app                // parent/root project folder
 |- src
 |- target
      |- app.war   // common features
 |- app-payment    // child/module folder
        |- src
        |- target
             |- app-payment.war  // shop/pay features

requests for
   localhost:8080/app/payment   --goto-->   $CATALINA_HOME/webapps/app-payment.war (or any other locations, doesn't matter)
other requests for
   localhost:8080/app           --goto-->   $CATALINA_HOME/webapps/app.war