Switch between two browser windows using Selenium WebDriver

you can use following code to switch between windows based on the window title

 private void handleMultipleWindows(String windowTitle) {
            Set<String> windows = driver.getWindowHandles();

            for (String window : windows) {
                driver.switchTo().window(window);
                if (driver.getTitle().contains(windowTitle)) {
                    return;
                }
            }
        }

Similary you could use URL or some other criteria to switch windows.