Presentation 13: RMI continued – more advanced issues: Activation & RMI over IIOP

1. Presentation 13:RMI continued – more advanced issues: Activation & RMI over IIOP

2. Goals of this lesson • After this 1x35 lessons you will be • Introduced to Activation framework and rmid • Introduced to RMI over IIOP

3. Outline • Theory: (35 min.) • The Java RMI Activation framework (UDGÅR!) • Java RMI over IIOP

4. Architecture coded manually Client Server lookup bind Registry Activation Stub Skeleton Interfaces Interfaces rmic generated rmic generated RMI Runtime ( rmid ,rmiregistry )

5. Experience from the HelloWorld tutorial • What happens after we create the server implementation object and bind it to the registry? • For how long does this object remain in memory? • When is this a clever approach? • When is this not the case • What is our options? • =>RMI Activation

6. Activation • Smart for objects that are rarely used • And in systems with MANY object • Solves problem running a large number of idle RMI services • Allows for registering without getting instantiated • Not smart for objects with frequent use • Needs to save and load state on persistent storage = performance degrading

7. How it works • Remote method invocation activation system daemon (rmid) – listening for request • Services lie dormant until invoked then activated • Faulting reference from rmiregistry instead of service – has two • ActivationID: identifies the service • Liveref: when service is activated, a life reference • Faulting reference via rmid invokes service by first call • ActivationGroup ties the class with the rmid daemon – more ActivationID’s per group. 1 Group = 1 JVM

8. Architecture coded manually Client Server lookup bind NEW: register Registry Activation Stub Skeleton Interfaces Interfaces rmic generated rmic generated RMI Runtime ( rmid ,rmiregistry )

9. Activation in Java Java VM Stub Java VM 2 1 2: create object Faulting in VM Reference Live Activa- 3: pass ref tion ID object ref AG AG 1 2 Activator 1: activate Activation Descriptors: ActGroup ClassName URL Init AG Team www.bvb.de/… 1 AG Player www.bvb.de/… 2 AG Player www.bvb.de/… 2 4: update AG Player www.bvb.de/… 2 live ref Client Host Host www.bvb.de

10. package examples.hello; import java.rmi.*; import java.rmi.activation.*; public class HelloImpl extends Activatableimplements Hello { public HelloImpl (ActivationID id, MarshalledObject data)throws RemoteException { super(id, o); } public String sayHello() { return "Hello World! ; } } Server object (HelloImpl.java) Client and interface Hello does not change!!! Register the object with the activation system then export it on an anonymous port

11. package examples.hello; import java.rmi.*; import java.rmi.activation.*; import java.util.Properties; public class Setup { public static void main(String[] args) throws Exception { System.setSecurityManager(new RMISecurityManager()); Properties props = new Properties(); props.put("java.security.policy", "policy"); ActivationGroupDesc.CommandEnvironment ace = null; ActivationGroupDesc exampleGroup = new ActivationGroupDesc(props, ace); ActivationGroupID agi = ActivationGroup.getSystem().registerGroup(exampleGroup); String location = "file:/C:/dev/examples/activation/"; MarshalledObject data = null; ActivationDesc desc = new ActivationDesc(agi, "examples.activation.HelloImpl",location, data); MyRemoteInterface mri = (MyRemoteInterface) Activatable.register(desc); Naming.rebind(“HelloImpl", mri); System.exit(0); } } Setup.java – contact with rmid & registry Because of the 1.2 security model, a security policy must be specified for the ActivationGroup VM. grant { // Allow everything for now permission java.security.AllPermission; }; Once the ActivationGroupDesc has been created, register it with the activation system to obtain its ID Register with the rmid daemon Register the class (bind it) in the ”rmiregistry” BUT DO NOT INSTANTIATE! HelloImpl obj = new HelloImpl(); // Bind this object instance to the name "HelloServer" Naming.rebind("rmi://192.168.1.101/HelloServer", obj);

12. RMI over IIOP - CORBA 2.3-> • Java RMI uses the Java Remote Method Protocol (JRMP) • This protocol is open – but not supported by many • Using the Interoperable Inter-ORB protocol (IIOP) makes RMI compatible with other IIOP technologies – like CORBA - IIOP • With some restrictions • This is done in the J2EE EJB technology (IIOP comes with a price – not as many features + narrow needed) • Allows for using CORBA services – like the orbd Naming Service

13. RMI over IIOP – implementation • http://java.sun.com/j2se/1.4.2/docs/guide/rmi-iiop/ Interface – no changes //HelloInterface.java import java.rmi.Remote; public interface HelloInterface extends java.rmi.Remote { public void sayHello( String from ) throws java.rmi.RemoteException; } //HelloImpl.java import javax.rmi.PortableRemoteObject; public class HelloImpl extends PortableRemoteObject implements HelloInterface { public HelloImpl() throws java.rmi.RemoteException { super(); // invoke rmi linking and remote object initialization } public void sayHello( String from ) throws java.rmi.RemoteException { System.out.println( "Hello from " + from + "!!" ); System.out.flush(); } } Implementation a bit foreign

14. RMI over IIOP – Name binding //HelloServer.java import javax.naming.InitialContext; import javax.naming.Context; public class HelloServer { public static void main(String[] args) { try { // Step 1: Instantiate the Hello servant HelloImpl helloRef = new HelloImpl(); // Step 2: Publish the reference in the Naming Service // using JNDI API Context initialNamingContext = new InitialContext(); initialNamingContext.rebind("HelloService", helloRef ); System.out.println("Hello Server: Ready..."); } catch (Exception e) { System.out.println("Trouble: " + e); e.printStackTrace(); } } } JNDI: Java Naming and Directory Service – decoupling of Naming Service (e.g. orbd) InitialContext -> contact to server

15. //HelloClient.java import java.rmi.RemoteException; import java.net.MalformedURLException; import java.rmi.NotBoundException; import javax.rmi.*; import java.util.Vector; import javax.naming.NamingException; import javax.naming.InitialContext; import javax.naming.Context; public class HelloClient { public static void main( String args[] ) { Context ic; Object objref; HelloInterface hi; try { ic = new InitialContext(); // STEP 1: Get the Object reference from the Name Service // using JNDI call. objref = ic.lookup("HelloService"); System.out.println("Client: Obtained a ref. to Hello server."); // STEP 2: Narrow the object reference to the concrete type and // invoke the method. hi = (HelloInterface) PortableRemoteObject.narrow( objref, HelloInterface.class); hi.sayHello( " MARS " ); } catch( Exception e ) { System.err.println( "Exception " + e + "Caught" ); e.printStackTrace( ); return; } } } We still use “lookup” but now we Use the ”initial context” from the Naming services (ORB) We call narrow because this Object is only valid in the server VM – ”narrow” one to this VM

16. Getting it up and Running • Compile with javac • Run rmic • rmic –iiop HelloImpl • Run Naming Service • E.g. use orbd tool (persistent naming) • start orbd -ORBInitialPort 1050 • Start the HelloServer • java -classpath . -Djava.naming.factory.initial=com.sun.jndi.cosnaming.CNCtxFactory -Djava.naming.provider.url=iiop://localhost:1050 HelloServer • Start the Client • java -classpath . -Djava.naming.factory.initial=com.sun.jndi.cosnaming.CNCtxFactory -Djava.naming.provider.url=iiop://localhost:1050 HelloClient

17. Restrictions in RMI over IIOP • To make existing RMI programs run over IIOP, you need to observe the following restrictions. • Make sure all constant definitions in remote interfaces are of primitive types or String and evaluated at compile time. • Don't use Java names that conflict with IDL mangled names generated by the Java to IDL mapping rules. See section 28.3.2 of the Java Language to IDL Mapping specification for the Java to IDL name mapping rules. • Don't inherit the same method name into a remote interface more than once from different base remote interfaces. • Be careful when using names that differ only in case. The use of a type name and a variable of that type whose name differs from the type name only in case is supported. Most other combinations of names that differ only in case are not supported. • Don't depend on runtime sharing of object references to be preserved exactly when transmitting object references across IIOP. Runtime sharing of other objects is preserved correctly. • It is not possible to use the following RMI features when using IIOP: • RMISocketFactory • UnicastRemoteObject • Unreferenced • The Distributed Garbage Collector (DGC) interfaces • Dynamic class loading via the network

18. How do I interoperate between an RMI-IIOP app - and an existing CORBA object? • If the existing CORBA object has its remote interfaces defined originally in CORBA IDL, then interoperability is not possible. RMI-IIOP applications can interoperate with other CORBA objects only when their remote interfaces are originally defined as Java RMI interfaces. • Also: Objects-by-value must be supported by all involved ORB’s • For example, to interoperate between an RMI-IIOP client and a C++ object you would need to: • define the remote interface of the object in Java as an RMI Interface • run rmic -iiop against the interface to produce the stub for your RMI-IIOP client • run rmic -idl against the interface to produce IDL compatible with the RMI interface • run a C++ stub compiler against the IDL file to produce the C++ skeleton for your C++ server object.

19. Alignment med læringsmål Når kurset er færdigt forventes den studerende at kunne: • redegøre for de grundlæggende principper og teknikker omkring interproceskommunikation over såvel lokalnetværk som Internettet • redegøre for teknikker for distribuerede objektorienterede løsninger, herunder serialisering, marshalling, stub/skeleton, proxy, brug af forskellige Interface Definition Language sprog som udviklingskontrakt • redegøre for principperne omkring transparens og heterogenitet (platforms og programmeringssprogs uafhængighed) • redegøre for anvendelsen af Java RMI, XML/SOAP (Webservices), herunder forskelle/ligheder, fordele/ulemper teknologierne imellem. Samt på overordnet niveau have kendskab til forskelle og ligheder med CORBA og .NET Remoting teknologierne • anvende socket programmering til at lave et mindre distribueret system baseret på objektorienterede principper • anvende objektorienterede teknikker og arkitekturer til at designe og programmere netværksforbindelser ved brug af middleware, og bevise dette ved at konstruere og dokumentere to distribuerede systemer der gør brug af ovenstående teknologier At kunne afgøre hvilken teknologi der skal vælges Java RMI er ikke kun JRMP baseret. Det bliver helt anderledes heterogent ved brug af IIOP. MEN – prisen er access transparency der falder lidt, mens location stiger en smule pga. mulighed for COS Naming. Her må .NET Remotings strategy siges at være bedre