Jan Newmarch
jan@ise.canberra.edu.au
University of Canberra
DSTC (Distributed Systems Technology CRC)

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Jini and MindStorms

• Jini brings ``network plug and play'' to hardware devices and software services
• Jini is in pure Java
• It makes hardware and software available as Java networked services
• ``Legacy'' systems can be wrapped in a Java proxy
• Jini has competitors including CORBA Trader, DCOM, HP's Chai, Enterprise Java Beans, JNDI, etc

• A Jini federation or ``djinn'' consists of a number of clients, services and service locators
• Typically connected by TCP/IP
• Code is moved around from service to locator to client using Java 1.2 extensions to RMI

Figure 1: Components of a Jini federation

Figure 2: Querying for a service locator

Figure 3: Registrar returned

Figure 4: Service uploaded

Figure 5: Querying for a service locator

Figure 6: Registrar returned

Figure 7: Asking for a service

Figure 8: Service returned

• Jini objects are moved in ``marshalled'' form
• Class files may need to follow these for proper activation
• The class files may need to be available from HTTP servers
• RMI Naming can be used to locate remote objects
• RMI Naming may need an rmiregistry or rmid running
• Security permissions will need to be set using JDK 1.2 security model

• A toaster will be controlled by some service software
• The service software will be moved across the network to the client
• The mobile code must be a proxy for the real service code
• The proxy may be explicitly written or be an RMI proxy stub
• Remote calls from the proxy may be RMI Remote calls, or by some other mechanism such as private TCP connection

• A service is uploaded to a locator as an instance of a class
• Additional information such as address may also be uploaded as instances of Entry classes
• Service registration is done using a leasing system

• A client asks for a service as an instance of a class, typically of an interface
• A client may ask for additional Entry attributes
• Matching on fields is exact
• You can ask for a printer with a certain speed, but not for one greater than a certain speed
• Additional services may be used if complex boolean expressions are needed

• Objects moved around must be serializable
• Some common objects are not serializable e.g. Swing Toolbar, Swing JTextArea
• Objects with DLLs are not serializable e.g. MPEG players
• JDK 1.2 memory requirements are enormous compared to JDK 1.1
• Jini v1.0 has some bugs
• Limited documentation

MindStorms is a ``Robotics Invention System''

• A 16-bit computer called the RCX (a 16MHz Hitachi H8/3297), with 32k RAM
• The RCX can control 3 motors and read from 3 sensors
• Additional Lego parts - gears, wheels, sensors, motors
• Software can be downloaded by an infra-red link on a serial port
• Programs can be downloaded and run, or ``immediate'' commands can be run
• Normally programmed from a visual programming environment or from VB
• On a PC, interface to RCX is managed by an OCX
• Low-level machine-code is sent across the IR link

• Encapsulate client-side in a convenience class
• Make the ``Not Quite C'' RCX compiler available as a Jini service
• Make the RCX ``network aware'', by using e.g. an alternative O/S such as LegOS

• Build bridges to other network services (CORBA Trader, JNDI, etc)
• Interface to other network protocols and implementations (BlueTooth, HomeRF, etc)
• Design standard interfaces to service types
• Build Jini proxies for hardware and software services
• Build embedded Jini engines (in Java or other languages) for hardware devices
• How does ``service architecture'' differ from client-server, CORBA, etc?

• Jini: http://www.jini.org
• Jini FAQ: http://www.artima.com/jini/faq.html
• Lego MindStorms: http://www.legomindstorms.com
• Unofficial Lego MindStorms: http://www.crynwr.com/lego-robotics/
• Jini tutorial: http://pandonia.canberra.edu.au/java/jini/tutorial/Jini.xml
• Motorola Piano: http://www.mot.com/GSS/SSTG/piano/