Is it possible with JSR-303 bean validation to write a custom annotation that can talk to a back end service?
We accomplished this type of validation with the "old school" Spring validators. In that case, the validator was a Spring bean and could have other services injected into it. Then that validator is injected into the controller.
An example might be an annotation (perhaps #EmailExists) to verify if an email already exists. I can only do this with a SQL query using one of our services. I would prefer to "validate" this alongside the other annotations and check it as soon as possible and not have to explicity do it in a back end service.
NOTE: We are using iBatis/MyBatis so I can't use any JPA/Hibernate tricks :-)
thanks!
That's definitely possible. Spring provides dependency injection support also within constraint validators. So you can simply inject any required services in your custom validators like this:
public class EmailExistsValidator implements ConstraintValidator<EmailExists, String> {
#Inject
private EmailValidationService service;
#Override
public void initialize(EmailExists constraintAnnotation) {}
#Override
public boolean isValid(String value, ConstraintValidatorContext context) {
if (value == null) {
return true;
}
return service.exists(value);
}
}
Depending on your concrete scenario it might be a good idea to first check "cheap" constraints such as #NotNull and only if these constraints are valid check more expensive constraints such as #EmailExists.
You can do this with help of group sequences and a redefined default group sequence for your type.
Related
I am building a REST API using spring and hibernate. I have come across the issue where I want to create a user and want to know the best practice on how to validate that the user can be created.
My controller has the #Valid annotation on the User object that gets passed into the method, and this checks for valid structure, however there is no #Unique property that gets picked up by #Valid.
I am using the #Column(unique = true) but this throws an error at the persistence level and I feel like that is quite low level and makes it difficult to throw a custom UsernameAlreadyExistsException().
My question here is what is the best practice in terms of preforming this type of validation. I thought about creating a custom annotation but it seems quite messy especially because as the project grows I would need multiple validators for different fields and it also seems to be closley related to tying the service layer to the annotation which seems messy
In my opinion, using custom annotation is the best approach to do stuff like this, you can inject some bean in ConstraintValidator and perform validation. However you can try one of the below unusual approaches, maybe it will fit your requirements.
Spring AOP
Spring Handler Interceptor
JPA Event Listeners
It's just my opinion about this, in most cases I think I will create custom annotations to handle it.
A good practice would be to put validation both on the database (which we know nothing about, but it is not complicated really) and on the Spring's side.
As #kamil-w already said, a good is to write custom constraint validator, see here for an example.
Keep in mind that you can always pass parameters like to constraint annotation, and then access them in your ConstraintValidator, for example.:
#Entity
public class Member {
// ...
#UniqueField(fieldName = "login", context = Member.class)
private String login;
}
#Component
public class UniqueFieldValidator implements ConstraintValidator<UniqueField, Object> {
#PersistenceUnit
private EntityManagerFactory emf;
private Class validationContext;
private String fieldName;
#Override
public void initialize(UniqueField uniqueField) {
this.validationContext = uniqueField.validationContext();
this.fieldName = uniqueField.fieldName();
}
#Override
public boolean isValid(Object value, ConstraintValidatorContext cxt) {
// use value, this.validationContext, this.fieldName and entity manager to check uniqueness
}
}
I'm integrating spring web sockets capability into an existing spring mvc application, everything works as expected, except for enabling custom Spring Conversion on my inbound messages via #DestinationVariable.
Now I already have custom converters fully working for the http side, ex #RequestParam or #PathVariable but the same conversion on a websocket controller method throws a ConverterNotFoundException
Ex. I have a custom converter that converts String into Users
public class StringToUserConverter implements Converter<String,User>{
#Autowired UserDAO userDAO;
#Override
public User convert(String id) {
return userDAO.getUser(Integer.parseInt(id));
}
}
And this works exactly as expected in my http controllers, where I can pass in an id, and its automatically converted to the domain class
public String myControllerMethod(#RequestParam User user)
However the same does not work for my websocket controller for a parameter annotated with #DestinationVariable
#MessageMapping("/users/{user}")
#SendTo("/users/greetings")
public String send(#DestinationVariable User user) {
return "hello"
}
I stepped through the code and I can see that the DestinationVariableMethodArgumentResolver has the default conversion service which doesnt include my custom coverters
So how do I register custom converters, or a custom ConversionService so that it works for web sockets like it already does for http controllers
So now I'm running into the same issue with #Header annotation for JmsListener methods.
Same idea, #Header User user, throws the ConverterNotFound exception.
#JmsListener(destination = "testTopic")
public void testJmsListener(Message m, #Header User user)..
Here I was trying to pass the user id on the message header, and have spring convert it, but to no avail, only basic default conversions are supported, like strings or numbers.
I have stepped through quite a bit of initialization code in Spring here, and I can see that a new DefaultConversionService gets instantiated in many places, without any consideration for external configuration.
It looks like these modules are not nearly as mature as Spring MVC or the developers took a shortcut. But based on my inspection there is no way to easily configure custom converters.
Ok and here is the very hacky, not recommended, approach that did work. Its pretty convoluted and brittle, Im not going to use it, but just for illustration purposes here is what it took to register a custom converter for #Header jms mapping.
Here Im passing in a user_email on the jms message header, and wanted spring to automatically convert the id/email into the actual domain object User. I already had a working converter that does this well in mvc/http mode.
public class StringToUserConverter implements Converter<String,User>{
#Autowired
UserDAO userDAO;
public User convert(String email) {
return userDAO.getByEmail(email);
}
}
The above part is pretty standard and straight forward. Here comes the idiotically convoluted part. I stepped through the spring jms listener initialization code and found lowest spot where I could cut-in with my custom converter for jms #Header.
I created a service, that will #Autowire one of springs Jms beans, and then sets a custom conversion service on it using #PostConstruct. Even here some of the properties were private, so I had to use reflection to read them
#Service
public class JmsCustomeConverterSetter {
#Autowired
StringToUserConverter stringToUserConverter;
#Autowired
JmsListenerAnnotationBeanPostProcessor jmsPostProcessor;
#PostConstruct
public void attachCustomConverters() throws NoSuchFieldException, SecurityException, IllegalArgumentException, IllegalAccessException {
//create custom converter service that includes my custom converter
GenericConversionService converterService = new GenericConversionService();
converterService.addConverter(stringToUserConverter); //add custom converter, could add multiple here
DefaultConversionService.addDefaultConverters(converterService); //attach some default converters
//reflection to read the private field so i can use it later
Field field = jmsPostProcessor.getClass().getDeclaredField("beanFactory"); //NoSuchFieldException
field.setAccessible(true);
BeanFactory beanFactory = (BeanFactory) field.get(jmsPostProcessor); //IllegalAccessException
DefaultMessageHandlerMethodFactory f = new DefaultMessageHandlerMethodFactory();
f.setConversionService(converterService);
f.setBeanFactory(beanFactory); //set bean factory read using reflection
f.afterPropertiesSet();
jmsPostProcessor.setMessageHandlerMethodFactory(f);
}
}
Creating the DefaultMessageHandlerMethodFactory was based on code I saw in org.springframework.messaging.handler.annotation.support.MessageHandlerMethodFactory.
I would definitely not recommend using this in production. It is fairly brittle and unnecessarily complex.
Spring...sometimes it's a breath of fresh air... and sometimes it's convoluted-clap-trap
I am using hibernate validator within a spring boot application.
I want to create an annotation, which will be validating updateability of a field. Something like #Updatable(WHILE_NEW).
I have created custom hibernate validator according to hibernate docs.
public class UpdatableConstraintValidator implements ConstraintValidator<UpdatableConstraint, Object> {
Updatable updatableMode;
#Override
public void initialize(UpdatableConstraint updatableConstraint) {
this.updatableMode = updatableConstraint.value();
}
#Override
public boolean isValid(Object field, ConstraintValidatorContext cxt) {
...some logic...
return result;
}
}
My question is, if there is a way to find out whether the operation which is being validated is CREATE or UPDATE?
And if it is UPDATE, is there a way to find out the old value of validated field?
Don't know about Spring Boot but I can say for sure that you won't be able to do that inside the Hibernate Validator boundaries.
Hibernate Validator just sees the current state of a bean and has absolutely no idea of its lifecycle.
I would like to build a Spring application, where new components can be added easily and without much configuration. For example: You have different kinds of documents. These documents should be able to get exported into different fileformats.
To make this functionality easy to maintain, it should (basically) work the following way:
Someone programs the file format exporter
He/ She writes a component, which checks if the file format exporter is licensed (based on Spring Conditions). If the exporter is licensed a specialized Bean is injected in the application context.
The "whole rest" works dynamically based on the injected beans. Nothing needs to be touched in order to display it on the GUI, etc.
I pictured it the following way:
#Component
public class ExcelExporter implements Condition {
#PostConstruct
public void init() {
excelExporter();
}
#Bean
public Exporter excelExporter(){
Exporter exporter= new ExcelExporter();
return exporter;
}
#Override
public boolean matches(ConditionContext context, AnnotatedTypeMetadata metadata) {
return true;
}
}
In order to work with those exporters (display them, etc.) I need to get all of them. I tried this:
Map<String, Exporter> exporter =BeanFactoryUtils.beansOfTypeIncludingAncestors(appContext, Exporter.class, true, true);
Unfortunate this does not work (0 beans returned). I am fairly new to this, would anyone mind to tell me how this is properly done in Spring? Maybe there is a better solution for my problem than my approach?
You can get all instances of a given type of bean in a Map effortlessly, since it's a built in Spring feature.
Simply autowire your map, and all those beans will be injected, using as a key the ID of the bean.
#Autowired
Map<String,Exporter> exportersMap;
If you need something more sophisticated, such as a specific Map implementation or a custom key. Consider defining your custom ExporterMap, as follows
#Component
class ExporterMap implements Map{
#Autowired
private Set<Exporter> availableExporters;
//your stuff here, including init if required with #PostConstruct
}
I have a spring 3 controller with a validator for one of the methods. It insists on validating every object on the model. Would anyone be able to explain to me why it does this or if I'm doing something wrong?
According to the docs, 5.7.4.3 Configuring a JSR-303 Validator for use by Spring MVC (http://static.springsource.org/spring/docs/3.0.0.RC3/spring-framework-reference/html/ch05s07.html)
With JSR-303, a single javax.validation.Validator instance typically validates all model objects that declare validation constraints. To configure a JSR-303-backed Validator with Spring MVC, simply add a JSR-303 Provider, such as Hibernate Validator, to your classpath. Spring MVC will detect it and automatically enable JSR-303 support across all Controllers.
Example:
#Controller
public class WhaleController {
#Autowired
private Validator myValidator;
#Autowired
private WhaleService whaleService;
#InitBinder
protected void initBinder(WebDataBinder binder) {
binder.setValidator(this.myValidator);
}
#RequestMapping(value="/save-the-whales")
#Transactional
public void saveTheWhales(#Valid WhaleFormData formData, BindingResult errors, Model model) {
if (!errors.hasFieldErrors()) {
Whale whale = new Whale();
whale.setBreed( formData.getBreed() );
this.whaleService.saveWhale( whale );
model.addAttribute("whale", whale);
}
model.addAttribute("errors", errors.getFieldErrors());
}
}
When run it will complain that Whale is an invalid target for myValidator (which is set to validate WhaleFormData, and does so fine). Whale is a POJO with no validation constraints, annotation and no config anywhere. Through trial and error I've found that ANY object placed on the model will attempt to be validated and fail if the validator is not setup to handle it. Primitives are just fine.
Can anyone tell me why this is, point me to the appropriate documentation and/or tell me the best way to put something on the model without having it validated?
In the case above I would like to place "whale" on the model as it will now have a unique whaleId() that it received from my persistence layer.
Thanks!
I guess this behaviour is not covered in the documentation well.
The problem is caused by the following:
By default, #InitBinder-annotated method is called for each non-primitive model attribute, both incoming and outcoming (the purpose of calling it for outcoming attibutes is to allow you to register custom PropertyEditors, which are used by form tags when rendering a form).
DataBinder.setValidator() contains a defensive check that call Validator.supports() and throws an exception if false is returned. So, there is no attempt to perform a validation, just an early check.
The solution is to restrict the scope of #InitBinder to particular attribute:
#InitBinder("whaleFormData")
protected void initBinder(WebDataBinder binder) { ... }