Java Programming Question and Answers

25. What is URL Naming Service?
  • URL naming service is a simple mechanism that lets a server object associates its Interoperable Object Reference (IOR) with a URL in the form of a string in a file.
  • Client programs can then locate the object using the URL pointing to the file on the web server.
  • In this scenario, a gate keeper is not necessary. The URL naming service supports any URL that Java runtime supports, such as HTTP, FTP.
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26. Explain the Bootstrapping technique in RMI?
  Bootstrapping technique provides the usage of a special class loader (such as RMI's class loader), instead o the default class loader, to download all the classes and interfaces needed by a client application during the RMI runtime.
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27. What are the CORBA services?
  CORBA services are collections of system-level services packaged with IDL specified interfaces. The services can be used to create a component, name a component, and introduce a component into the environment. OMG has published standards for 15 object services:
  • Life Cycle Service – Defines operations for creating, copying, moving, and deleting components on the bus.
  • Persistence Service – provides a single interface for storing components persistently on a variety of storage servers including RDBMSs and simple files, etc.
  • Naming service – Allows components on the bus to locate other components by name.
  • Event Service – Allows components on the bus to dynamically register or unregister their interest in specific events. It defines well known event channel that collects and distributes events among components that know nothing of each other.
  • Concurrency Control service – Provides a lock manager that can obtain locks on behalf of either transactions or threads.
  • Transaction Service – Provides two phase commit coordination among recoverable components using either flat or nested transactions.
  • Relationship Service – Provides a way to create dynamic associations or links between components that know nothing of each other.
  • Externalization Service – Provides a standard way for getting data into and out of a component using a stream like mechanism.
  • Query Service – Provides query operations for objects. It's a superset of SQL.
  • Licensing Service – Provides operations for metering the use of components to ensure fair compensation for their use.
  • Properties Service – Provides operations that let you associate named values with any component.
  • Time Service – provides interfaces for synchronizing time in a distributed object environment.
  • Security Service – Provides a complete framework for distributed object security. It supports authentication, access control lists, confidentiality, etc.
  • Trader Service – Provides yellow pages for objects; it allows objects to publicize their services and bid for jobs.
  • Collection Service – provides CORBA interfaces to generically create and manipulate the most common collection.
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28. What does the so called Event Channel consists of?
  The event channel consists of consumer proxy and supplier proxy. The actual supplier objects and consumer objects are completely decoupled from one another through the use of proxy objects.
Instead of directly interacting with each other, they obtain a proxy object from the event channel and communication with it. The supplier obtains a consumer proxy and consumer objects obtain a supplier proxy.
Thus the event channel facilitates the data transfer between consumer and supplier proxy objects.
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