Java Programming/Jini

Concurrent Programming topics

• Threads and Runnables
• Basic Synchronization
• Client Server Programming
• Remote Method Invocation(RMI)
• Enterprise JavaBean Programming
• Jini-Java Spaces Programming

JINI

After J2EE Sun had a vision about the next step of network computing. That is JINI. The main idea is that in a network environment, there would be many independent services and consumers. JINI would allow these services/consumers to interact dynamically with each other in a robust way. The basic features of JINI are:

• No user intervention is needed when services are brought on or offline. (In contrast to EJBs where the client program has to know the server and port number where the EJB is deployed. In JINI the client is supposed to find, discover the service in the network.)
• Self healing by adapting when services(consumers of services) come and go. (Services need to periodically renew a lease to indicate that they are still available.)
• Consumers of JINI services do not need prior knowledge of the service's implementation. The implementation is downloaded dynamically and run on the consumer JVM, without configuration and user intervention. (For example, the end user may be presented with slightly different user interface depending which service is being used at the time. The implementation of those user interface code would be provided by the service being used.)

This fact that the implementation is running on the consumer/client's JVM can increase performance, by eliminating the need of remote calls.

A minimal JINI network environment consist of:

• One or more services
• A lookup-service keeping a list of registered services
• One or more consumers

The jini Lookup Service

The lookup service is described in the : Jini Lookup Service Specification (reggie). This service interface defines all operations that are possible on the lookup service. Clients locate services by requesting with a lookup server that implements a particular interface. Client asks the lookup server for all services that implement the particular service interface. The lookup service returns service objects for all registered services that implement the given interface. The client may invoke methods on that object in order to interact directly with the server.

Lookup Discovery

Jini Discovery and Join Specification describes how does the client find the jini lookup service. There is a protocol to do that, jini comes with a set of API's that implement that protocol. The Jini Discovery Utility Specification defines a set of utility classes that are used to work with the protocol.

Leasing

When a service registers with the lookup service, it receives a lease from the lookup service, described in the Jini Distributed Leasing Specification.