[2.0] Wrong modules in JAVAX_WEBSOCKET_API_RULE

[boris-petrov]

I believe this is a mistake. org.apache.tomcat.embed:tomcat-embed-websocket is not an API, that's the implementation in the embedded Tomcat. It should not be replaced with anything as then projects don't work - i.e. it must be removed from that list. I'm not sure about the line above - org.apache.tomcat:tomcat-websocket - perhaps it also is an implementation, I'm not sure.

The same applies for all rules that contain these two modules.

P.S. I now see a similar problem with org.apache.tomcat.embed:tomcat-embed-core too.

[jjohannes]

I see what you mean, but the idea is that the capability JAVAX_WEBSOCKET_API_RULE means: These are alternatives that include the API (they may include more). And that is the case: org.apache.tomcat.embed:tomcat-embed-websocket does not only contain an implementation, but also all the API classes (e.g. javax.websocket.server.ServerContainer).

The general idea is that with theses rules, you will not have duplicated classes on the classpath anymore. If two Jars have overlapping classes, they have a shared capability. And that is the case here.

[boris-petrov]

Thanks for the answer! I understand what you're saying but in that case, if one has org.apache.tomcat.embed:tomcat-embed-websocket on their classpath, anything other than select(CapabilityDefinition.JAVAX_WEBSOCKET_API_RULE, 'org.apache.tomcat.embed:tomcat-embed-websocket') would cause their projects to not work, right? I agree with the general idea that preventing duplicate classes is great but in cases like these I think it doesn't make sense - it's better to have duplicate classes than a non-working project.

On the other side you do have a way to remove that:

patch.module('org.apache.tomcat.embed:tomcat-embed-websocket') {
	removeCapability(CapabilityDefinition.JAVAX_SERVLET_API)
	removeCapability(CapabilityDefinition.JAVAX_WEBSOCKET_API_RULE)
}

So I would understand if you don't want to "fix" it. It is a problem in the artifact itself after all - I guess it should not include these classes but rather depend on some other dependency... but that's the way it is.

[boris-petrov]

Speaking of the devil! 😄 In the new Tomcat version (9.0.88) they've made org.apache.tomcat.embed:tomcat-embed-websocket depend on org.apache.tomcat:tomcat-websocket-api! Which is great but... there are now duplicate classes between the two too. No matter, I just wanted to mention that. :)

[kmaterka]

Broken or not, tomcat-embed-core is widely used, especially in Spring Boot applications. It took me some time to identify problem and find solution.

Maybe when both javax.servlet-api and tomcat-embed-core are in classpath then it should select tomcat?

BTW, the removeCapability workaround works, thanks @boris-petrov !
This is another workaround:

conflictResolution {
    select(CapabilityDefinition.JAVAX_SERVLET_API, 'org.apache.tomcat.embed:tomcat-embed-core')
}