1.) Create a simple HTML form where users are able to charge their mobile phones with a given amount of money.

 Possible amounts: $10, $30, $50, $100 
 The 3 mobile service providers: "Provider A", "Provider B", "Provider C"
 Mobile phone number: 7 numbers.

2.) Create a servlet which gets the HTTP GET request from the HTML form and checks the validity of the messages. If the message is invalid, then returns an “Invalid data” text, else writes “Ok”.

3.) Create an inner class within servlet and store these payments in a java ArrayList.

4.) Create an other method to list the number of payments (with a new HTTP get request).