You need to write two parts for the server, an implementation class and a main method. These can be in the same class or separated for clarity.
The server-side code has to do a bit more work; see the sidebar.
This implementation divides the server into the traditional two parts, a main program and an implementation class. It is just as feasible to combine these in a single class. The main program shown in Example 22-3 simply constructs an instance of the implementation and registers it with the lookup service.
Example 22-3. DateServer.java
package darwinsys.distdate;
import java.rmi.*;
public class DateServer {
public static void main(String[] args) {
// You may want a SecurityManager for downloading of classes:
// System.setSecurityManager(new RMISecurityManager( ));
try {
// Create an instance of the server object
RemoteDateImpl im = new RemoteDateImpl( );
System.out.println("DateServer starting...");
// Locate it in the RMI registry.
Naming.rebind(RemoteDate.LOOKUPNAME, im);
System.out.println("DateServer ready.");
} catch (Exception e) {
System.err.println(e);
System.exit(1);
}
}
}The Naming.bind( )
method creates an association between
the lookup name and the
instance of the server object. This method will fail if the server
already has an instance of the given name, requiring you to call
rebind( )
to overwrite it. But since
that’s exactly where you’ll find yourself if the server
crashes (or you kill it while debugging) and you restart it, many
people just use rebind( ) all the time.
The implementation class must implement the given remote interface. See Example 22-4.
Example 22-4. RemoteDateImpl.java
package darwinsys.distdate;
import java.rmi.*;
import java.rmi.server.*;
import java.util.*;
public class RemoteDateImpl extends UnicastRemoteObject implements RemoteDate
{
/** Construct the object that implements the remote server.
* Called from main, after it has the SecurityManager in place.
*/
public RemoteDateImpl( ) throws RemoteException {
super( ); // sets up networking
}
/** The remote method that "does all the work". This won't get
* called until the client starts up.
*/
public Date getRemoteDate( ) throws RemoteException {
return new Date( );
}
}Once you’ve compiled the implementation class, you can run rmic (RMI compiler) to build some glue files and install them in the client’s CLASSPATH:
$ jikes -d . RemoteDateImpl.java $ ls darwinsys/distdate DateApplet$1.class DateClient.class RemoteDate.class DateApplet.class DateServer.class RemoteDateImpl.class $ rmic -d . darwinsys.distdate.RemoteDateImpl $ ls darwinsys/distdate DateApplet$1.class DateServer.class RemoteDateImpl_Skel.class DateApplet.class RemoteDate.class RemoteDateImpl_Stub.class DateClient.class RemoteDateImpl.class $
You must also ensure that TCP/IP networking is running, and then start the RMI registry program. If you’re doing this by hand, just type the command rmiregistry in a separate window, or start or background it on systems that support this.