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note: this is a named-module java project

Why does getting a resources in java work like this? I got two packages, in main func both are printing the URL of "/respath/tmp.txt" in a jar-file syntax with corresponding to its classes.

How does this code really deffer to each other?

// mod-one
package com.pkg.one;
import ...
import com.pkg.two.ClassNameTwo;
class ClassNameOne {
    ... main()
        print(ClassNameOne.class.getResource("/resPath/tmp.txt")); // works fine
        print(ClassNameTwo.getCustomRes("resPath/tmp.txt", ClassNameOne.class); // it return null
}

note: this is a named-module java project

// mod-two
package com.pkg.two;
import ...
class ClassNameTwo {

    /**
     return "ClassLoader.getSystemResource(...)" if sourceClass is null.
     */
    public static URL getCustomRes(String sourcePath, Class<?> sourceClass) {
        ...
        URL url = null;
        if (sourceClass == null)
            url = ClassLoader.getSystemResource(sourcePath);
        else
            url = sourceClass.getResource("/" + sourcePath);    
        ...
        return url;
        }
}
Liveon Phoenix
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1 Answers1

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ok, I got an answer.Because this is a named-module java project you need to give access at to your "resouce-dir" to another module but why did it gives me a warning: "package is empty or does not exist", when it is not empty?

e.q:

module mod.one { // this module need to access the "res-dir" of mod.two
   requires mod.two;
   ...
}

module mod.two {
   ...
   opens my.path.to.res; // dir: my/path/to/res
}

And can we access/modify a third-party module res-dir that is not open?

Liveon Phoenix
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  • "_but why did it gives me a warning: "package is empty or does not exist", when it is not empty?_" – Are you using Maven or Gradle? If so, then the reason might be because technically the resources aren't in the module (at compile-time) due to the separation of `src/main/java` and `src/main/resources`. This is not really a problem, as everything ends up together when packaged. – Slaw Nov 11 '21 at 05:10
  • Also, note what you're dealing with is known as "encapsulation". It's described here: https://docs.oracle.com/en/java/javase/17/docs/api/java.base/java/lang/Module.html#getResourceAsStream(java.lang.String) – Slaw Nov 11 '21 at 05:14
  • Oh thank you very much for the info. yes I'm using a build-tool, is there a way to stop/fix the warning? – Liveon Phoenix Nov 11 '21 at 05:24
  • Which build tool are you using? – Slaw Nov 11 '21 at 05:29
  • @Slaw, um its Gradle build tool. – Liveon Phoenix Nov 11 '21 at 05:37
  • One of my answers to a different question provides some workarounds when using Gradle: https://stackoverflow.com/questions/51864473/where-do-resource-files-go-in-a-gradle-project-that-builds-a-java-9-module/51921521#51921521. But I do stand by what I said before in my now-deleted comment: Fixing this may be more effort than it's worth, especially if everything is working. – Slaw Nov 11 '21 at 05:41
  • Is the linked answer supposed to prevent that "package is empty or does not exist" warning? In a modular project which ONLY has a resource (no classes) in a package that is opened, I still see the warning using the new inferModulePath setting. I don't like telling people "just ignore the warning", ignoring warnings is a bad practice (we should at least actively suppress them and indicate that it was reviewed). We need some way to prevent that false positive warning, if only to avoid confusing other devs building your project with "warnings we should ignore". – Manius Feb 18 '23 at 21:27
  • Probably the simpliest workaround is to just move those resources to a package which also happens to have classes, or to add a dummy class in your src. Not the biggest issue in the world but still would be nice to allow for these "resource only packages" without our build tool whining at us for it. – Manius Feb 18 '23 at 21:42