The RMI Registry

The RMI registry is a very important part of the RMI communication. Without it there is no remote method invocation possibly. Normally you have to start the RMI registry manually as a separate program which ships with the JDK or JRE (Java Runtime Environment), but you can also start it automatically from your application. To start the RMI registry manually has a few advantages. It is separate from the Agent System. When the Agent System goes down the RMI registry keeps running and is able to serve other Agent Systems residing on this machine. If the registry is built in one Agent System and there are more Agent Systems running on the same machine, the others loose their capability to communicate through RMI when the System with the RMI registry is going down. The disadvantages are the following. First it is easier to use the built in registry because this does not require any user input. The built in registry is automatically started when no other RMI registry is running. The second advantage is the use of different ports for the RMI registry. The standard port is 1099 but if you have more then one application running on the same machine which is using the RMI services, it is a good idea to start different registry for the different applications. These registry are listening on different ports. If you use the built in registry (which is recommended) you can give a port in the configuration file and do not have to worry about the other registries running on the same machine with e.g. different CLASSPATHs. It could be a task for the future to re-run a new RMI registry if an Agent System cannot connect to the one running on its machine. This would be a very fail - safe construct.