Loading resources from another module

Sander Mak sander.mak at luminis.eu
Sat Jan 21 19:18:35 UTC 2017

I have module A trying to read a resource in module B. The resource is in module B under 'pkg/resource.txt' and if I understood [1] correctly should be encapsulated by default. There are no opens/exports statements in module B's module-info. Module A tries to load 'pkg/resource.txt (after obtaining moduleB from the boot layer):


This returns null, which is expected behavior. Then, however, it tries to load the same resource with a slash in front of pkg:


Lo and behold, an InputStream is returned, giving module A access to module B's resource from an encapsulated package. In fact, you can prefix arbitrarily many slashes and it works. That can't be right, can it? The resource encapsulation shouldn't be optional depending on how Module::getResourceAsStream is called from another module, should it? I believe this is an issue in the handling of leading (or duplicate!) slashes in jdk.internal.loader.getPackageName and the subsequent jdk.internal.module.Checks::isPackageName that's called. This returns false for the invocation with "/pkg/resource.txt", which misleads Module::getResourceAsStream to get access. When you call it with "pgk//resource.txt" it will also happily provide the InputStream

[1] http://mail.openjdk.java.net/pipermail/jpms-spec-experts/2016-September/000392.html

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