Does Java getResource method only work with particular extensions?

The following piece of code works fine

getClass().getResource("/index.xml");

However when I do a full refactor to

getClass().getResourc开发者_StackOverflow社区e("/index.html");

The above line throws NullPointerException. I know I have refactored correctly because I rename the file using IDE smart refactor i.e. the file index.html definitely exists in the same directory. As soon as I switch back to

getClass().getResource("/index.xml");

Everything is fine again. Is there any reason why only the .xml extension works?

As @a_horse_with_no_name mentions, using getResourceAsStream( ) should work fine with any file and any extension.

I'd be inclined to believe (based on the information presented) that your IDE hasn't properly refreshed its file hierarchy after the refactor. I'd suggest running a full clean and build of your project, see if that helps the situation.

So, most of the other answers, the class/class loader shouldn't be looking at file extension You could write a ClassLoader which did that, but it would be odd.

I'm going to take a stab at what your problem is. I am guessing using some IDE (you don't specify which) that is copying certain files from your source folder into the destination (either a jar or a directory of classes and resources). For Java code, you want the compiled .class object files there and not the .java sources. So the IDE will be configured, with some reasonable default [magic], to copy files with only certain extensions. HTML files were used for old package JavaDocs (package-info.html rather than package-info.java which can include package-wide annotations), so are arguably reasonable to exclude by default.

Therefore, you should investigate what the project is doing in this area, and change any configurations accordingly.

Using getResourceAsStream() should work with any file extension (at least it does for me)

Recognised Java Resources are either a class extending ResourceBundle or .property file.

You can write your own extenstions to enable Resource to be gathered from other extensions.

I'm unsure why .xml files are a viable extension. Are you using Java 7?

From the JavaDoc guide:

The name of a resource is independent of the Java implementation; in particular, the path separator is always a slash (/). However, the Java implementation controls the details of how the contents of the resource are mapped into a file, database, or other object containing the actual resource.

A resource is identified by a string consisting of a sequence of substrings, delimited by slashes (/), followed by a resource name. Each substring must be a valid Java identifier. The resource name is of the form shortName or shortName.extension. Both shortName and extension must be Java identifiers.

And read this doc which tell us : an absolute resource name is constructed from the given resource name using this algorithm.

getResource() will work regardless of the type of resource. All it does it return a URL. This example works fine for me.

public class Example {
    public static void main(String... args) {
        System.out.println(Example.class.getResource("jaxb.properties"));
        System.out.println(Example.class.getResource("test.xml"));
        System.out.println(Example.class.getResource("foo.html"));
        System.out.println(Example.class.getResource("danger.exe"));
    }
}