Notes

Outline

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)

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

The Naming Service (interfaces) org.omg.CosNaming: NamingContext: primary interface to naming service NameComponent: identify (name/kind) services BindingInterator: 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

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()

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()

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);

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;

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 + "/");   }  }

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

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)

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

Registering Services Example: NameClient.java This will add names to the namespace: Plans is an object reference Personal is a naming context that contains two object references: Calendar and Schedule

Clearing the Naming Service Steps: Get a reference to initial naming context Recursively iterate through the sub naming contexts Call unbind Call destroy

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)

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 }

Advanced IDL: Sequences A sequence is a 1-D array that can be of variable size Two types: Bounded sequences         sequence<long, 15>employee; Unbounded sequences      sequence<long> employee

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); };

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 vindl CReditCard visa, amex, discover;     public static final int _visa, _amex, _discover;     public int value(); } To compare (using switch): (unknown.value() == _visa)

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; };

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); }

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)

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”; };