How can I "intercept" a method call for a test?

I have a class like so:

class A {

    public static void makeCall() {
        URL url = "www.google.com";
        InputStream result = url.openStream();
        //Do more stuff
    }
}

And I want to write a unit test for it. What I want to happen is sort of "intercept" the call to openStream() so that I can run the static method makeCall() and just return some sort of hard coded JSON back, instead of actually making the call. I haven't been able to figure out how to mock this up, or if it's even possible.

I am looking for the same behavior as Angular's $httpBackend, any ideas or suggestions?