RFE: Duplicate checker

I have used this library to implement a classpath duplicate checker. The gist of it is basically:

Map<String, List<String>> check() {
        Map<String, List<String>> seen = new HashMap<>();
        try (ScanResult scanResult = new ClassGraph().enableClassInfo().ignoreClassVisibility().scan()) {
            for (Resource resource : scanResult.getAllResources()) {
                String path = resource.getPath();
                @Var List<String> classpathElements = seen.get(path);
                if (classpathElements == null) {
                    classpathElements = new ArrayList<>(1);
                    seen.put(path, classpathElements);
                }
                classpathElements.add(getClasspathElementString(resource));
            }
        }
        return seen.entrySet().stream().filter(entry -> entry.getValue().size() > 1)
                .filter(entry -> !isHarmlessDuplicate(entry.getKey()))
                .collect(Collectors.toMap(Map.Entry::getKey, Map.Entry::getValue));
    }

Basically I re-built something very similar to https://github.com/jhades/ (see http://jhades.github.io) or https://github.com/basepom/duplicate-finder-maven-plugin but using classgraph. (The motivation for this was that JHades could not support Java 9+.)

Filing this issue here to ask whether a contribution (PR) of utility class like my ClasspathHellDuplicatesChecker into this lib would be of any interest. Alternative I could just add a link to it somewhere in the doc to make it easier and let people build something like it.

Also absolutely no offense taken if this doesn’t fit here - just close in that case, no worries.

[lukehutch]

Erm … but that’s perfectly fine, right? That’s kind of the point of what I’m after - to find duplicate classes in different JARs, when you (or an external 3rd-party) made a mess of your dependencies. You can’t really have a duplicate of the exact same class in the same single JAR.

Yes, it’s fine, I just wanted to make the distinction between multiple listings of the same jar on the classpath, and multiple occurrences of the same file within different classpath elements. The first cannot be detected (but may still be considered by somebody to be problematic), but the second can.

[vorburger]

if the exact same path or URL (after canonicalization) is listed on the classpath or module path multiple times, the second and subsequent are ignored by ClassGraph (since that is more of less semantically what the JRE does too). Therefore, duplicates are only detected if the same resources are present in multiple different modules, jars or directories.

Erm … but that’s perfectly fine, right? That’s kind of the point of what I’m after - to find duplicate classes in different JARs, when you (or an external 3rd-party) made a mess of your dependencies. You can’t really have a duplicate of the exact same class in the same single JAR.

Maintaining isHarmlessDuplicate() over the years is going to be a Herculean effort, good luck 😄

I’m not planning to… 😈

PS you should assign the ScanResult in a try-with-resources statement, so that proper cleanup does not depend upon a finalizer.

Thanks for noticing and pointing it out - fixed in https://git.opendaylight.org/gerrit/#/c/80158.