Working With Pop-ups In Selenium WebDriver:

This function will fetch message on Pop-up

public static String getPopupMessage(final WebDriver driver) {
String message = null;
try {
Alert alert = driver.switchTo().alert();
message = alert.getText();
alert.accept();
} catch (Exception e) {
message = null;
}
System.out.println("message"+message);
return message;
}

This function will Canceling pop-up in Selenium-WebDriver

public static String cancelPopupMessageBox(final WebDriver driver) {
String message = null;
try {
Alert alert = driver.switchTo().alert();
message = alert.getText();
alert.dismiss();
} catch (Exception e) {
message = null;
}
return message;
}