1. Copyright (c) Qusay H. Mahmoud 1 The Naming Service (Client’s View) A tree-like directory for object references Much like a file system: provides directory structure for files Object references are stored by name Each object reference-name pair is called a name binding Name bindings may be organized under naming contexts (name binding itself) All bindings are stored under initial naming context (the only persistent binding)

2. Copyright (c) Qusay H. Mahmoud 2 The Naming Service…. Your client’s ORB must know the name and port# of a host running the naming service The naming service can either be the JavaIDL naming service or any COS-compliant service To start: tnameserv –ORBInitialPort port# – The default port number is 900 To stop: use relevant OS command (kill, ctrl-c) Namespace is lost if name server halts/restarts

3. Copyright (c) Qusay H. Mahmoud 3 The Naming Service (interfaces) org.omg.CosNaming: – NamingContext: primary interface to naming service – NameComponent: identify (name/kind) services – BindingIterator: iterating through the contents – Binding: a single entry in the naming service – BindingList: a list of entries in the naming service – BindingType: the type of an entry

4. Copyright (c) Qusay H. Mahmoud 4 Naming Service (NamingContext) Analogous to a directory on a file system Contains a series of named objects An object in a NamingContext may be another NamingContext (analogous to subdirectory) A reference to the top level NamingContext can be obtained with the ORB method: resolve_initial_references()

5. Copyright (c) Qusay H. Mahmoud 5 Naming Service (NamingContext) To get a reference to an object stored under NamingContext, use: resolve(NameComponent namePath) It throws: NotFound, CannotProceed, InvalidName This method returns org.omg.CORBA.Object Therefore, it must be narrowed to a particular interface using a helper’s narrow()

6. Copyright (c) Qusay H. Mahmoud 6 Browsing the Naming Service The top level only…. import org.omg.CORBA.*; import org.omg.CosNaming.*; public class Browser { ORB orb = ORB.init (args, null); // obtain a reference to the naming service org.omg.CORBA.Object nc = orb.resolve_initial_references ("NameService"); NamingContext namingContext = NamingContextHelper.narrow (nc);

7. Copyright (c) Qusay H. Mahmoud 7 Browsing the Naming Service…. BindingListHolder b1 = new BindingListHolder (); BindingIteratorHolder b2 = new BindingIteratorHolder (); // get initial content-list namingContext.list (10, b1, b2); // print out bindings Binding[] bindings = b1.value; if(bindings.length == 0) return;

8. Copyright (c) Qusay H. Mahmoud 8 Browsing the Naming Service…. for (int i = 0; i < bindings.length; i++) { Binding binding = bindings[i]; NameComponent[] name = binding.binding_name; BindingType type = binding.binding_type; if (type == BindingType.nobject) { System.out.println (name[0].id + "-" + name[0].kind); } else { // BindingType.ncontext System.out.println (name[0].id + "-" + name[0].kind + "/"); }

9. Copyright (c) Qusay H. Mahmoud 9 CORBA Servers Implement the IDL interfaces by subclassing the appropriate pregenerated skeleton class Each class is called a servant The HelloServer Example (Slide 34) – Initialize the ORB – Create initial objects (servants) – Connect each servant to the ORB – Bind the servants in the naming service – Wait for connections

10. Copyright (c) Qusay H. Mahmoud 10 CORBA Servers (ObjectImpl) When a servant extends the _interfaceObjectImpl, it is actually extending the orb.omg.CORBA.Portable.ObjectImpl class This class provides a variety of helper methods (including all methods of CORBA Object)

11. Copyright (c) Qusay H. Mahmoud 11 Naming Service (Server’s View) Registering/Unregistering services: bind: register the object under the specified name rebind:identical to bind(), but an AlreadyBound exception won’t be thrown – existing object replaced unbind:unregister a CORBA object Creating new naming contexts: bind_new_context, new_context, bind_context Destroying a naming context: destroy: destroy an empty NamingContext

12. Copyright (c) Qusay H. Mahmoud 12 Clearing the Naming Service Steps: – Get a reference to initial naming context – Recursively iterate through the sub naming contexts – Call unbind – Call destroy

13. Copyright (c) Qusay H. Mahmoud 13 Advanced IDL IDL supports C/C++ style comments: // This is a comment /* This is another comment */ Also, it supports: – conditionals (#if) – defines (#define) – includes (#include) idlj requires access to a C preprocessor (cpp)

14. Copyright (c) Qusay H. Mahmoud 14 Advanced IDL: Arrays IDL provides multidimensional fixed-size arrays The array size is fixed at compile time IDL arrays map directly into Java arrays Example: interface Customer { attribute string address[4]; // 1-D array attribute short table[5][7]; // 2-D array }

15. Copyright (c) Qusay H. Mahmoud 15 Advanced IDL: Sequences A sequence is a 1-D array that can be of variable size Two types: – Bounded sequences sequence employee; – Unbounded sequences sequence employee

16. Copyright (c) Qusay H. Mahmoud 16 Advanced IDL: Enumerations The enum data type defines an enumeration – A user-defined data type that can hold one of a fixed set of values Example: enum CreditCard { visa, amex, discover }; interface Bank { void applyForCreditCard(CreditCard cc); };

17. Copyright (c) Qusay H. Mahmoud 17 Enumerations (mapping to Java) An enum is mapped to a Java class with static variables representing the set of values Example: public class CreditCard { public static final CreditCard visa, amex, discover; public static final int _visa, _amex, _discover; public int value(); } To compare (using switch): (unknown.value() == _visa)

18. Copyright (c) Qusay H. Mahmoud 18 Advanced IDL: Structures The IDL type struct defines a structure Use a struct to group related data together Example: struct Name { string firstName; string lastName; }; interface Customer { attribute Name name; };

19. Copyright (c) Qusay H. Mahmoud 19 Structures (mapping to Java) A struct is mapped to a Java class that provides instance variables for the fields, and a constructor for all values, and a null constructor Example: public class Name { public String firstName; public String lastname; public Name(); public Name(String firstName, String lastName); }

20. Copyright (c) Qusay H. Mahmoud 20 Advanced IDL: typedefs A typedef is an alias, or another name for an existing data type Example: typedef long age; interface Customer { age howOld; } Typedefs of simple data types are mapped to the original (I.e. replaced by the more basic type)

21. Copyright (c) Qusay H. Mahmoud 21 Advanced IDL: Constants 1. Within an interface: interface Foo { const long aLong = -32; }; Mapped to: public interface Foo { public static final int aLong = (int) –32L; }; 2. Not within an interface: const string Message=“hello”; Mapped to: public interface Message { public static final String Message=“hello”; };