Check the accepted answer for a similar question
How to handle Pop-up in Selenium WebDriver using Java
You need to - getWindowHandles - & then iterate over them.
Here is the working solution in case you still haven't figured it out (this is for the HDFC example)...
String test_URL = "http://www.hdfcbank.com/";
String css_login = "img#loginsubmit";
String css_popup_continue = "img[alt='Continue']";
browser = new FirefoxDriver();
browser.navigate().to(test_URL);
List<WebElement> objLogin = browser.findElements(By.cssSelector(css_login));
if (objLogin.size() > 0) {
objLogin.get(0).click();
String parentWindowHandle = browser.getWindowHandle(); // save the current window handle.
WebDriver popup = null;
Iterator<String> windowIterator = browser.getWindowHandles().iterator();
while(windowIterator.hasNext()) {
String windowHandle = windowIterator.next();
popup = browser.switchTo().window(windowHandle);
if (popup.getTitle().contains("NetBanking")) {
List<WebElement> objPopupElement = popup.findElements(By.cssSelector(css_popup_continue));
if(objPopupElement.size() > 0){
System.out.println("Switched to Popup and found element...");
objPopupElement.get(0).click();
//Do any other operations...
break;
}
}
}
//always safe to switch back to parent window to avoid any null pointers, unless parent process got closed...
browser.switchTo().window(parentWindowHandle);
}
else {
System.out.println("Logon button not found...");
}