CS 603 Jini April 10, 2002

What is Jini? Java Middleware Tools to construct federation –Multiple devices, each with Java Virtual Machine –Multiple services Uses (doesn’t replace) Java RMI Adds infrastructure to support distribution –Registration –Lookup –Security

Service Basic “unit” of JINI system –Members provide services –Federate to share access to services Services combined to accomplish tasks Communicate using service protocol –Initial set defined –Add more on the fly

Infrastructure: Key Components RMI –Basic communication model Distributed Security System –Integrated with RMI –Extends JVM security model Discovery/join protocol –How to register and advertise services Lookup services –Returns object implementing service (really a local proxy)

Programming Model Lookup Leasing –Extends Java reference with notion of time Events –Extends JavaBeans event model –Adds third-party transfer, delivery and timeliness guarantees, possibility of delay Transaction Interfaces

Jini Component Categories Infrastructure – Base features Programming Model – How you use them Services – What you build Java / Jini Comparison

Lookup Service Describes functionality Describes interface Lookup is a service –Can be referenced in another lookup service –Also register lookup with non-Jini naming Registering –Discovery protocol: Find a lookup service –Join protocol: Register with the lookup service

Registration

Sample Server public class SendHelloServer implements DiscoveryListener { protected LeaseRenewalManager leaseManager = new LeaseRenewalManager(); public static void main(String argv[]) { new SendHelloServer(); // keep server running to allow time for locator // discovery and keep re-registering the lease Thread.currentThread().sleep(Lease.FOREVER); } public SendHello() { LookupDiscovery discover = null; // Prepare for discovery - empty here // Discover a lookup service // This uses the asynchronous multicast protocol, // which calls back into the discovered() method discover = new LookupDiscovery( LookupDiscovery.ALL_GROUPS); discover.addDiscoveryListener(this); } public void discovered(DiscoveryEvent evt) { ServiceRegistrar registrar = evt.getRegistrars()[0]; // At this point we have discovered a lookup service // Create information about a service ServiceItem item = new ServiceItem(null, new SendHelloImpl(), null); // Export a service ServiceRegistration reg = registrar.register(item, Lease.FOREVER); // Renew leasing leaseManager.renewUntil(reg.getLease(), Lease.FOREVER, this); } } // SendHelloServer

Invocation

Sample Client public class Hello { public static void main(String argv[ ]) { new Hello(); } public Hello() { LookupLocator lookup = null; ServiceRegistrar registrar = null; FileClassifier classifier = null; // Prepare for discovery lookup = new LookupLocator( "jini:// // Discover a lookup service // This uses the synchronous unicast protocol registrar = lookup.getRegistrar(); // Prepare a template for lookup search Class[ ] classes = new Class[ ] {SendHello.class}; ServiceTemplate template = new ServiceTemplate( null, classes, null); // Lookup a service sender = (SendHello) registrar.lookup(template); // Call the service System.out.println( sender.SendHello()); } } // Hello

Security Principal: Authenticated user making request Access control list: What principals can use a service JVM security mechanisms ensure services don’t compromise local machine

Leasing Lease: Right to access a service –Guarantees access for specified time period Negotiated as part of service protocol Allows freeing resource by either end, without explicit negotiation –Fault tolerance Exclusive vs. Non-exclusive –Exclusive: Non-shared resource –Non-exclusive: Allows sharing resource

Transactions Operations can be wrapped in transaction –What is done in transaction is up to operation –Notion of what “commit” or “abort” means isn’t specified Abort may even change state of system! Jini provides two-phase commit protocol –Secure, fault tolerant commit / abort –No semantics enforced by Jini

Events Notification system Object must support/define events Other objects can register for notification Jini handles communication / reliability issues