Vakgroep Informatietechnologie - IBCN CORBA & RMI Design of Distributed Software

2 ODS – Introduction to CORBA & RMI Vakgroep Informatietechnologie - IBCN Objectives After this lab session you should be able to Write client and server applications Devlop object-oriented based distributed systems Use the CORBA and Java RMI technology CORBA = Common Object Request Brokerage Architecture Language neutral technology Allowing software components on multiple computers to communicate Java RMI Java specific technology Allowing software components on multiple computers to communicate 2

ODS – Introduction to CORBA & RMI Vakgroep Informatietechnologie - IBCN CORBA & Java RMI Distributed system

4 ODS – Introduction to CORBA & RMI Vakgroep Informatietechnologie - IBCN Outline 1. CORBA How to write a CORBA application

5 ODS – Introduction to CORBA & RMI Vakgroep Informatietechnologie - IBCN Writing CORBA in 5 steps Writing the IDL files Writing the Server Writing the Servant Writing the Client Starting the application

6 ODS – Introduction to CORBA & RMI Vakgroep Informatietechnologie - IBCN Writing the IDL files The IDL file describes Which classes can be accessed remotely The signature of each remote method Compile the file: idlj –fall server.idl module ods{ module corba{ module bmicalculator{ interface BMICalculator{ double calculateBMI(in double length, in double weight); };

7 ODS – Introduction to CORBA & RMI Vakgroep Informatietechnologie - IBCN Writing the Server Several classes were generated Writing the server Extending the abstract POA class No CORBA specific code is needed package ods.corba.bmicalculator; public class BMICalculatorImpl extends BMICalculatorPOA{ public double calculateBMI(double length, double weight){ return weight / (length * length); }

8 ODS – Introduction to CORBA & RMI Vakgroep Informatietechnologie - IBCN Writing the servant Servant: main class to start the server Steps to take: Initialize the ORB (Object Request Broker) Start the Server object java.util.Properties props = System.getProperties(); props.put("org.omg.CORBA.ORBInitialPort”, ); props.put("org.omg.CORBA.ORBInitialHost", 1049); ORB orb = ORB.init(new String[0], props); BMICalculatorImpl bmi_calc = new BMICalculatorImpl();

9 ODS – Introduction to CORBA & RMI Vakgroep Informatietechnologie - IBCN Writing the servant Find the Naming Service & Root POA Activate the Server object with the POA POA rootPOA = POAHelper.narrow(orb.resolve_initial_references("RootPOA")); NamingContext namingContext = NamingContextHelper.narrow(orb.resolve_initial_references ("NameService")); rootPOA.activate_object(bmi_calc); BMICalculator bmicalcRef = BMICalculatorHelper. narrow(rootPOA.servant_to_reference(bmi_calc));

10 ODS – Introduction to CORBA & RMI Vakgroep Informatietechnologie - IBCN Writing the servant Register the server object with the Naming Service Activate the POA and start the ORB 10 NameComponent nc = new NameComponent("BMICalculator", ""); NameComponent path[] = { nc }; namingContext.rebind(path, bmicalcRef); rootPOA.the_POAManager().activate(); orb.run();

11 ODS – Introduction to CORBA & RMI Vakgroep Informatietechnologie - IBCN Writing the client Steps to take: Initialize the ORB (Object Request Broker) Find the Naming Service java.util.Properties props = System.getProperties(); props.put("org.omg.CORBA.ORBInitialPort”, ); props.put("org.omg.CORBA.ORBInitialHost", 1049); ORB orb = ORB.init(new String[0], props); NamingContext namingContext = NamingContextHelper.narrow(orb.resolve_initial_references ("NameService"));

12 ODS – Introduction to CORBA & RMI Vakgroep Informatietechnologie - IBCN Writing the client Obtain a reference to the remote object Invoke a method just as a regular object NameComponent nc = new NameComponent("BMICalculator", ""); NameComponent path[] = { nc }; BMICalculator server = BMICalculatorHelper.narrow(ncRef.resolve(path)); System.out.println(server.calculateBMI(1.87, 75));

13 ODS – Introduction to CORBA & RMI Vakgroep Informatietechnologie - IBCN Starting the application Starting the Naming Service Starting the Server Starting the client 13 start orbd –ORBInitialPort 1049 start java ods.corba.bmicalculator. StartBMICalculatorServer java ods.corba.bmicalculator.client.BMICalculatorClient

14 ODS – Introduction to CORBA & RMI Vakgroep Informatietechnologie - IBCN Outline 2. Java RMI How to write a Java RMI application

15 ODS – Introduction to CORBA & RMI Vakgroep Informatietechnologie - IBCN Writing Java RMI in 5 steps Writing the remote Java interface Writing the Server Writing the Servant Writing the Client Starting the application Writing the policy file

16 ODS – Introduction to CORBA & RMI Vakgroep Informatietechnologie - IBCN Writing the remote interface Define the class as remote Extend Remote interface Define the available remote methods Add “ throws RemoteException ” 16 package ods.rmi.bmicalculator.server; import java.rmi.Remote; import java.rmi.RemoteException; public interface BMICalculatorServerInterface extends Remote { public double calculateBMI(double length, double weight) throws RemoteException; }

17 ODS – Introduction to CORBA & RMI Vakgroep Informatietechnologie - IBCN Implementing the remote interface No specific Java RMI code is needed 17 public class BMICalculatorServer implements ods.rmi.bmicalculator.server.BMICalculatorServerInterface{ public BMICalculatorServer() { super(); } public double calculateBMI(double length, double weight) throws RemoteException { return weight/(length*length); } Writing the Server

18 ODS – Introduction to CORBA & RMI Vakgroep Informatietechnologie - IBCN Writing the servant Servant: main class to start the server Steps to take: Initialize the Security Manager Start the Server object if (System.getSecurityManager() == null) { System.setSecurityManager(new SecurityManager()); } BMICalculatorServerInterface bmiCalc = new BMICalculatorServer(); BMICalculatorServerInterface stub = (BMICalculatorServerInterface) UnicastRemoteObject.exportObject(bmiCalc, 0);

19 ODS – Introduction to CORBA & RMI Vakgroep Informatietechnologie - IBCN Writing the servant Register the server with the Registry Registry registry = LocateRegistry.getRegistry(); String name = (args[0]==null)?args[0]:"BMICalculator"; registry.rebind(name, stub);

20 ODS – Introduction to CORBA & RMI Vakgroep Informatietechnologie - IBCN Writing the client Steps to take: Initialize the Security Manager Obtain a reference to the remote object Invoke a method if (System.getSecurityManager() == null) { System.setSecurityManager(new SecurityManager()); } Registry registry = LocateRegistry.(args[0]); BMICalculatorServerInterface calculator = (BMICalculatorServerInterface)registry.lookup(args[1]); System.out.println(calculator.calculateBMI(1.87, 75));

21 ODS – Introduction to CORBA & RMI Vakgroep Informatietechnologie - IBCN Writing a policy file Policy file needed to allow network communication 21 grant{ permission java.net.SocketPermission "*: ", "connect,accept"; };

22 ODS – Introduction to CORBA & RMI Vakgroep Informatietechnologie - IBCN Starting the application Starting the Registry Starting the Server Starting the client 22 rmiregistry [port] start java -Djava.security.policy=java.policy ods.rmi.bmicalculator.server.BMICalculatorServer BMICalculator java -Djava.security.policy=java.policy ods.rmi.bmicalculator.client.BMIClientProgram BMICalculator