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Java RMI

Java RMI. Distributed Systems IT332. Outline. Introduction to RMI RMI Architecture RMI Programming and a Sample Example: Server-Side RMI programming Client-Side RMI programming. method call. AnotherClass. SomeClass. returned object. computer 1. computer 2. RMI.

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Java RMI

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  1. Java RMI Distributed Systems IT332

  2. Outline • Introduction to RMI • RMI Architecture • RMI Programming and a Sample Example: • Server-Side RMI programming • Client-Side RMI programming

  3. method call AnotherClass SomeClass returned object computer 1 computer 2 RMI • Consider the following program organization: • RMI is one technology that makes this possible • Allows distributed java objects across the network • General Idea: • Instantiate an object on another machine • Invoke methods on the remote object

  4. RMI and other technologies • CORBA (Common Object Request Broker Architecture) • CORBA supports object transmission between virtually any languages • Objects have to be described in IDL (Interface Definition Language) • CORBA is complex and flaky • RMI is purely Java-specific • Java to Java communications only • As a result, RMI is much simpler than CORBA

  5. RMI Architecture RMI rmi registry RMI Client Program Server Program RMI Machine Boundary

  6. RMI Components • The RMI application contains the THREE components: • RMI Server: contains objects whose methods are to be called remotely. • RMI Client: gets the reference of one or more remote objects from Registry with the help of object • RMI Registry: is a naming service. RMI server programs use this service to bind the remote java object with the names. Clients executing on local or remote machines retrieve the remote objects by their name registered.

  7. Client Server Client Code RMI Object 1 8 4 5 Skeleton Stub 3 6 2 7 Network Invocation Lifecycle Invoke method via stub Returns response Calls actual method with args Returns response / exception Serializes arguments, transmit Receives, deserialises response Receives, deserialises arguments Serialises response, transmit

  8. Steps for Developing an RMI System • Define the remote interface • Develop the the server program by implementing the remote interface. • Develop the client program. • Compile the Java source files. • Generate the client stubs and server skeletons. • Run the RMI registry. • Run the remote server objects. • Run the client

  9. Step 1: Defining the Remote Interface • To create an RMI application, the first step is the defining of a remote interface between the client and server objects. /* SampleServer.java */ import java.rmi.*; public interface SampleServerextends Remote { public int sum(inta,int b) throws RemoteException; }

  10. Step 2: Develop the remote object and its interface • The server is a simple unicast remote server. • Create server by extending java.rmi.server.UnicastRemoteObject. • The server uses the RMISecurityManager to protect its resources while engaging in remote communication. /* SampleServerImpl.java */ import java.rmi.*; import java.rmi.server.*; import java.rmi.registry.*; public class SampleServerImplextends UnicastRemoteObject implements SampleServer { SampleServerImpl() throws RemoteException { super(); }

  11. Step 2: Develop the remote object and its interface • Implement the remote methods • The server must bind its name to the registry, the client will look up the server name. • Use java.rmi.Namingclass to bind the server name to registry. In this example the name call “SAMPLE-SERVER”. • In the main method of your server object, the RMI security manager is created and installed. /* SampleServerImpl.java */ public int sum(inta,int b) throws RemoteException { return a + b; } }

  12. /* SampleServerImpl.java */ public static void main(String args[]) { try { System.setSecurityManager(new RMISecurityManager()); //set the security manager //create a local instance of the object SampleServerImpl Server = new SampleServerImpl(); //put the local instance in the registry Naming.rebind("SAMPLE-SERVER" , Server); System.out.println("Server waiting....."); } catch (java.net.MalformedURLException me) { System.out.println("Malformed URL: " + me.toString()); } catch (RemoteException re) { System.out.println("Remote exception: " + re.toString()); } }

  13. Step 3: Develop the client program • In order for the client object to invoke methods on the server, it must first look up the name of server in the registry. You use the java.rmi.Naming class to lookup the server name. • The server name is specified as URL in the from ( rmi://host:port/name ) • Default RMI port is 1099. • The name specified in the URL must exactly match the name that the server has bound to the registry. In this example, the name is “SAMPLE-SERVER” • The remote method invocation is programmed using the remote interface name (remoteObject) as prefix and the remote method name (sum) as suffix.

  14. import java.rmi.*; import java.rmi.server.*; public class SampleClient { public static void main(String[] args) { // set the security manager for the client System.setSecurityManager(new RMISecurityManager()); //get the remote object from the registry try { System.out.println("Security Manager loaded"); String url = "//localhost/SAMPLE-SERVER"; SampleServerremoteObject = (SampleServer)Naming.lookup(url); System.out.println("Got remote object"); System.out.println(" 1 + 2 = " + remoteObject.sum(1,2) ); } catch (RemoteExceptionexc) { System.out.println("Error in lookup: " + exc.toString()); } catch (java.net.MalformedURLExceptionexc) { System.out.println("Malformed URL: " + exc.toString()); } catch (java.rmi.NotBoundExceptionexc) { System.out.println("NotBound: " + exc.toString()); } } }

  15. Step 4 & 5: Compile the Java source files & Generate the client stubs and server skeletons • Once the interface is completed, you need to generate stubs and skeleton code. The RMI system provides an RMI compiler (rmic) that takes your generated interface class and procedures stub code on its self. > javacSampleServer.java > javacSampleServerImpl.java > rmicSampleServerImpl > javacSampleClient.java

  16. Step 6: Start the RMI registry • The RMI applications need install to Registry. And the Registry must start manual by call rmiregisty. • The rmiregistry us uses port 1099 by default. You can also bind rmiregistry to a different port by indicating the new port number as : rmiregistry <new port> > rmiregistry • Remark: On Windows, you have to type in from the command line: > start rmiregistry

  17. Steps 7 & 8: Start the remote server objects & Run the client • Once the Registry is started, the server can be started and will be able to store itself in the Registry. > java SampleServerImpl > java SampleClient

  18. References • http://java.sun.com/docs/books/tutorial/rmi/index.html • http://docs.oracle.com/javase/tutorial/rmi/index.html • http://www.eg.bucknell.edu/~cs379/DistributedSystems/rmi_tut.html • http://www8.cs.umu.se/education/examina/Rapporter/471App.pdf

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