1. The road to reliable, autonomous distributed systems
Jini Tutorial
The road to reliable, autonomous distributed systems

2. Tutorial outline Three parts, each (hopefully) one hour
Part 1 Introduction
Distributed systems
Java basics
Remote Method Invocation (RMI)
Part 2 Overview of Jini
Goals
Architecture
Basic concepts, protocols
Part 3
Jini Programming
Part 4 Advanced topics
Mobile Jini access
Adaptive user interfaces
Security

3. Characteristics of distributed systems
Different from closed-box systems
The followings are not true
Zero network latency
Networks are reliable
Remote systems fault-free
Infinite bandwidth
One administration
Homogeneous systems
Other problems
Systems can be very large – many components and services
Software deployment problems – packaging and distributing, upgrading

4. Why Java? The Java Language has many good design features
secure, safe (with respect to bugs), object-oriented, familiar (to C C++ and even Fortran programmers).
Good set of libraries
networking, multimedia, from graphics to math functions.
Higher programmer productivity
Best available electronic and paper training resources.

5. Why Java?
Java is rapidly getting the better (the best!) Integrated Development Environments (IDEs) for programs.
Java is naturally integrated with network and universal machine supports potentially powerful “write once-run anywhere” model.
Supports mobile code
Easy to teach, so there is a large and growing trained labour force.
First language in most CS course

6. Java: Key Technical Ideas
A Better Language:
Simplicity and C/C++ compatibility promote fluency;
GC and Threads allow software components;
Platform independence saves time;
Strong typing catches errors up front;
Declared exceptions forces coverage in code.
Scalable Applications;
Threads for parallel speedup; patterns “in the large”.
Dynamic linking allows simple apps to grow;
Range of implementations from JavaCard through J2ME (mobile) to J2EE (enterprise).

7. Java Virtual Machine (JVM)
The Java Platform
Consists of:
The Java Virtual Machine (Java VM)
The Java Application Programming Interface (Java API)
Java program
Java API
Java Virtual Machine (JVM)
Hardware platform
Java platform

8. The Java Architecture The Java programming language interpreted
portable and architecture independent

9. The role of mobile code Mobile code enables: Summary
Service provisioning, simple code/service deployment
Device and user specific dynamic user interfaces
Application/service composition on the fly
Summary
Java is good but not enough!

10. Missing from the Java language
Access to remote JVMs (RMI)
Ad hoc networking and dynamic system configuration (Jini)

11. Tutorial outline Part 1 Introduction Part 2 Overview of Jini Part 3
Distributed systems
Java basics
Remote Method Invocation (RMI)
Part 2 Overview of Jini
Goals
Architecture
Basic concepts, protocols
Part 3
Jini Programming
Part 4 Advanced topics
Mobile Jini access
Adaptive user interfaces
Security

12. Remote Method Invocation (RMI)
Java variant of Remote Method Invocation
Designed for Client-Server applications over unstable and slow networks.
Allows objects running on one JVM invoke methods on an object running on another JVM.
The basic object model of Java does not permit invocations on objects located in remote address spaces
Provides easy access to objects existing on remote virtual machines. RMI extends the basic Java object model beyond a single VM address space.
RMI provides (and hides) communication between remote Java programs.
Fast remote method invocations with low latency and high bandwidth are required for high performance computing.

13. Java RMI Model cont’d
Objects can be passed as arguments and returned as results
remoteObject.someMethod( objectArgument );
Any Java object can be passed during invocation including primitive types, core classes, user-defined classes and JavaBeans
Syntax of remote method invocation is same as the local invocations
RMI operates only in Java-Java domain, developers work within a single object model instead of working with multiple models
RMI-IIOP to other systems

14. Basic components Client machine Server machine stub skeleton
HTTP
HTTP
Client machine
Server machine
Rmi registry
Client code
Lookup / download
stub
skeleton
remote server

15. Required operations in distributed object applications
Register/Locate remote objects:
Obtain references to remote objects . An application can register its remote objects with RMI's simple naming facility, the rmiregistry, or the application can pass and return remote object references as part of its normal operation.
Communicate with remote objects:
Details of communication between remote objects are handled by RMI; to the programmer, remote communication looks like a standard Java method invocation.
Load class bytecodes for objects that are passed around:
Because RMI allows a caller to pass objects to remote objects, RMI provides the necessary mechanisms for loading an object's code, as well as for transmitting its data.

16. Object Serialization
Provides a programmer the ability to read or write a whole object to and from a raw byte stream.
An essential feature needed by RMI implementation when method arguments are passed by copy.

17. Development Steps
Design and implement components of distributed application.
Define remote interface – specifies functionality as remote methods.
Implement remote objects – implement the remote interface.
Implement clients.
Compile sources and generate stubs and skeletons.
No skeletons from v1.2
Put classes in Web accessible directory (HTTP).
Start registry, start application.

18. Main problem Static system configuration Solution is Jini
Client needs service name/IP address
Makes server/service replication impossible
Difficult to handle errors (network or server)
Solution is Jini