Capture screenshot

How to take the screenshot of failed test case with test case name? For example: Suppose the test case name is testVelifyLogin(). If it fails then my screenshot name should be testVelifyLogin_time_date.jpg

Please help me how to do this.

i have written code for screen shot as following:

public void onTestFailure(ITestResult iTestResult) {

    String path = System.getProperty("user.dir") + "\\TestOutput\\ScreenShots";

    DateFormat dateFormat = new SimpleDateFormat("HH_mm_ss_dd_MM");
    Calendar cal = Calendar.getInstance();
    String date = dateFormat.format(cal.getTime());
     File scrFile = ((TakesScreenshot) driver)
            .getScreenshotAs(OutputType.FILE);

    try {
        FileUtils.copyFile(scrFile, new File(path,"screenshot_"+date+".jpg"));
    } catch (IOException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    }
}

instead of screenshot_ i want the test case name.