1. LECTURE 20: Distributed Computing
Broker and Middleware
Ivan Marsic
Rutgers University

2. Topics Middleware Broker Design Pattern
Java Remote Method Invocation (RMI)

3. Object Messaging via Middleware

4. Serialization / Marshalling
From software objects to a sequence of bits for network transmission
Computer A
Computer B
Client
Middleware
Middleware
List Sorter
List
Network

5. Middleware
Middleware is a collection of objects that offer a set of services related to object communication, so that extraneous functionality is offloaded to the middleware
To reduce the number of object’s responsibilities
In general, middleware is software used to make diverse applications work together smoothly

7. Middleware (a) (b) Object A Object B Middleware Object A Object B'

8. Broker Pattern
(a)
(b)

9. Broker Class Diagram
(c)

10. Client-Server RMI/RPC

11. Java RMI Example

12. Practical Issues Do not design for patterns first
Reaching any solution is the priority; solution optimization should be secondary
Refactor the solution to patterns
E.g., to reduce the complexity of the program’s conditional logic
Uncritical use of patterns may yield worse solutions!