How can I create a FileSystem to a jar inside another jar

Question

I am trying to use NIO FileSystem to access a jar inside another jar. Call the outside jar my-outer.jar and the inner my-inner.jar (Using Java 8 and Windows 7 but I think that is not the issue)

I am using the following code

    String zipfilePath = "c:/testfs/my-outer.jar!/my-inner.jar";
    Path path = Paths.get(zipfilePath);
    try(ZipFileSystem zipfs = (ZipFileSystem) FileSystems.newFileSystem(path, null))
    { ...  }

but I am getting the exception below when trying to create that newFileSystem:

Exception in thread "main" java.nio.file.FileSystemNotFoundException: C:\testfs\my-outer.jar!\my-inner.jar

Note that if I just use the outer jar as the FileSystem, that works perfectly fine and I can read and write files from it beautifully. It's just when I try to reach into the inner archive that the troubles begin.

Doesn't FileSystem support the JarURLConnection notation?

Answer 1

As said by vbezhenear and as experimented by myself the JarURLConnection notation in the form c:/testfs/my-outer.jar!/my-inner.jar seems not implemented by the factory method FileSystems.newFileSystem(Path path, ClassLoader loader).

But you can still access the inner jar like this:

Path outerPath = Paths.get("c:/testfs/my-outer.jar");
try (FileSystem outerFS = FileSystems.newFileSystem(outerPath, null)) {
    Path innerPath = outerFS.getPath("/my-inner.jar");
    try (FileSystem innerFS = FileSystems.newFileSystem(innerPath, null)) {
       ...
    }
}

--UPDATE--

If you try to use an URI instead of a Path you can create a ZipFileSystem like this

URI uri = URI.create("jar:file:/home/orto/stackoverflow/outer.jar!/inner.jar");
Map<String,String> env = Collections.emptyMap();
try(ZipFileSystem zipfs = (ZipFileSystem)FileSystems.newFileSystem(uri,env))
{...}

But no luck you get access to the outer.jar and not the inner.jar

If you look at the source code of JarFileSystemProvider you see

@Override
protected Path uriToPath(URI uri) {
    String scheme = uri.getScheme();
    if ((scheme == null) || !scheme.equalsIgnoreCase(getScheme())) {
        throw new IllegalArgumentException("URI scheme is not '" + getScheme() + "'");
    }
    try {
        String uristr = uri.toString();
        int end = uristr.indexOf("!/");
        uristr = uristr.substring(4, (end == -1) ? uristr.length() : end);
        uri = new URI(uristr);
        return Paths.get(new URI("file", uri.getHost(), uri.getPath(), null))
                    .toAbsolutePath();
    } catch (URISyntaxException e) {
        throw new AssertionError(e); //never thrown
    }
}

The path is cut up before the first "!". So there is no way to directly create a file system on the inside jar from the newFileSystem method.