CORBA Object Browser

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CORBA Object Browser

• Versatile DII lets you discover and use a CORBA
  object at runtime without compiling stubs

Article by Poornachandra G. Sarang Mohan
Rajagopalan From Java Developers Journal (Vol.
4, Issue 6, June 1999) Presentation by Lara J.
Bordick
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Background

• CORBA provides platform, location and
  implementation neutral architecture.
• Wanted to be able to use available CORBA services
  on the web.
• You might not know the properties of the service
  ahead of time.
• Dynamic Invocation allows you to learn the
  properties and use the services at runtime. (Like
  Reflection in Java)

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Dynamic Invocation Interface (DII)

• A CORBA object publishes its Interface Definition
  Language (IDL).
• The CORBA architecture has an Interface
  Repository (IR) that allows the CORBA object to
  publish its IDL.
• Client gets a reference to the server object and
  retrieves the IDL from the IR.
• The DII allows the user to invoke the methods on
  the server object.

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A Benefit

• Client can learn about services
• Sever/ Publisher can add new features to an
  object after deployment.
• So, developers can modify previously published
  objects without the need to recompile and
  redistribute client-side stubs.

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An Example

• CORBA application that acts as an on-line store
• Initial implementation allows customers to visit
  and make purchases but send payment via regular
  mail
• New implementation allows credit card payment
• Add a credit card purchase method to the server
  object
• If you used DII, then the client can discover
  the new method instead of having to get a new
  compiled stub

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Details How the CORBA Object Browser Works.

• Browser built with Java and JFC classes.
• User specifies a reference to an existing CORBA
  server object.
• Objects are known because they are registered
  with a CORBA Naming Service.

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The Naming Services

• An object is registered with the CORBA Naming
  Service using a bind or rebind to the ORB
• Client calls resolve_initial_reference() method
  of the ORB

or

• An object is registered with the URL Naming
  Service
• Client refers to a URL and clients can access
  objects on Orb's at different machines
• Publisher must publish a special file on a web
  server so the client can find it

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Interface Repository

• Stores IDL definitions for CORBA objects
• On-line database for storing the definition of
  the interfaces
• An example

/ File abcom.jr Date Sat Jan 30 065840
GMT0000 1999 User Administrator Dir
C\Objectbrowser/module bank interface
TermDeposit interface TermDeposti attribute
float Interest float Compute in float
Principal in short Period )
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User Interface
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User Interface Description

• User enters name of server object
• User clicks Introspect Button
• Object is located and the browser displays the
  IDL
• User clicks the Operation and Attribute Listing
  tab
• Various operations and attributes are displayed
• Click on an attribute to see its properties
• Click on a method to get a window where
  parameters can be set (no validation yet)
• Click on Invoke button to invoke the server
  method

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Browser Design
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Browser Design Description

• Composed of 7 public classes
• ObjectBrowser (main user interface)
• InputPanel, OutputPanel, StatusBar (interface
  components)
• BackEnd (CORBA related activities)
• AttributeDescription and OperationDescriptionTable
  (helper classes)

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Running the browser

• Browser is buit with JDK 1.1.5 and swing classes
• Batch file compiles all the source code
• Must start OSAgent, Naming Service, etc.
• Run object browser vbj -DORBservicesCosNaming
  -DSVnamerootABCOM -VBJclasspath SWINGPATH
  ObjectBrowser

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Conclusion

• DII is very complex
• DII is very versatile
• Article has complete implementation steps
• Source code available at www.JavaDevelopersJournal
  .com
• Good building block for real applications
• Still needs polishing before marketable on a
  large scale