Question

I wonder what the difference is between Class.getResource() and ClassLoader.getResource()?

edit: I especially want to know if any caching is involved on file/directory level. As in “are directory listings cached in the Class version?”

AFAIK the following should essentially do the same, but they are not:

getClass().getResource() 
getClass().getClassLoader().getResource()

I discovered this when fiddling with some report generation code that creates a new file in WEB-INF/classes/ from an existing file in that directory. When using the method from Class, I could find files that were there at deployment using getClass().getResource(), but when trying to fetch the newly created file, I recieved a null object. Browsing the directory clearly shows that the new file is there. The filenames were prepended with a forward slash as in “/myFile.txt”.

The ClassLoader version of getResource() on the other hand did find the generated file. From this experience it seems that there is some kind of caching of the directory listing going on. Am I right, and if so, where is this documented?

From the API docs on Class.getResource()

Finds a resource
with a given name. The rules for
searching resources associated with a
given class are implemented by the
defining class loader of the class.
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).

To me, this reads “Class.getResource is really calling its own classloader’s getResource()”. Which would be the same as doing getClass().getClassLoader().getResource(). But it is obviously not. Could someone please provide me with some illumination into this matter?

Answer 1

To answer the question whether there is any caching going on.

I investigated this point further by running a stand-alone Java application that continuously loaded a file from disk using the getResourceAsStream ClassLoader method. I was able to edit the file, and the changes were reflected immediately, i.e., the file was reloaded from disk without caching.

However:
I’m working on a project with several maven modules and web projects that have dependencies on each other. I’m using IntelliJ as my IDE to compile and run the web projects.

I noticed that the above seemed to no longer hold true, the reason being that the file that I was being loaded is now baked into a jar and deployed to the depending web project. I only noticed this after trying to change the file in my target folder, to no avail. This made it seem as though there was caching going on.