1. Objektorienteret Middleware (TIOOMI) Presentation 20 : Value Types in CORBA

2. Agenda Design & Use of DTO’s Complex “class” types in IDL Internals of Valuetypes Mappings A few words of warning: Assumed students are knowledgeable about OOA/OOD We will only look at some aspects of distributed architecture Not much literature available on this subject No textbook solutions to this problem This lecture is just for inspiration – not a dictate

3. Design by Layering Client Presentation tier Provides a user interface to the end-users. Thin/Rich. MVC. Server Side Presentation tier Building a response to the Client Presentation tier. Server Side Business Logic tier Use Case implementation. Control classes. Business logic. Server Side Domain Model tier Domain Model. Entity classes. Enterprise Integration tier Legacy system. Web services. Persistence tier / Resource layer Relational Database. File-system. Using DTO’s Replicating Objects / Data Transfer Object Pattern How to do it in CORBA? -NOT IDL Interfaces -IDL Structs -IDL Valuetypes

4. Complex “Class” Types in IDL Interface CORBA Remote objects communicates “by reference” Holds attributes and operations (methods) Gives rise to the “round-tripping” anti-pattern IDL example: interface BankFacade Struct CORBA struct types are communicated “by value” Holds only attributes, no methods No support for inheritance Maps to “class” type in Java, but “struct” in C++ IDL example: struct Address Valuetype Objects that primarily communicates “by value” (hybrids exists) Holds both attributes AND methods, no POA, no Object ID Maps to “class” types in Java and C++ IDL example: valuetype Account By value By reference

5. But we Expected This! We would expect the ability to transfer objects “by value” in CORBA Java RMI has it,.NET Remoting has it, most SOAP implementation toolkits support it So – it should be really easy – right? It is not One need to implement varying amounts of code Depending on the ORB vendor & language mapping A bit of a drag – but not that hard

6. How does it work ClientServer InfoImpl 1) Instantiate an Info object and initialize it with data 2) Send request to interface Greetings – marshal Info object InfoImpl 3) Use Factory to create and initialize the object – unmarshalling. Find factory in factory table Example: - we have a “Greetings Interface (CORBA Object) receiving valuetype Info objects by value. This is a simple DTO pattern implementation Must “know” the InfoImpl implementation code 4) All method calls are performed strictly on the local copy. No marshalling is performed (e.g. setName(…)) Must “know” the InfoImpl implementation code IDL:Info:1.0 IDL:other:1:0 Info Factory Value Factory Table We need a mechanism for letting the ORB de-serialize the object – automatically, making a “local” instance of the Info object Unmarshals & instantiates

7. Valuetype module Valtype { valuetype Info { // explicit state to transport: private string _name; private string _message; // public interface: string toString(); // public Factory interface: factory create( in string name, in string message ); }; interface Greetings { // receives and returns an Info valuetype by value Info hello( in Info who); }; The Valuetype defined The Factory Interface for unmarshalling The “regular” CORBA Object

8. MiddCor C# Mapping Interface / classDescription public interface InfoValueFactory : Middsol.CORBA.portable.ValueFactory Generated – the interface for the value factory public abstract class Info : Middsol.CORBA.portable.StreamableValue Generated – an abstract class. This is the one we need to implement public class InfoHelperGenerated – the Helper class. Contains utility code. public class InfoDefaultFactory : InfoValueFactoryGenerated – a “default” factory, so that we need not bother do it ourselves. MiddCor does this for us as a service Also generated: all classes for the Greetings interface – but this will not be mentioned here Middcor generates: -All needed functionality for marshalling / unmarshalling -An abstract Info class The developer must: -Write an Info implementation class (InfoImpl)

9. MiddCor Generated Default Factory … public class InfoDefaultFactory : InfoValueFactory { public System.Object read_value( Middsol.CORBA.portable.InputStream ins ) { return ins.read_value( new InfoImpl() ); } public Info create( string a_name, string a_message ) { return (Info) new InfoImpl( a_name, a_message ); } … the “create” just calls the constructor Might be extended – if we need some initialization done

10. Abstract Info class public abstract class Info : Middsol.CORBA.portable.StreamableValue { protected string _name; protected string _message; abstract public string toString( ); virtual public void _write( Middsol.CORBA.portable.OutputStream outpStream ) { outpStream.write_string( this._name ); outpStream.write_string( this._message ); } virtual public void _read( Middsol.CORBA.portable.InputStream inpStream ) { this._name = inpStream.read_string(); this._message = inpStream.read_string(); } private static string[] __truncatable_ids = {InfoHelper.id()}; virtual public string[] _truncatable_ids() { return __truncatable_ids; } virtual public Middsol.CORBA.TypeCode _type() { return InfoHelper.type(); } From IDL definition No factory from IDL

11. Need to Implement InfoImpl Yourself namespace Valtype { public class InfoImpl: Valtype.Info { public InfoImpl() { } public InfoImpl( string name, string message ) { _name = name; _message = message; } public string name { set { _name = value; } get { return _name; } } public string message { set { _message = value; } get { return _message; } } public override string toString() { return "Info: " + _name + " says " + _message + " (client implementation)"; } Only _toString() needs to be overridden as this was the only abstract method You may add all the methods you like – if you need them locally. These may differ on server & client. Constructors necessary for factory

12. The C# Client public void run( string[] args) { try { m_oOrb = Middsol.CORBA._ORB.init( args, null); Middsol.CORBA.Object oGreetingsObj = m_oOrb.string_to_object( "file://c:\\Valuetype.ior"); Valtype.Greetings oGreetings = Valtype.GreetingsHelper.narrow( oGreetingsObj ); // Create parameter for server call: Valtype.InfoImpl oInfo = new Valtype.InfoImpl(); oInfo.name = "John"; oInfo.message = "The weather is fine!"; System.Console.WriteLine( "\nCall server with Info:\n {0}", oInfo.toString() ); Valtype.Info oRetInfo = oGreetings.hello( oInfo ); System.Console.WriteLine( "\nServer answered Info:\n {0}", oRetInfo.toString() ); m_oOrb.destroy(); } catch( Middsol.CORBA.UserException exUser) { Console.WriteLine("CORBA-UserException\n {0}", exUser.GetType().ToString()); } catch( Middsol.CORBA.SystemException exSys) { Console.WriteLine("CORBA-SystemException\n {0}", exSys.ID); } Instantiated an object & Initialize it with data Make the remote call and Get an InfoImpl returned Marshalling of valuetype here – and demarshalling at server using factory

13. The C# Server (Server & Impl in One Class!) public void run( string[] args) { try { m_oOrb = Middsol.CORBA._ORB.init( args, null); m_oRootPOA = Middsol.PortableServer.POAHelper.narrow( m_oOrb.resolve_initial_references( "RootPOA" )); m_oRootPOA.the_POAManager.activate(); GreetingsImpl oGreetings = new GreetingsImpl(); Middsol.CORBA._ORB.wrIORtoFile( "c:\\Valuetype.ior", oGreetings._this() ); System.Console.WriteLine("Server is running..." ); m_oOrb.run(); m_oOrb.destroy(); } catch( Middsol.CORBA.UserException exUser) { Console.WriteLine("CORBA-UserException\n {0}", exUser.GetType().ToString()); } catch( Middsol.CORBA.SystemException exSys) { Console.WriteLine("CORBA-SystemException\n {0}", exSys.ID); } Bring up the Greetings Object public class GreetingsImpl: Valtype.GreetingsPOA { public override Valtype.Info hello( Valtype.Info theInfo ) { System.Console.WriteLine("\nhello called with\n {0}", theInfo.toString()); Valtype.InfoDefaultFactory oFactory = new Valtype.InfoDefaultFactory(); Valtype.Info oInfo = oFactory.create( "Jack", "The weather will be bad!" ); System.Console.WriteLine("\nReturning\n {0}", oInfo.toString()); return oInfo; } The “hello” method implementation Implicit unmarshalling – ready to use Make a new Info object (you do not have to use the factory)

14. Sun ORB Java Mapping Interface / classDescription public abstract class Info implements org.omg.CORBA.portable.StreamableValue Generated – an abstract class. This is the one we need to implement abstract public class InfoHelperGenerated – the Helper class. Contains utility code. public final class InfoHolder implements org.omg.CORBA.portable.Streamable Generated – the Holder class public interface InfoValueFactory extends org.omg.CORBA.portable.ValueFactory Generated – an interface for the factory public class InfoDefaultFactory implements InfoValueFactory Generated – a “default” factory, so that we need not bother do it ourselves Also generated: all classes / interfaces for the Greetings interface – but this will not be mentioned here SUN Java ORB Generates: -All needed functionality for marshalling / unmarshalling -An abstract Info class (so the same as Middcor + Holder) -We still need to implement the InfoImpl class

15. public class InfoImpl extends Info { public InfoImpl() { } public InfoImpl( String name, String message ) { _name = name; _message = message; } public String _toString() { return "Name: "+_name+" Message: "+_message; }; } You may add all the methods you like – if you need them locally. These may differ on server & client. Constructors are nessecary for the factory Java InfoImpl Implementation Only _toString() needs to be overridden as this was the only abstract method Maybe you want getter and setter methods?

16. The Java Client public static void main(String args[]) { try{ // create and initialize the ORB org.omg.CORBA.ORB orb = org.omg.CORBA.ORB.init(args, null); // Get the stringified object reference and destringify it. java.io.BufferedReader in = new java.io.BufferedReader(new java.io.FileReader("c:\\Valuetype.ior")); String ref = in.readLine(); org.omg.CORBA.Object obj = orb.string_to_object(ref) ; Greetings oGreetings = GreetingsHelper.narrow(obj); // Create parameter for the server InfoImpl oInfo = new InfoImpl("Stefan", "Another Hello World Call"); // call the Greetings server object and print results Info oRetInfo = oGreetings.hello( oInfo ); System.out.println(oRetInfo._toString()); } catch (Exception e) { System.out.println("ERROR : " + e) ; e.printStackTrace(System.out); } Seems familiar?

17. Orbacus ORB C++ Interface / classDescription class Info : virtual public ::CORBA::ValueBaseGenerated – abstract Info class typedef OB::ObjVar Info_varGenerated Info_var type for easy memory management class Info_init : public ::CORBA::ValueFactoryBaseGenerated – abstract ValueFactoryBase Also generated: all classes for the Greetings interface – but this will not be mentioned here Orbacus ORB - We need to implement both Info object and the factory

18. Other Valuetype possibilites There are other valuetypes which we shall not discuss here (not part of curriculum) Abstract value May be used for polymorphic reasons Abstract interface May be used for polymorphic reasons for determining the interface at runtime Pass by reference semantics of operations attributes are transferred by value operations ”supports” by reference Use the ”supports” keyword Results is rather non-transparent semantics

19. Remember Valuetypes are for implementing the DTO / replicating objects pattern to avoid the round-trip anti-pattern AND reduce the number of CORBA objects running at server But it is also just a convenient way of moving data in general between all layers Sometimes you may just want to use “structs” – and maybe map these to objects at the receiving side Check your ORB vendor for compliance – and generation support

20. Group Work When using OR-mappers: EJB, JPA, Hibernate, NHibernate, LLBLGen, or DB4O as the Persistency Layer Discuss (10 minutes): Which design implications will it have whether you select structs or valuetypes for DTO/replicating objects pattern? Which potential challenges do you see with regards to mapping valuetypes and OR-mapper object types Would RDBMS/SQL be better suited? Plenum (5 minutes): Let’s discuss your results

21. Læringsmål Alignment Når kurset er færdigt forventes den studerende at kunne: Definere, beskrive og sammenligne forskellige typer af objektorienterede middleware frameworks til apparater og computere, med primær fokus på CORBA og sekundært.NET Remoting teknologierne, herunder fordele og ulemper forbundet med de forskellige teknologier Definere og beskrive principper omkring transparens og heterogenitet i relation til middlewareteknologier Definere og beskrive gængse teorier, metoder og retningslinier indenfor det objektorienterede middleware paradigme og anvende disse til at designe effektive distribuerede systemer Designe og konstruere et distribueret system der gør brug af CORBA og.NET Remoting teknologierne med tilhørende værktøjssupport CORBA valuetypes er et væsentligt element i CORBA’s arkitektur. mange andre teknologier er Dog bedre end CORBA her CORBA valuetypes er et væsentligt element i CORBA’s arkitektur. mange andre teknologier er Dog bedre end CORBA her MANGLER: hvordan I praktisk omsætter denne viden. Fås ved øvelse og projekt. Valuetypes er vigtige for Access Transperency og heterogenitet Valuetypes er vigtige for Access Transperency og heterogenitet Meget væsentligt arkitektur Aspekt at berherske Valuetypes og forskellene Med andre komplekse typer Meget væsentligt arkitektur Aspekt at berherske Valuetypes og forskellene Med andre komplekse typer