I’m looking at a piece of Java code right now, and it takes a path as a String and gets its URL using
URL resource = ClassLoader.getSystemClassLoader().getResource(pathAsString);, then calls
String path = resource.getPath() and finally executes
Oh, and there are also calls to
URL url = resource.toURI(); and
String file = resource.getFile().
I’m totally confused right now – mostly because of the terminology, I guess. Can someone please walk me through the differences, or provide a few links to Dummy-proof material? Especially URI to URL and Resource to File? To me, it feels like they should be the same thing, respectively…
The difference between
getPath() is explained here: What’s the difference between url.getFile() and getpath()? (Interestingly they both seem to return Strings, which probably adds a whole lot to my state of mind…)
Now, if I have a locator that references a class or package in a jar file, will those two (i.e. path an file strings) differ?
resource.toString() would give you
jar:file:/C:/path/to/my.jar!/com/example/, after all (note the exclamation mark).
Is the difference between URI and URL in Java that the former doesn’t encode spaces? Cf. Files, URIs, and URLs conflicting in Java (This answer explains the general, conceptual difference between the two terms fairly well: URIs identify and URLs locate;)
Lastly – and most importantly – why do I need
File object; why isn’t a Resource (
URL) enough? (And is there a Resource object?)
Sorry if this question is a bit unorganized; it just reflects the confusion I have… 🙂
UPDATE 2017-04-12 Check JvR’s answer as it contains more exhaustive and exact explanation!
Please note that I do not consider myself 100% competent to answer, but nevertheless here are some comments:
Filerepresents a file or directory accessible via file system
resource is a generic term for a data object which can be loaded by the application
- usually resources are files distributed with the application / library and loaded via class-loading mechanism (when they reside on class-path)
URL#getPathis getter on the path part of URL (
URL#getFileas per JavaDoc returns
URI is just a data structure for manipulating the generic identifier itself.
URL on the other hand is really a resource locator and offers you features to actually read the resource via registered
URLs can lead to file-system resources and you can construct URL for every file system resource by using
file:// protocol (hence
Also be aware that that
URL#getFile is unrelated to
Why do I need File object; why isn’t a Resource (URL) enough?
It is enough. Only if you want to pass the resource to some component which can work only with files, you need to get
File from it. However not all resource URLs can be converted to
And is there a Resource object?
From the JRE point of view, it’s just a term. Some frameworks provide you with such class (e.g. Spring’s Resource).