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

Copyright (c) Qusay H. Mahmoud1

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 namerebind:identical to bind(), but an AlreadyBound

exception won’t be thrown – existing object replacedunbind: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”; };

Documents

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