Given a classpath resource, is there a way to get the java.io.File object that has/contains it?

Question

If I have a resource on a classpath, I can both load it as stream fine, and there is even a URL representation of it. Unfortunately some implementations of the Url do not implement lastModified correctly.

What I would like is to take a path to something in the classpath, and then resolve it to a file that it is in on disk - if it in a jar, then a File pointing to the jar is fine. I can then get the lastModified from the File object instead of the URL, which will be more helpful.

Answer 1

No. This can't be done generally because URL can represent resources which are not associated with a file. For example, it can be HTTP, FTP or JNDI etc.

You can check for protocol and create the File yourself if the protocol is file-based, like "file://path", "jar://path!...".

Answer 2

Roughly speaking:

    URL url = this.getClass().getResource(myResource);
    String fileName;
    if (url.getProtocol().equals("file")) {
        fileName = url.getFile();        
    } else if (url.getProtocol().equals("jar")) {
        JarURLConnection jarUrl = (JarURLConnection) url.openConnection();
        fileName = jarUrl.getJarFile().getName();            
    } else {
        throw new IllegalArgumentException("Not a file");
    }
    File file = new File(fileName);
    long lastModified = file.lastModified();

Should do what you want. You will need to catch IOException.