LECTURE 20: Distributed Computing Broker and Middleware http://en.wikipedia.org/wiki/Problem_Frames_Approach Ivan Marsic Rutgers University

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

Object Messaging via Middleware

Serialization / Marshalling From software objects to a sequence of bits for network transmission Computer A Computer B Client Middleware Middleware List Sorter List Network 010110011

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

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

Broker Pattern (a) (b)

Broker Class Diagram (c)

Client-Server RMI/RPC

Java RMI Example

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!