Mocking a URL in Java

Question

We have a URL object in one of our Java classes that we want to mock, but it\'s a final class so we cannot. We do not want to go a level above, and mock the InputStream beca

Answer 1

JMockit does indeed allow you to mock a final JRE class like java.net.URL.

It seems the Attach API in jdkDir/lib/tools.jar available in implementations of JDK 1.6 other than Sun's does not work as well. I guess this stuff is still too new/advanced, or simply didn't get the necessary attention from the other JDK vendors (Apple, IBM with the J9 JDK, Oracle with the JRockit JDK).

So, if you run into problems by having tools.jar in the classpath, try using the "-javaagent:jmockit.jar" JVM argument. It tells the JVM to directly load the java agent at startup, without using the Attach API. That should work in the Apple JDK 1.5/1.6.

Answer 2

I have used a URLHandler that allows me to load a URL from the classpath. So the following

new URL("resource:///foo").openStream()

would open a file named foo from within the class path. To do this, I use a common utility library and register a handler. To use this handler, you just need to call:

com.healthmarketscience.common.util.resource.Handler.init();

and the resource URL is now available.

Answer 3

When I have a class that can't be easily mocked because it is final (or sealed in C#), my usual route is to write a wrapper around the class and use the wrapper wherever I would use the actual class. Then I would mock out the wrapper class as necessary.

Answer 4

I went with the following:

public static URL getMockUrl(final String filename) throws IOException {
    final File file = new File("testdata/" + filename);
    assertTrue("Mock HTML File " + filename + " not found", file.exists());
    final URLConnection mockConnection = Mockito.mock(URLConnection.class);
    given(mockConnection.getInputStream()).willReturn(
            new FileInputStream(file));

    final URLStreamHandler handler = new URLStreamHandler() {

        @Override
        protected URLConnection openConnection(final URL arg0)
                throws IOException {
            return mockConnection;
        }
    };
    final URL url = new URL("http://foo.bar", "foo.bar", 80, "", handler);
    return url;
}

This gives me a real URL object that contains my mock data.