RMI How can a Client reconnect to a server after connection(any)-error

Question

I have the following problem:
My RMI-Server runs for ever. In a batch-queue I have a procedure which looks periodly wether rmiregistry
and RMI-Server exists. On error both processes are killed and restarted.
My client as a simple example is displaying the server time. If any communication-problem with the
server exists, I need an automatic reconnect to the server. I accept that into the time distanz of the
error the display is frozen. Its unacceptable to restart the client !!.
The following example demonstates my test-example:
Server:
1. Start
2. waits for connecting (factory)
3. answer time-requests
Client:
1. Start
2. create a time class initially 1.jan.1970 00:00:00
3. Start a timer displaying the time class every second
4. start a timer connecting/reconnecting to the server and ask the servers actual time every second
PS. Is the server to stubil programmed, so that a hang can exists?
It would be nice, if anybody could answer me !!
The following sources work correctly without solving the problem of the reconnect:
////////////// Echo.java
package emi.server;
import java.rmi.*;
import java.util.*;
public interface Echo
extends Remote
public Date getTime() throws RemoteException;
////////////// EchoClient.java
package emi.server;
//import emi.utility.basics.*;
public class EchoClient
public static void main(String args[]) throws Exception
EchoClient echoclient1 = new EchoClient();
//Check the argument count
if (args.length != 1)
System.err.println("Usage: EchoClient <server> --> EXIT");
System.exit(0);
// all of time relevant things
Etim acttim = new Etim();
// displaying continous the time
EchoClientDisplay disp = new EchoClientDisplay(acttim);
disp.StartTimer();
// transfering continous the time from the server
EchoClientTransfer trans = new EchoClientTransfer(acttim, args[0]);
trans.StartTimer();
////////////// EchoClientDisplay.java
package emi.server;
import java.awt.event.*;
import javax.swing.*;
// displaying every 750 Milliseconds the value of the time
public class EchoClientDisplay implements ActionListener
private Timer tim;
private Etim tact;
public EchoClientDisplay(Etim tact)
tim = new Timer(750, this);
this.tact = tact;
public void StartTimer()
tim.setRepeats(true);
tim.setInitialDelay(5);
tim.start();
public void actionPerformed(ActionEvent e )
System.out.println(tact.toString());
////////////// EchoClientTransfer.java
package emi.server;
import java.rmi.Naming;
import java.rmi.RMISecurityManager;
import java.awt.event.*;
import javax.swing.Timer;
import java.util.Date;
// transferring the actual time from the server
public class EchoClientTransfer implements ActionListener
private Etim tact;
private String hostname;
private Timer tim;
private boolean init = false;
private Echo echoRef1 = null;
public EchoClientTransfer(Etim tact, String hostname)
this.tact = tact;
this.hostname = hostname;
this.tim = new Timer(500, this);
public void StartTimer()
tim.setRepeats(true);
tim.setInitialDelay(5);
tim.start();
public void actionPerformed(ActionEvent e )
//>>>>>>>>>>> this construction doesnt work correctly, its only good until the first
// network error
try
if( init == false )
// Create and install the security manager
System.setSecurityManager(new RMISecurityManager());
//get the remote factory object from the registry
String url = new String("rmi://"+ hostname +"/EchoFactory");
EchoFactory remoteFactory = (EchoFactory)Naming.lookup(url);
//get references to new EchoImpl instances
echoRef1 = remoteFactory.getEcho("User Meyer");
init = true;
if( init = true )
//make the remote calls
Date d = echoRef1.getTime();
tact.setDate(d);
catch(Exception ee)
System.out.println(ee.toString());
init = false;
//<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<
////////////// EchoFactory.java
package emi.server;
import java.rmi.RemoteException;
import java.rmi.Remote;
public interface EchoFactory extends Remote
Echo getEcho(String userName) throws RemoteException;
////////////// EchoFactoryImpl.java
package emi.server;
import java.rmi.RemoteException;
import java.rmi.server.UnicastRemoteObject;
public class EchoFactoryImpl extends UnicastRemoteObject implements EchoFactory
EchoFactoryImpl() throws RemoteException {};
public Echo getEcho(String userName) throws RemoteException
EchoImpl echoRef = new EchoImpl(userName);
return (Echo)echoRef;
////////////// EchoImpl.java
package emi.server;
import java.rmi.RemoteException;
import java.rmi.server.UnicastRemoteObject;
import java.util.*;
public class EchoImpl extends UnicastRemoteObject implements Echo
private String userName;
public EchoImpl() throws RemoteException
public EchoImpl(String userName) throws RemoteException
this.userName = userName;
public Date getTime()
Etim e = new Etim();
e.setTimeAct();
return e.get();
////////////// EchoServer.java
package emi.server;
import java.rmi.Naming;
import java.rmi.RMISecurityManager;
public class EchoServer
public static void main(String args[]) throws Exception
// Create and install the security manager
System.setSecurityManager(new RMISecurityManager());
// Create the servant instance for registration
EchoFactory factoryRef = new EchoFactoryImpl();
// Bind the object to the rmiregistry
Naming.rebind("EchoFactory", factoryRef);
System.out.println("Echo object ready and bound to the name 'EchoFactory'!");
////////////// Etim.java
package emi.server;
import java.util.*;
import java.text.*;
// this is my central class working up all time problems .. many hundred lines of code
// I think, you must not look at this code ist setting and reading time
// this is only a subset of methods for this example
public class Etim
private Date dat;
private Calendar cal;
public Etim()
cal = Calendar.getInstance(); // Gregorianischer Kalender
dat = new Date(0L); // January 1, 1970, 00:00:00
cal.clear();
* Zeit lesen.
public Date get()
return dat;
// setting the time
public void setDate( Date d )
dat.setTime( d.getTime() );
cal.setTime(dat);
// gets my time-class to the current system-clock
public void setTimeAct()
long millis;
millis = System.currentTimeMillis();
setMilli(millis);
* Zeit setzen.
public void setMilli(long millis)
dat.setTime(millis);
cal.setTime(dat);
// time in german format: day.month.year hour:minute:second:millisecond
public String toString()
return toStringTagMoJahr() + " " + toStringStdMiSek() +
":" + cal.get(Calendar.MILLISECOND);
* Ausgabeformat Tag.Monat.Jahr (z.B. 01.01.2001).
public String toStringTagMoJahr()
SimpleDateFormat s = new SimpleDateFormat("dd.MM.yyyy");
return s.format(dat);
* Ausgabeformat Stunde:Minute:Sekunde (00:00:00 - 23:59:59).
public String toStringStdMiSek()
SimpleDateFormat s = new SimpleDateFormat("HH:mm:ss");
return s.format(dat);

Answer 1

Hello willy51,
Thank you for answering.
I think, your comment of the design is true - its a problem when starting up in a new enviroment and
you have nobody who shows you the right direction at the beginning. Talking personally together only
10 minutes is better than writing a noval.
I thing the following model of a client works better:
concept:
- visualize a personal time class continously evgery second
- if there is a connection to a server set the time-class with the server time
- if you loss connection, try to reconnect
question:
in which situation hangs connectToServer() ?
(whithout the simple errors : no rmiregistry, no rmi-server)
public class EchoClient
private String hostname;
public static void main(String args[]) throws Exception
// my internal TIME-Class
Etim acttim = new Etim();
// Create and install the security manager
System.setSecurityManager(new RMISecurityManager());
// remote call
Echo echoRef1 = null;
String url = new String("rmi://"+ servername:port +"/EchoFactory");
// displaying continous the time, technic = swing.timer
EchoClientDisplay disp = new EchoClientDisplay(acttim);
disp.StartTimer();
// transfering continous the time from the server, technic = swing.timer
// The state of transfer from server = offline
EchoClientTransfer trans = new EchoClientTransfer(acttim);
trans.StartTimer();
// Connect to server
connectToServer(url, echoRef1, trans);
// wait for ever, if connection failed, try every 5 seconds a reconnect to server
while(true)
// test, if connection failed. The connections fails if the Object EchoClientTransfer
// get a error, when it asks the server for the time ( remote call )
if(trans.getStatus() == false ) // test, if connection failed
connectToServer(url, echoRef1, trans);
// try it again after 5 seconds
Thread.sleep(5000);
private static void connectToServer(String url, Echo echoRef1, EchoClientTransfer trans)
System.out.println("Retry connection");
// Connect to server
while( true )
try
//get the remote factory object from the registry
EchoFactory remoteFactory = (EchoFactory)Naming.lookup(url);
//get references to new EchoImpl instances
echoRef1 = remoteFactory.getEcho("User Meyer");
// reactivate Datatransfer because I have now a new connection to the server
trans.reactivateAfterConnectionError(echoRef1);
// end of initialisation
break;
catch( Exception e )
//>>>>>>> Error initialising connection to server. try again after 5 seconds"
Thread.sleep(5000); // retry after 5 seconds