Re: FW: [jersey/jersey] SseEventSink invokes custom WriterInterceptor with wrong type, then throws NPE (#3592)

Pavel Bucek


yes, the issue is that mostly, you wouldn't want to mix "standard" response processing and SSE.

MessageBodyWriter is slightly different, since there is a type, the ultimate definition of that provider, which can be used for lookup and the registered provider won't have any consequence on running app, unless used as a return type. WriterInterceptor doesn't have anything like that - how would you mark the provider as "please use it only with some particular EventSink"? Also, if we'd think about symmetry - that would mean that we need to invoke ReaderInterceptor per each received client event.

EventSink is not a resource method, we have almost no control of the context from which it is invoked from. Allowing MessageBodyWriters to be invoked is a simplest enhancement compared to "writing only strings". Server sent event is supposed to be lightweight and cheap to send - notice that it doesn't need to be used, writing a string is still supported.

And your usecase - WriterInterceptor is not what you want to use in described scenario. You can implement a MessageBodyWriter, unwrap, lookup the MBW for the type you've unwrapped using injected Providers instance.


On 26/06/2017 21:45, Markus KARG wrote:



I know this is really late to discuss, but in fact, I doubt that it was a good decision to take WriterInterceptor out of the processing chain for SSE events.


In fact, today I set up a demo app and needed this, so I actually thought that this is a Jersey bug…!


Is there any good technical reason that made us strip WriterInterceptor from the processing chain (see below commit)?


Scenario where this is a problem: I wanted to add support for Optional<T> to demonstrate Java 8 support of JAX-RS. So I set up a WriterInterceptor which simply unwraps Optional to produce T, so all existing pre-2.1 EntityWriters for T will still work. Great. But fails with SSE! Hence, one must rewrite all WriterIntercepors if support for Optional<T> is needed with SSE. Very bad thing!


Why don't we use WriterInterceptors with SSE events?





From: Pavel Bucek [mailto:notifications@...]
Sent: Montag, 26. Juni 2017 09:38
To: jersey/jersey
Cc: Markus KARG; Author
Subject: Re: [jersey/jersey] SseEventSink invokes custom WriterInterceptor with wrong type, then throws NPE (#3592)


Please see this: jax-rs/spec@b4b0d91

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