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Remote Method Invocation (RMI)

Remote Method Invocation (RMI). IST 411 Lecture 8 Spring 2004. List. A collection is a data structure, an object, that can hold references to other objects. One collections-framework interface is a List

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Remote Method Invocation (RMI)

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  1. Remote Method Invocation (RMI) IST 411 Lecture 8 Spring 2004

  2. List • A collection is a data structure, an object, that can hold references to other objects. • One collections-framework interface is a List • Frameworks include a number of features that minimize the amount of coding programmers need to do to create and manipulate collections • Members of the package java.util.*

  3. List • A List (sometimes called a sequence) is an ordered Collection that can contain duplicate elements • Index is zero based • Interface List may be implemented by class ArrayList • ArrayList is a resizable-array implementation of a List • ArrayList execute faster than Vectors

  4. Remote Method Invocation • Remote method invocation • Distributed systems technology • One JVM invokes object methods that will run on another JVM on a network • Used in development of large-scale systems • Distribute resources and processing load across multiple machines

  5. Remote Method Invocation • Before object-oriented programming, technology used was Remote Procedure Calls (RPC). • Developed by Sun Microsystems • Designed as a platform-neutral way of communicating between applications • Operating system or language independent

  6. Remote Method Invocation • Difference between RPC and RMI: • Java is platform-neutral language • Java applications conceivably able to communicate with Java applications running on any hardware or operating system that supports JVM • RMI only support applications written in Java • RPC supports multiple languages

  7. Remote Method Invocation • RMI systems are divided into two categories: • Clients – invokes object methods of the server • Servers – provides an RMI service • RMI servers must register with a lookup service so clients can find them • Java platform has an application called rmiregistry which runs as a separate process • Allows applications to register RMI services

  8. Remote Method Invocation • Once a server is registered, waits for incoming RMI requests from clients

  9. Remote Method Invocation • RMI clients send RMI messages to invoke an object method remotely • Client needs remote object reference • Normally obtained from the RMI registry • Format of an RMI remote object reference: rmi://hostname:port/servicename • Hostname represents name of a server (or IP address) • Port is the location of the service on that machine; default port number for RMI registry is 1099 • Servicename is a string description of the service

  10. Remote Method Invocation • Networking details of requests are transparent to application developer • Remote objects seem like local objects • Achieved through division or RMI system into two components: • Stub – acts as a proxy object; RMI service is defined as an interface, not as an implementation • Skeleton – responsible for listening for incoming RMI requests and passing them on to the RMI service

  11. Remote Method Invocation • The stub is derived by compiling the remote object class using the rmic compiler • Utility supplied with J2SE SDK • A stub class forwards method invocations to the RMI layer; performs network communication to invoke method call on the remote object • In Java 1.1, rmic produced 2 classes – a stub class and a skeleton class • Java 2 no longer requires the skeleton class

  12. Remote Method Invocation • Messages are sent between the stub and skeleton using TCP sockets • Skeleton listens for incoming socket requests • When stub passes a request, it must package parameters • Either primitive datatypes, objects, or both • Called data marshalling • Skeleton reconstitutes parameters…unmarshalling • Use specialized subclasses of ObjectOutputStream and ObjectInputStream classes • Parameters are passed by value

  13. Remote Method Invocation • RMI Service Interface • Service interface defines the object methods that can be invoked remotely • Specifies parameters, return types, and exception that may be thown • All RMI service interfaces extend java.rmi.Remote • Common exception is: throws java.rmi.RemoteException which could occur when the system is down

  14. Compiling and Executing • Compiling and executing the server and client • Compile the classes • Compile the remote object class using the rmic compiler rmic –v1.2 <name of the Java file> • Start the RMI registry rmiregistry • Make the remote object available to receive remote method calls, bind the object to the name in the RMI registry java <application>

  15. Compiling and Executing • Run the client program java <client program name> • If the remote application is running on a different machine from the client, you can specify the IP address or host name on the command-line java <client program name> <IP address>

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