Jini and Legacy Systems

Jan Newmarch
University of Canberra
DSTC

Jini

• Jini is "network plug and work"
• Based on Java
• Treats h/w and s/w as "services" with "clients"
• Uses mobile code
• Distributed event and transaction models

Legacy

• Jini has been available for one year
• Jini mailing list: "Jini has stalled"
• CNet: "What is holding up Sun's much-hyped technology?"
• How can Jini establish itself and grow in legacy environments?

Seminar

• Overview of Jini
• Jini in a Jini environment
• Jini in legacy environments
  • Legacy clients with Jini services
  • Jini clients with legacy services

Service Lookup Discovery

• Broadcast to discover Lookup Service
• LUS = (naming service + trader)/2

Lookup Service Discovered

• LUS transfers an object to the service
• Service transfers a "dormant" proxy to the LUS

Client Lookup Discovery

• Client discovers LUS in the same way as any service
• "discovering" != "being discovered"
• Separation of concerns!

Client Search

• Search based on object types
• Type safety!

Client-Service Communication

• Can use RMI proxy/stub
• Can have no communication
• Can use own client-server protocol
• Flexibility!

Distributed Events

• Any service/client can act as event generator
• Any client/service can register as event listener
• A client/service can register another as event receiver

Lookup Service Events

• Events are generated on changes in the LUS knowledge of services
• Service added events
• Service removed events
• Service properties changed events

Service Events

• Services/clients can generate RemoteEvent's
• The meaning depends on the generator

MindStorms

Jini in a Jini World

• The Jini specification deals with Jini services and Jini clients
• It covers interaction between services and clients
• It doesn't cover interactions between clients and users
• It doesn't specify services

Jini Desktop?

• Speculation at present

Interfaces

• No interfaces yet defined!

Service UI Project

• Led by Bill Venners of Artima Software
• Allows definition of multiple UI's per service
• UI attached to service, not part of the service
  
• The service UI interface will go to Jini Community voting soon

Printer Interface Project

• Led by Alan Kaminsky of Xerox Corp
• Based on the Internet Printing Protocol (IPP)
• IPP is just a protocol - the proposal adds classes, interfaces, types, methods
• The printer interface will go to Jini Community voting soon

Legacy

• What single application helped Microsoft Windows to succeed?
   
• What single application helped X Windows to succeed?
   

Legacy

• What single application helped Microsoft Windows to succeed?
  the DOS box
• What single application helped X Windows to succeed?
  multiple xterm's

Jini and Legacy

• Legacy clients with Jini services
  • M/S Word using a Jini printer
  • Web browser accessing a Jini service
• Jini clients with legacy services
  • Jini wordprocessor with Unix printer service lpr
  • Jini client driving MindStorms robot

Jini Services with Legacy Clients

• Few known efforts
• JTAW
• Jini and SAP
• Jini URL's

Jini Technology Adapter for Windows

• Proposal from Printing group, by Alan Kaminsky
• JTAW supplies a "network provider", similar to NFS network provider or Print network provider
• The JWAT network provider communicates with a JWAT gateway that interacts with Jini services
• These give the ability to "browse" Jini services from Windows
• Extended to provide print services from Jini printer to Windows
• Status: in alpha (September, 1999). Now defunct?

Jini and SAP

• Projects in definition stage between DSTC and SAP
• The coke machine continuously on the network
• The coke machine on spontaneous Bluetooth networks

Coke on the Network

• The Coke machine is permanently connected to the network
• It broadcasts "change of state" events to a listener which does a batch update on a SAP inventory

Coke on Bluetooth

• The PDA joins the adhoc Bluetooth network around the Coke machine
• It interrogates the Coke machine for state, and passes this up to the SAP system by WAP

Jini URL's

• "Jini services as URL's" project, still in formation stage
• Scope is undecided as to "Jini in Jini" or "Jini services in legacy"
• I have proposed a "Jini services in legacy" scheme, or "Jini services via HTTP"

Jini Services via HTTP

• Control your airconditioning system from your browser!

Jini Clients with Legacy Services

• Surrogate project
• Client Server and Jini
• CORBA and Jini

Surrogate Project

• In "discussion of ideas" phase
• Allows non-Jini devices to join a Jini "device bay"
• Clients look up a "surrogate" service and make requests on it
• Partly driven by failure from Sun to supply a KVM supporting Jini

Client Server and Jini

• Client-server systems often suffer from version control problems when the service is upgraded
• Web browsers are extreme examples
• By exporting the client-side as a Jini service, maintenance is simplified

CORBA

• CORBA (Common Object Request Broker Architecture) is middleware for distributed systems
• A CORBA system is specified by a language-independant Interface Definition Language (IDL)
• There are language bindings from CORBA IDL to C, C++, Java, SmallTalk, Cobol, Ada, Python, etc
• Clients and "servants" communicate by remote procedure call, using the CORBA backplane
• Code mobility as in Java is in the latest CORBA specifications

CORBA and Jini

• Bridges can be built between CORBA (over IIOP) and Jini
• Due to shared TCP transport protocol, there are several ways bridging can be done
• Captured in "design patterns"
• Should be possible to automatically generate bridges from the IDL

CORBA/Jini using thin Jini Proxies

Conclusion

• In order to be successful, Jini must progress on three fronts
  • Jini clients with Jini services
  • Legacy clients with Jini services
  • Jini clients with legacy services
• Some interfaces are close to standardisation, but much needs to be done
• Sun needs to complete the KVM with Jini support
• It is still early: Linux took 8 years to get accepted, Java is still a bit "nouveau" after only 5 years
• The Australian Jini Centre aims to provide a showcase of examples in each category, and encourage research and development in this area