Java - Registering custom URL protocol handlers

Question

I tried to register a custom URL handler for a classpath protocol, as described in another thread. Here is the code:

package com.mycompany;

import org.junit.Test;
import java.net.MalformedURLException;
import java.net.URL;
import com.mycompany.protocol.classpath.Handler;

public class ParserTest {
    @Test
    public void testParsing() throws MalformedURLException {      
        System.out.println(System.getProperty("java.protocol.handler.pkgs"));

        //URL url = new URL(null, "classpath://com.mycompany/hello-world.xml", new Handler(ClassLoader.getSystemClassLoader()));
        URL url = new URL("classpath://com.mycompany/hello-world.xml");
    }
}

The test case has the following JVM arguments:

-Djava.protocol.handler.pkgs=com.mycompany.protocol

The System.out.println line properly outputs com.mycompany.protocol, so the property is being set. However, it looks like it's not being taken into effect, because the above call will throw a java.net.MalformedURLException: unknown protocol: classpath exception.

If I provide the handler explicitly as in the commented line, everything is fine. However, I would rather not provide it explicitly - it should be done automatically.

What am I doing wrong?

Answer 1

I have found the issue. The original classpath handler class that I used had a non-default constructor. Of course, because it had only a non-default constructor, the handler couldn't be instantiated. I apologize to everyone who have tried to debug this issue, I failed to see this connection.