RMI Basics

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RMI Basics
Celsina Bignoli bignolic_at_smccd.net
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Socket-based code components

• business logic
• user interface for client
• marshalling/demarshalling
• launch and configuration of the application
• robustness (load balancing, threading)

TAKEN CARE OF AUTOMATICALLY BY RMI
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RMI

• RMI was designed to make communications between
  two programs running in different JVMs as close
  as possible to method calls inside a single
  process
• relies on two objects that are automatically
  generated by the RMI compiler
• stub
• skeleton

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Stubs and Skeletons
Client
Server
Invokes methods implemented by server
Network
Stub
Skeleton
Marshalls data and sends invocation over the
network
Demarshalls data and invokes server method
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RMI Compiler (rmic)

• rmic is a command line compiler shipped as part
  of the JDK
• Usage
• rmic full class name including packages
• Example
• rmic com.ora.rmiexample.RMITest
• generates
• com.ora.rmiexample.RMITest_Stub
• com.ora.rmiexample.RMITest_Skel
• Use option -keep to generate the source code for
  the stub and skeleton classes

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Passing by Value vs. by Reference

• RMI distinguishes between
• Remote objects
• receive remote method invocations
• have a fixed location
• passed by reference
• Serializable objects
• location is not relevant to their state
• encapsulate data
• are mobile between JVMs
• passed by value
• primitive data types are passed by value
• objects that are not Serializable nor Remote
  cause an exception to be thrown

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Naming Service

• runs on a central server and functions like a
  phone book
• client must
• connect to naming service to find out where
  server is running
• connect to server
• stable applications
• simple APIs that change rarely

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RMI Registry

• Default naming service for the Sun version of the
  JDK
• Methods are defined in nava.rmi.Naming
• Names in it are formatted as
• //host-nameport-number/human-readable-name
• host-name name of the host where the RMI
  Registry run
• port-number port for the RMI registry
• human-readable-name name used by the registry to
  identify the server

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Architecture
Server
Client
Printer
network
local connection
Registry
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Serialization

• process of transforming an object in a stream of
  bytes
• classes intended to be serialized must implement
  the Serializable interface
• class must be obviously serializable or
• declared transient
• implement readObject() and writeObject() methods
  to be used by the serialization algorithm.
• obviously serializable is a class which
  references primitive values or classes that are
  serializable