ClientServer Using RMI

1
Client/Server Using RMI

• Joe Komar

2
Remote Method Invocation (RMI)

• Can invoke methods on a remote object
• Integrates a distributed object model
• ORB compliant
• Extends security allowing dynamic downloading of
  stub classes
• Passes local objects by value (serialization)
• Passes remote objects by reference

3
RMI Process (ten steps to success)

• Define an interface -- extends java.rmi.Remote,
  all methods throw java.rim.Remote.Exception
• Implement the interface -- server class that
  extends java.rmi.UnicastRemoteObject
• Compile the server class
• Run the stub compiler -- rmic classname
• Generates stub for client and skeleton for server

4
RMI Process (ten steps to success)

• Start the RMI registry (non-persistent naming
  service) -- rmiregistry
• Start the serve objects -- load server classes
  and create instances of remote objects
• Register your remote objects with the registry --
  use java.rmi.Naming class methods

5
RMI Process (ten steps to success)

• Write your client code -- use java.rmi.Naming
  class to locate remote object
• Compile the client code
• Start the client

6
RMI Interface
// CountRmi Interface public interface CountRMI
extends java.rmi.Remote int sum() throws
java.rmi.RemoteException void sum(int _val)
throws java.rmi.RemoteException public int
increment() throws java.rmi.RemoteException
7
RMI Interface Implementation
// CountRMIImpl.java, CountRMI implementation impo
rt java.rmi. import java.rmi.server.UnicastRemot
eObject public class CountRMIImpl extends
UnicastRemoteObject implements CountRMI
private int sum
8
RMI Interface Implementation
public CountRMIImpl(String name) throws
RemoteException super() try
Naming.rebind(name, this) sum 0 catch
(Exception e) System.out.println("Exception
" e.getMessage()) e.printStackTrace()

9
RMI Interface Implementation
public int sum() throws RemoteException
return sum public void sum(int val)
throws RemoteException sum val
public int increment() throws RemoteException
sum return sum
10
RMI Server
// CountRMIServer.java import java.rmi. import
java.rmi.server. public class CountRMIServer
public static void main(String args)
System.setSecurityManager(new RMISecurityManager()
) try CountRMIImpl myCount new
CountRMIImpl("my CountRMI")
System.out.println("CountRMI Server ready.")
catch (Exception e) System.out.println("Exc
eption " e.getMessage())
e.printStackTrace()
11
RMI Client
// CountRMIClient.java RMI Count client import
java.rmi. import java.rmi.registry. import
java.rmi.server. public class CountRMIClient
public static void main(String args) //
Create and install the security manager
System.setSecurityManager(new RMISecurityManager()
)
12
RMI Client
try CountRMI myCount (CountRMI)Naming.lookup("
rmi//" args0 "/"
"my CountRMI") System.out.println("Setting Sum
to 0") myCount.sum(0) long startTime
System.currentTimeMillis() System.out.println("
Incrementing") int count new
Integer(args1).intValue() for (int i 0 i
lt count i ) myCount.increment()
13
RMI Client
long stopTime System.currentTimeMillis()
System.out.println("Avg Ping "
((stopTime - startTime)/(float)count
) " msecs")
System.out.println("Sum " myCount.sum())
catch(Exception e) System.err.println("Sys
tem Exception" e) System.exit(0)

14
RMI Example Output
On the Server Count RMI Server ready. On the
Client Setting sum to 0 Incrementing Avg Ping
14.83 msecs Sum 500
15
RMI Hands On

• There are four files in \\Nt431\Public\komar\rmi
  that you need to copy to your diskette
• On one system find the IP name (Start/Run
  WINIPCFG)
• Copy the files to a temporary directory on that
  server
• Use this directory as your home directory for the
  steps on the next page

16
RMI Hands On

• Compile the ...Server java program which should
  compile all the classes needed for the server
• Run the RMI compiler using the Impl file
• rmic CountRMIImpl
• Copy the _Stub.class file to the diskette
• Run the RMI registry (start rmiregistry)
• Run the server (java CountRMIServer)

17
RMI Hands On

• Take your diskette to a second machine and do
  these steps.
• Compile the Client.java program
• Run the client using the IP name as the first
  parameter and an iteration integer as the second
• java CountRMIClient s152.sci1.stthomas.edu 500

18
RMI Related classes and interfaces

• RemoteException -- superclass for all RMI
  exceptions. All remote methods must throw a
  RemoteException
• Remote -- interface that flags remote objects
  (contains no methods)
• RemoteObject -- remote version of the Java root
  Object class
• RemoteServer -- class to define methods to create
  server objects and export them

19
RMI Related classes and interfaces

• UnicastRemoteObject -- class implements a remote
  server object
• object only exists as long as the process that
  created it
• requires a TCP connection based transport
• client and server use a stream protocol to
  communicate
• RemoteStub -- class is superclass for all client
  stubs

20
RMI Related classes and interfaces

• Registry interface -- methods let you update
  entries in a registry
• LocateRegistry class -- overloaded getRegistry()
  static methods to find a registry
• Naming class -- retrieve and define remote
  objects using URL syntax
• rmi//hostport/name (port usually 1099)
• Client uses lookup() method, host uses rebind()
  method

21
RMI Related classes and interfaces

• RMISecurityManager class -- simple security
  manager for RMI objects (Applets have their own
  security classes)
• RMIClassLoader class -- load stubs and skeletons
  via a URL

22
RMI and CORBA (Common Object Request Broker
Architecture)

• Moving toward one way in cooperation with OMG
  (Object Management Group consortium)
• RMI over IIOP (Internet InterORB Protocol) --
  will be offered by JavaSoft
• RMI/IDL (Interface Definition Language) -- use
  Java syntax to specify CORBA interfaces

23
RMI Assignment

• Create the Java code needed to do the following
  using RMI
• Perform addition, subtraction, multiplication, or
  division by executing a remote objects method
• That remote method will accept three parameters
  (character operator, double val1, double val2)
  and return the resulting double