If you configure the StrutsPrepareAndExecuteFilter class directly in web.xml, this function is useless, but if you write a listener to inherit this class, you can add your own logic in the postInit method to achieve expansion.
for example:
class MyPrepareAndExecuteFilter extends StrutsPrepareAndExecuteFilter{
protected void postInit(Dispatcher dispatcher, FilterConfig filterConfig) {
System.out.println("call back source code");
}
}
Then configure MyPrepareAndExecuteFilter into filter in web.xml.