How do I send information and data back and forth between applet and servlet using the HTTP protocol?

Answer 1

Use the standard java.net.URL class, or “roll your own” using java.net.Socket. See the HTTP spec at W3C for more detail.

Note: The servlet cannot initiate this connection! If the servlet needs to asynchronously send a message to the applet, then you must open up a persistent socket using java.net.Socket (on the applet side), and java.net.ServerSocket and Threads (on the server side