Recipe 22.2 Creating an RMI Client

Problem

You want to write a client to use an RMI service.

Solution

Locate the object and call its methods.

Discussion

Assume for now that the server object is running remotely. To locate it, you use Naming.lookup( ) , passing in the lookup name. This gives you a reference to a proxy object , an object that, like the real server object, implements the remote interface but runs in the same Java Virtual Machine as your client application. Here we see the beauty of interfaces: the proxy object implements the interface so that your code can use it just as it would use a local object providing the given service. And the remote object also implements the interface so that the proxy object's remote counterpart can use it exactly as the proxy is used. Example 22-2 shows the client for the RemoteDate service.

Example 22-2. DateClient.java

package darwinsys.distdate; import java.rmi.*; import java.util.*; /* A very simple client for the RemoteDate service. */ public class DateClient {     /** The local proxy for the service. */     protected static RemoteDate netConn = null;     public static void main(String[] args) {         try {             netConn = (RemoteDate)Naming.lookup(RemoteDate.LOOKUPNAME);             Date today = netConn.getRemoteDate( );             System.out.println(today.toString( )); //  Could use a DateFormat...         } catch (Exception e) {             System.err.println("RemoteDate exception: " + e.getMessage( ));             e.printStackTrace( );         }     } }

Also in the online source rmi directory are DateApplet.htm and DateApplet.java, which together provide an example of using the server. In DateApplet, the connection is set up in the applet's init( ) method. The actual RMI call to get the date is done in the action handler for the push button so that you can refresh it on demand.