URLResource.isDirectory() throws a NullPointerException when created from a jar:file: URL

[wilkinsona]

Jetty version(s)
12.0.0.Beta2

Java version/vendor (use: java -version)

openjdk version "17.0.7" 2023-04-18 LTS
OpenJDK Runtime Environment (build 17.0.7+7-LTS)
OpenJDK 64-Bit Server VM (build 17.0.7+7-LTS, mixed mode, sharing)

OS type/version
macOS 13.4

Description
URI.getPath() can return null but URLResourceFactory.URLResource.isDirectory() assumes that it will not. This can result in a NullPointerException.

How to reproduce?

new URLResourceFactory().newResource(new URL("jar:file:/example.jar!/")).isDirectory();

[lorban]

You're right that this NullPointerException should not happen, so I've created a PR to fix this: #9985

But this looks like you're abusing the URLResourceFactory as it wasn't designed to handle file nor jar:file: URIs. Its only intended purpose is to be able to register a ResourceFactory handling HTTP or HTTPS schemes like so:

ResourceFactory.registerResourceFactory("https", new URLResourceFactory());

Using it for any other purpose sounds like abuse and makes me wonder what you're trying to achieve that cannot be done with the official ResourceFactory mechanism.

[joakime]

@lorban see issue #9973 for origin of this use

[wilkinsona]

Thanks, both. Just to provide a summary of the background, as a (possibly intermediate) step I am trying to get things working with Jetty 12 as they did with Resource.newResource(String) in Jetty 11. Until we have FileSystem support in Spring Boot's fat jars, the goal is to use a URL with our custom Handler for jar:file: URLs as Jetty 11 allowed.

[lorban]

I don't think URLResourceFactory is advanced enough to usefully handle jar:file URLs, and making it this capable sounds overkill as it would basically require duplicating MountedPathResource and its integration with FileSystemPool.

What kind of magic is your custom URLStreamHandler doing? Maybe that could be achieved another way?

[wilkinsona]

What kind of magic is your custom URLStreamHandler doing? Maybe that could be achieved another way?

It's a cornerstone of Spring Boot's executable jar support. I don't think it can be achieved in another way as a custom Handler is essential for compatibility with existing code that uses jar: URLs.

[lorban]

I'd like to understand better Spring Boot's executable jar support to try to figure out an elegant solution.

Barring that, URLResourceFactory will have fairly limited support: it is slow, isDirectory makes a guess, and there is no way to list sub-resources. Hopefully, if you have to resort to using that ResourceFactory, it's enough for your needs.