what are the testNg Listeners?where did we use testng listeners? code example

Example: what is listener in testng

Listener annotation is used in selenium to generate logs or customize the 
TestNG reports.
We have to add first <listeners> class-name="Listener"/> tag into our 
testng.xml file. Then create a Listener class which implements ITestListener 
interface and override all the abstract methods from there. 
The Listener class can be under any folder however Utilities package is 
more proper to store it. 

ITestListener has  methods like:
- onStart- OnStart method is called when any Test starts.
- onTestSuccess- onTestSuccess method is called on the success of any Test.
- onTestFailure- onTestFailure method is called on the failure of any Test.
- onTestSkipped- onTestSkipped method is called on skipped of any Test.
- onTestFailedButWithinSuccessPercentage- method is called each time Test fails 
but is within success percentage.
- onFinish- onFinish method is called after all Tests are executed