RMI

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RMI

• Remote Method Invocation

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Client - Server

• Server creates remote objects
• Client manipulates the servers objects
• (ie invokes methods)

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Distributed Object ApplicationWhats Required?

• client-server communication
• protocol
• remote references

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• locate remote objects
• pass/return remote object references
• register remote objects via RMI registry
• communicate with remote objects
• handled by the RMI facilities (mostly
  transparent to the user)
• pass objects
• transmit data and class definitions

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Distributed Application RMI

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RMI FeatureDynamic Code Loading

• transfer
• data (objects)AND
• classes (definitions)
• Why is this a feature?

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How?

• Java application
• Interfaces
• define methods
• Classes
• implement interface methods and, possibly, other
  methods
• Distributed
• some implementations reside on different JVMs

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Remote Objects

• definition
• objects with methods that can be invoked across
  different JVMs
• How to make an object remote
• implement a remote interface
• extends the interface java.rmi.Remote
• each method declares java.rmi.RemoteException(in
  the throws clause)

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• RMI passes a remote stub
• local representative (proxy)
• client sees this as the remote reference
• client invokes a method on the stub
• stub carries out the invocation on the remote
  object

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Steps for a Distributed Application using RMI

• design, implement the components
• compile
• make classes network accessible
• start the application

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1. Design, Implementation

• Determine local, remote components
• define remote interfaces
• implement remote objects
• implement clients

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2. compile

• javac
• versions prior to Java Platform, Standard Edition
  5.0 require use of the rmic compiler

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3. Network Accessibility

• run
• RMI remote object registry

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4. Start the application

• run
• server
• client

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Example(from Java trails)

• Compute Engine
• remote object
• client server
• new tasks can be created on the fly(aka
  behavior-based application)