Java Servlet Programming

Acting as an RMI Client

In Chapter 10, we saw how a servlet can act as an RMI server. Here we turn the tables and see a servlet acting as an RMI client. By taking the role of an RMI client, a servlet can leverage the services of other servers to accomplish its task, coordinate its efforts with other servers or servlets on those servers, and/or act as an proxy on behalf of applets that can’t communicate with RMI servers themselves.

Example 13.8 shows DaytimeClientServlet, a servlet that gets the current time of day from the DaytimeServlet RMI server shown in Chapter 10.

Example 13-8. A servlet as an RMI client

import java.io.*; import java.rmi.*; import java.rmi.registry.*; import javax.servlet.*; import javax.servlet.http.*; public class DaytimeClientServlet extends HttpServlet { DaytimeServer daytime; // Returns a reference to a DaytimeServer or null if there was a problem. protected DaytimeServer getDaytimeServer() { // Set the security manager if it hasn't been done already. // Provides protection from a malicious DaytimeServer stub. if (System.getSecurityManager() == null) { System.setSecurityManager(new RMISecurityManager()); } try { Registry registry = LocateRegistry.getRegistry(getRegistryHost(), getRegistryPort()); return (DaytimeServer)registry.lookup(getRegistryName()); } catch (Exception e) { getServletContext().log(e, "Problem getting DaytimeServer reference"); return null; } } private String getRegistryName() { String name = getInitParameter("registryName"); return ...