Obtaining a URL from a jimfs Path

[skuzzle]

A framework I'm testing internally needs to obtain an URL from a passed in path. For testing, I'd like to use jimfs, but obtaining a URL from a jimfs path seems not to be possible. Calling path.toUri().toURL() throws a MalformedURLException with message: java.net.MalformedURLException: unknown protocol: jimfs. Is this something fixable or something to live with? Here is a simpe test case to reproduce:

import java.net.MalformedURLException;
import java.net.URI;
import java.nio.file.FileSystem;
import java.nio.file.Path;

import org.junit.Test;

import com.google.common.jimfs.Configuration;
import com.google.common.jimfs.Jimfs;

public class JimFSTest {

    @Test
    public void testGetURL() throws MalformedURLException {
        final FileSystem fs = Jimfs.newFileSystem(Configuration.unix());
        final Path path = fs.getPath("foo", "bar");
        final URI uri = path.toUri();
        uri.toURL();
    }
}

Edit: I just found out that one can implement a URLStreamHandlerFactory to accomplish this. You might consider to ship a suitable implementation for jimfs.

[cgdecker]

It looks like for this to work there has to be a URLStreamHandler that handles the jimfs scheme. It doesn't seem like there's an especially great way to make that happen automatically.

Manually, you can create an implementation and then do:

URL url = new URL(null, path.toUri().toString(), new JimfsURLStreamHandler());

It's also possible to use URL.setURLStreamHandlerFactory(URLStreamHandlerFactory) to statically set a factory to use for getting URLStreamHandlers for custom protocols. Setting that would allow uri.toURL() to work, but it doesn't seem like a good idea for Jimfs to set the URLStreamHandlerFactory automatically because it would conflict with anything else that may also try to set the factory (that method can only be called once).

The final piece of complexity is just how the URLStreamHandler should behave. If you just want reading files by URL to work, it should be enough to create a URLConnection that only overrides getInputStream().

[seanrohead]

You don't need to change the default stream handler factory for this to work. If you have a Handler class in a sub-package named 'jimfs', then you can simply set the "java.protocol.handler.pkgs" system property to the parent package. It would be very helpful if the Handler class and a UrlConnection class shipped with jimfs. Here are the classes I use:

public class Handler extends URLStreamHandler
{
    @Override
    protected URLConnection openConnection(URL url) throws IOException
    {
        return new JimfsUrlConnection(url);
    }
}

public class JimfsUrlConnection extends URLConnection
{
    private Path path;

    public JimfsUrlConnection(URL url)
    {
        super(url);
    }

    @Override
    public void connect() throws IOException
    {
        try
        {
            FileSystem fileSystem = FileSystems.getFileSystem(URI.create("jimfs://" + getURL().getAuthority()));
            path = fileSystem.getPath(getURL().getPath());
        }
        catch (FileSystemNotFoundException | InvalidPathException e)
        {
            throw new IOException(e);
        }
    }

    @Override
    public InputStream getInputStream() throws IOException
    {
        Preconditions.checkState(path != null);

        return Files.newInputStream(path);
    }
}

[cgdecker]

This is in now, using the java.protocol.handler.pkgs approach. Thanks!