How to check if an alert exists using WebDriver?

public boolean isAlertPresent() 
{ 
    try 
    { 
        driver.switchTo().alert(); 
        return true; 
    }   // try 
    catch (NoAlertPresentException Ex) 
    { 
        return false; 
    }   // catch 
}   // isAlertPresent()

check the link here https://groups.google.com/forum/?fromgroups#!topic/webdriver/1GaSXFK76zY