To specify a request matcher in Java use the org.mockserver.model.HttpRequest class which specifies the details of each HTTP response with a fluent API.

For example:

HttpRequest httpRequest =
        request()
                .withMethod("POST")
                .withPath("/login")
                .withBody("{username: 'foo', password: 'bar'}")
                .withQueryStringParameters(
                        new Parameter("returnUrl", "/account")
                )
                .withCookies(
                        new Cookie("sessionId", "2By8LOhBmaW5nZXJwcmludCIlMDAzMW")
                );