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Remote Method Invocation
RMI
Distributed Object Applications
• RMI applications are often comprised of two
separate programs:
– A server
– A client
• Distributed object applications need to:
– Locate remote objects
– Communicate with remote objects
– Load class bytecodes for objects that are passed as
parameters or return values
RMI Layers
RMI Development
Process
Differences
• The Java platform's distributed object model differs
from the Java platform's object model in these ways:
– Clients of remote objects interact with remote interfaces, never with the
implementation classes of those interfaces.
– Non-remote arguments to, and results from, a remote method invocation are
passed by copy rather than by reference. This is because references to objects
are only useful within a single virtual machine.
– A remote object is passed by reference, not by copying the actual remote
implementation.
– The semantics of some of the methods defined by class java.lang.Object are
specialized for remote objects.
– Since the failure modes of invoking remote objects are inherently more
complicated than the failure modes of invoking local objects, clients must deal
with additional exceptions that can occur during a remote method invocation.
RMI Interfaces and Classes
• java.rmi package hierarchy :
– java.rmi.
– java.rmi.server
– java.rmi.registry
RMI Core (1)
• Remote interface
– Does not define any methods. Every Remote objects must implement
this interfaces
• RemoteException class
– the superclass of exceptions thrown by the RMI runtime during a
remote method invocation.
-------------------------------------------------------------------------------------------import java.rmi.*;
public interface yourOwnDefinedService extends java.rmi.Remote
{
// declare yourOwnDefinedMethods
public int method1 ( int number )
throws RemoteException;
…………………….
}
RMI Core (2)
• UnicastRemoteObject class
– Class implement a remote server object with the following
characteristics:
• All references to the remote objects are only valid during the life
time of the process that create the remote object
• The remote protocol requires a TCP connection
• Client/server communicate parameters, invocations, and results
using a stream protocol
import java.math.*;
import java.rmi.*;
import java.rmi.server.*;
public class yourOwnDefinedServiceServer extends UnicastRemoteObject
implements yourOwnDefinedService
{
public yourOwnDefinedServiceServer () throws RemoteException {
super();
}
// implement the methods
public int method1 ( int number )
throws RemoteException {
//implementation of method here ...
}
// ....... probably more method implementation here
public static void main ( String args[] ) throws Exception{
// Assign a security manager
// Create an instance of our power service server ...
// ... and bind it with the RMI Registry
}
}
RMI Core (3)
import java.rmi.*;
import java.rmi.Naming;
import java.io.*;
public class yourOwnDefinedServiceClient
{
public static void main(String args[]) throws Exception{
……….
// Assign security manager
// Call registry for PowerService
………..
}
RMI Naming
RMI Security