationPostProcessor getMethodValidationPostProcessor(){
MethodValidationPostProcessor processor = new MethodValidationPostProcessor();
processor.setValidator(this.validator());
return processor;
}
#Bean
public LocalValidatorFactoryBean validator(){
return new LocalValidatorFactoryBean();
}
}
The service is then annotated the same way (#Validated on the class and #Valid on the parameter) and can be injected into another bean where the method can be called directly and validation happens.