Make RedisOperationsSessionRepository.RedisSession public

[vijayaggarwal]

I use spring-session in a non-HTTP setup. I grab an instance of RedisOperationsSessionRepository and use it to create and save sessions. However, RedisOperationsSessionRepository creates sessions to type RedisSession, which is non-Public. This severely limits my ability to work with RedisSessions.

@Autowired
RedisOperationsSessionRepository sessionRepo;

Session session = sessionRepo.createSession();
session.setAttribute("key", "value");
sessionRepo.save(session); // Compiler error: save() expects argument of type RedisSession

RedisSession redisSession = (RedisSession) session; // Compiler error: RedisSession is not visible here
sessionRepo.save(session);

PS: I found #114 and #725 to be somewhat related to this one, so mentioning them here.

[vpavic]

@vijayaggarwal You should code against Spring Session's public APIs, rather than implementation. Here's an some examples:

Raw type approach:

class RawConsumer {

	@Autowired
	private FindByIndexNameSessionRepository sessionRepository;

	void consume() {
		Session session = (Session) this.sessionRepository
				.findByIndexNameAndIndexValue(FindByIndexNameSessionRepository.PRINCIPAL_NAME_INDEX_NAME, "principal")
				.values().iterator().next();
		session.setAttribute("test", UUID.randomUUID().toString());
		this.sessionRepository.save(session);
	}

}

Parameterized type approach:

class ParameterizedConsumer<S extends Session> {

	@Autowired
	private FindByIndexNameSessionRepository<S> sessionRepository;

	void consume() {
		S session = this.sessionRepository
				.findByIndexNameAndIndexValue(FindByIndexNameSessionRepository.PRINCIPAL_NAME_INDEX_NAME, "principal")
				.values().iterator().next();
		session.setAttribute("test", UUID.randomUUID().toString());
		this.sessionRepository.save(session);
	}

}

See also #849.

Closing as answered. If you have additional questions or feel that your original question isn't properly answered, please re-open the issue.

[vijayaggarwal]

Thanks for the reply @vpavic! Your example works as you are not calling SessionRepository#save (I guess servlet container calls that method in your case). However, since I am not using a servlet container, I need to call save myself. Reproducing my code sample:

@Autowired
SessionRepository<? extends Session> sessionRepo;

Session session = sessionRepo.createSession();
session.setAttribute("key", "value");
sessionRepo.save(session); // Compiler error

I can use raw type (i.e. SessionRepository instead of SessionRepository<? extends Session>), but that would be far from ideal.

[vijayaggarwal]

@vpavic Also, I cannot re-open this issue. Please consider re-opening it or suggest some other way forward. Thanks a lot!

[vpavic]

Sorry for confusion @vijayaggarwal, I've pasted the wrong example in my answer (though I've linked an issue that contained it) - I've updated the previous comment to address that.

[vijayaggarwal]

Thanks @vpavic! I will definitely prefer ParameterizedConsumer as it provides better type safety. However, to create an instance of ParameterizedConsumer, I need to specify a concrete type for its wildcard type parameter <? extends Session>.

If I try to create an instance of ParameterizedConsumer<Session>, autowiring of FindByIndexNameSessionRepository inside ParameterizedConsumer fails. I guess that's because the bean I am configuring is of type RedisOperationsSessionRepository which implements FindByIndexNameSessionRepository<RedisOperationsSessionRepository.RedisSession>, which is not compatible with FindByIndexNameSessionRepository<Session>, even if RedisSession implements Session, as generic types in Java are invariant.

So, I can't use your parameterized type approach as I can't create an instance of ParameterizedConsumer that successfully autowires my RedisOperationsSessionRepository. I can use the raw type approach, but I would not want to use it as it bypasses all type checking.

Also, if RedisOperationsSessionRepository is a public class, I think RedisSession should also be public, especially given that multiple methods of RedisOperationsSessionRepository accept/return RedisSession thereby "leaking" RedisSession in public API.

[vpavic]

However, to create an instance of ParameterizedConsumer, I need to specify a concrete type for its wildcard type parameter <? extends Session>.

That shouldn't be the case. We have quite a few SessionRepository consumers in our own codebase that use this pattern, e.g. SessionRepositoryFilter, SessionRepositoryMessageInterceptor, SpringSessionBackedSessionRegistry, SpringSessionBackedSessionInformation.

[vijayaggarwal]

That shouldn't be the case.

AKAIK, that's how Java works.

I looked through spring-session codebase as well. The classes you mentioned are themselves parameterized (e.g., SessionRepositoryFilter<S extends Session>, SessionRepositoryMessageInterceptor<S extends Session>) so the responsibility of specifying the concrete type is passed downstream. In a few places, I found the use of raw types with unchecked casts to bypass type checks, e.g.,

spring-session/spring-session-core/src/main/java/org/springframework/session/web/socket/config/annotation/AbstractSessionWebSocketMessageBrokerConfigurer.java

Lines 81 to 82 in 003996a

	@SuppressWarnings("rawtypes")
	private SessionRepository sessionRepository;

and

spring-session/spring-session-core/src/main/java/org/springframework/session/web/socket/config/annotation/AbstractSessionWebSocketMessageBrokerConfigurer.java

Lines 127 to 130 in 003996a

	@SuppressWarnings("unchecked")
	public SessionRepositoryMessageInterceptor<S> sessionRepositoryInterceptor() {
	return new SessionRepositoryMessageInterceptor<>(this.sessionRepository);
	}

Suppressing type checks works but isn't desirable. There should be a better way.

[vpavic]

The classes you mentioned are themselves parameterized (e.g., SessionRepositoryFilter<S extends Session>, SessionRepositoryMessageInterceptor<S extends Session>) so the responsibility of specifying the concrete type is passed downstream.

Exactly, that's the point, hence the ParameterizedConsumer example. What's exactly preventing you to register ParameterizedConsumer as a bean and have it inject the SessionRepository? We do the same ourselves, for example in SpringHttpSessionConfiguration:

spring-session/spring-session-core/src/main/java/org/springframework/session/config/annotation/web/http/SpringHttpSessionConfiguration.java

Lines 123 to 131 in 7fdf287

	@Bean
	public <S extends Session> SessionRepositoryFilter<? extends Session> springSessionRepositoryFilter(
	SessionRepository<S> sessionRepository) {
	SessionRepositoryFilter<S> sessionRepositoryFilter = new SessionRepositoryFilter<>(
	sessionRepository);
	sessionRepositoryFilter.setServletContext(this.servletContext);
	sessionRepositoryFilter.setHttpSessionIdResolver(this.httpSessionIdResolver);
	return sessionRepositoryFilter;
	}

[vijayaggarwal]

Ah, got it now! Registering as bean does the trick. If ParameterizedConsumer is a bean, I don't need to create it myself (as Spring creates it for me), and hence I don't need to provide a concrete type for its type parameter.

@Component
class MyController<S extends Session> {
    @Autowired
    SessionRepository<S> sessionRepo;

    public void myMethod() {
        S session = sessionRepo.createSession();
        session.setAttribute("key", "value");
        sessionRepo.save(session);
    }
}

I never specified what S is. I don't even need to. With this, I could also code against the generic SessionRepository class instead of coding against a particular implementation.

Closing the issue. Thanks a lot for help @vpavic!

[vijayaggarwal]

Btw, somewhat in relation to #114 also, if you think it helps to add a sample project on custom SessionRepository, I can submit a PR.

[vpavic]

Thanks for following up @vijayaggarwal, glad to hear you had this resolved.

Btw, somewhat in relation to #114 also, if you think it helps to add a sample project on custom SessionRepository, I can submit a PR.

Regarding this, please drop a note on #114 itself, since that issue is still open. Thanks!