CS 603Jini

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 Serverpublic 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 leaseThread.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() methoddiscover = 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 serviceServiceItem item = new ServiceItem(null, new

SendHelloImpl(), null);// Export a serviceServiceRegistration reg = registrar.register(item,

Lease.FOREVER);// Renew leasingleaseManager.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 discoverylookup = new LookupLocator(

"jini://www.simple_stuff.com");// Discover a lookup service// This uses the synchronous

unicast protocolregistrar = lookup.getRegistrar();

// Prepare a template for lookup search

Class[ ] classes = new Class[ ] {SendHello.class};

ServiceTemplate template = new ServiceTemplate(null, classes, null);

// Lookup a servicesender = (SendHello)

registrar.lookup(template);// Call the serviceSystem.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

specifiedAbort 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