Answers to: Loading classes from WEB-INF/lib

Comment by Reto Weiss on Reto Weiss's answer

Reto Weiss — Thu, 11 Jul 2019 02:53:04 -0400

If you want to discuss this scenario in depth we can do a Skype call or organize a short meeting

Comment by Reto Weiss on Reto Weiss's answer

Reto Weiss — Thu, 11 Jul 2019 02:51:21 -0400

What if the implementation is in one project (lets say 'customer') and the interface is in another one (lets say 'standard'). Then the 'customer' project depends on 'standard'. Now 'standard' could evaluate all projects that depend on it and read the di config file from them and install this info into Guice. Then 'standard' shoud be able to inject an implementation of the interface into itselft. Be aware: The you have to ensure that the implementation class needs to be loaded with the classlaoder from 'customer' and not with the class laoder from 'standard'. But this should be possible.

Comment by vagabond on Lars Tuchel's question

vagabond — Wed, 10 Jul 2019 08:27:44 -0400

This is an interesiting problem. Suppose we could have a way by some ClassLoader black magic, how do you plan to deal with situation that different IARs depend on different version of the interface JARs. How to load the correct impl of the correct version? Something like versioning using package name may create a mess, I guess.

Comment by Lars Tuchel on Reto Weiss's answer

Lars Tuchel — Wed, 10 Jul 2019 04:27:25 -0400

There's a config file, where we can specify which implementation to use on a given environment and then we use guice to configure the inferfaces/implementations

Comment by Reto Weiss on Reto Weiss's answer

Reto Weiss — Wed, 10 Jul 2019 02:37:11 -0400

Hi Lars

How have you planed to inject the implementation into the project then? Or how can the project get an instance of the implementation?

Comment by Lars Tuchel on Reto Weiss's answer

Lars Tuchel — Wed, 10 Jul 2019 02:12:32 -0400

Hi Reto

Ok, I see. Thank you, Reto.

Basically we have some external services for which we define the interfaces in our projects. Then we'd like other third-party developers (that might not use ivy) to implement these interfaces. The approach works with both the interfaces and the implementation in WEB-INF/lib, but we would have preferred to deliver our interfaces directly with our iars.

Answer by Reto Weiss

Reto Weiss — Tue, 09 Jul 2019 11:28:32 -0400

Hi Lars

This will not work because the class loader hierarchy is exactly the opposite. This means the projects class loader has the web application class loader as parent. E.g. the project can load classes from WEB-INF/lib but not vice versa.

Can you tell me the use case behing your question?

Regards

Reto Weiss, Axon.ivy Support