Question

Fill in the blanks in each of the following statements: a) Name three required services for running Jini services and clicnts: __________,__________and _________. b) Two ways to discover lookup services are ________ and _________ c) To generate the stub file for a remote object, use ________ d) A service proxy that is exported to the remote client must implement interface________ e) Service providers use________to describe a service. Jini clients use__________to find a matching service.

Short answer

a) Lookup Service, Discovery Service, and Join Service; b) Multicast and Unicast; c) `rmic`; d) Remote; e) ServiceItem, ServiceTemplate.

Step-by-step solution

Identify Required Services for Running Jini

Jini requires specific services to operate correctly. These services include a directory of available network objects, the ability to register new network objects, and mechanisms for clients to locate these objects. The three essential services are: Lookup Service, Discovery Service, and Join Service.

Discover Lookup Services

Lookup services in Jini can be discovered in two primary ways: Multicast and Unicast. Multicast is used on the local network to find services automatically. Unicast allows a client to contact a specific address for discovering services.

Generating Stub File for Remote Object

In Java RMI (Remote Method Invocation), the `rmic` command-line tool is used to generate stub files for remote objects. These stubs act as proxies to enable communication between the client and the remote object.

Implementing Service Proxy Interface

When a service proxy is exported to a remote client in Jini, it must implement the `Remote` interface. This interface ensures that the proxy can handle remote method calls.

Describing and Finding Jini Services

Service providers in Jini use an interface called `ServiceItem` to describe a service. Jini clients use `ServiceTemplate` to find a matching service. The template acts as a query to search for services with specific attributes.

Key concepts

Lookup Service

In the world of Jini technology, the Lookup Service acts like a central hub that connects service providers and clients. Just imagine it as a directory listing where all available services can register themselves so that clients can discover and interact with them.

This Lookup Service performs two main functions:

• It allows service providers to register their services so others can find them. Think of it as adding your name and contact to a phone book.
• It acts as a reference point for clients who are searching for services. Clients query the lookup service to retrieve a list of services that match their requirements.

By using the Lookup Service, Jini-enabled devices and applications can work together seamlessly, enabling services to be provided, discovered, and utilized across a network. This service is vital for the smooth operation of Jini technology, essentially knitting the ecosystem together.

Discovery Service

The Discovery Service in Jini plays a fundamental role by helping clients find lookup services efficiently. Think of it like the GPS guiding a traveler to the right location. Without it, clients might find it challenging to discover where to look for services within the network.

There are two prevalent methods for this discovery to happen:

• Multicast Discovery: This method involves broadcasting a request to find lookup services available on the local network. It's like sending an open invitation to find all nearby parties.
• Unicast Discovery: In contrast, unicast targets a specific address to find a lookup service. It's akin to sending a letter directly to a known address.

These mechanisms ensure that even in a large and dynamic environment, clients and devices can easily locate services and start interacting with them almost immediately.

Java RMI

Java RMI (Remote Method Invocation) is the thread that connects remotely running objects. It's a Java mechanism that enables an object residing in one Java virtual machine to invoke methods on an object in another JVM.

Here’s how Java RMI integrates with Jini technology:

• When a service proxy is to be used remotely, it needs to implement Java's `Remote` interface. This ensures that it can handle invocations from remote clients.
• To communicate effectively, stub files must be generated, which act as intermediaries. These are created using the `rmic` tool, preparing all necessary details to facilitate the remote call seamlessly.

Thus, Java RMI with Jini helps in building a distributed environment where various services can communicate and deliver functionality across networks effortlessly.