Class.getResource() vs. ClassLoader.getResource(): What's the Difference and When Should I Use Which?

Delving into the Differences between Class.getResource() and ClassLoader.getResource()

The distinction between Class.getResource() and ClassLoader.getResource() lies in the interpretation of the resource name.

Relative vs. Absolute Resource Names

Class.getResource() accepts both "relative" and "absolute" resource names. When using a relative name, the resource is interpreted relative to the package of the class. On the other hand, ClassLoader.getResource() always assumes an absolute path.

To illustrate this:

foo.bar.Baz.class.getResource("xyz.txt"); // relative name
foo.bar.Baz.class.getClassLoader().getResource("foo/bar/xyz.txt"); // equivalent

Leading Slash

In the context of Class.getResource(), a resource name prefixed with a leading slash ("/") is considered absolute. This is to align with the expected behavior when dealing with real filesystems.

foo.bar.Baz.class.getResource("/data/xyz.txt"); // absolute name
foo.bar.Baz.class.getClassLoader().getResource("data/xyz.txt"); // also absolute

Caching:

As for your question regarding caching, you are correct in your observation. Directory listings are cached by the ClassLoader, but not by Class.getResource(). This can lead to scenarios where newly created files or directory changes may not be reflected immediately using Class.getResource() but would be visible via ClassLoader.getResource().

The API documentation for Class.getResource() confirms this behavior:

"This method delegates to this object's class loader. If this object was loaded by the bootstrap class loader, the method delegates to ClassLoader.getSystemResource(java.lang.String)."

Recommendation

In general, it's recommended to use ClassLoader.getResource() if you need to access resources that may not be located within the package of the class. However, if you're specifically working with resources relative to the class's package and desire immediate reflection of directory changes, you can use Class.getResource() while being mindful of its caching limitations.

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