Question

I have an applet that communicates with a servlet using Http (Not sockets). Currently, each instance of the applet (i.e. when each applet is run by a different client on a different computer), all the instances communicate with the same servlet. What I want is that each instance of the applet communicate with different instances of the same servlet. Is this possible?

Answer 1

You don’t want to have different instances of the same servlet in webapp’s lifetime. The normal practice is to use the HttpSession to distinguish between clients. You need to pass the HttpSession#getId() as parameter to the applet in question:

<param name="jsessionid" value="${pageContext.session.id}">

Then, in the Applet connect the Servlet as follows:

String jsessionid = getParameter("jsessionid");
URL servlet = new URL(getCodeBase(), "servleturl;jsessionid=" + jsessionid);
URLConnection connection = servlet.openConnection();
// ...

Here servleturl obviously should match servlet’s url-pattern in web.xml. You can alternatively also set a Cookie request header using URLConnection.setRequestProperty().

Finally, in the Servlet, to get and store client specific data, do as follows:

// Store:
request.getSession().setAttribute("data", data);
// Get:
Data data = (Data) request.getSession().getAttribute("data");

Hope this helps.