ABSTRACT

This Netscape TechNote will explore the Naming Service provided with Netscape ISB, the ORB shipped with Enterprise Server 3.x and Communicator 4.x.  We will demonstrate how to use the Naming Service to bind and resolve CORBA object references using Java, JavaScript, and C++.  Please note that an application may be both a client (user of a CORBA Object) and a server (a CORBA Object).

• Introduction
• What is WAI?
• Where is OSAgent?
• Pre-Requisites
• To use CORBA and the Naming Service
• To develop and run Java/C/C++ applications using Enterprise Server's ORB
• To develop Java applications and applets using Communicator's ORB
• To run Java applications and applets using Communicator's ORB
• To use CORBA and the Naming Service from Server-Side JavaScript
• To use CORBA and the Naming Service from a separate machine
• Naming Service APIs
• Accessing using Java: Application
• Accessing using Java: Applet
• Accessing using C++
• Accessing using Client-Side JavaScript
• Accessing using Server-Side JavaScript
• Accessing using Visual JavaScript
• Using NamingContext

Naming Service is a CORBAservice that allows components on the object bus to locate other components on the object bus by a user definable name.  Netscape Enterprise Web servers and Netscape Communicator contain methods that allow you to access the naming services built into the web server. These naming services allow you to associate a URL with an object. Once the URL is associated with the object, any client of the web server can access the object reference through the URL.

One big difference is that for Java register and resolve calls the behavior in the Enterprise Server's ORB libraries are different from the Communicator's ORB libraries.  Communicator ORB's register/resolve internally uses the HTTP PUT/GET methods to place the reference to the CORBA object on  a web server.  Enterprise Server ORB's register/resolve internally uses CosNaming to access the Naming Service.  Note that the register call from the Communicator's ORB can be used to placed the IOR on any web server that allows web publishing.  And the resolve call from the Communicator's ORB can be used to get an IOR from any web server.  See the Naming Service APIs for the exact differences.

The registerObject call is more tied to the Enterprise Server.  Since it uses the Enterprise Server's naming service directly by using CosNaming and will only work if
you are using Enterprise Server as the Web Server.

I've been using registerObject when using the Enterprise Server's ORB and register when I use the Communicator's ORB (NameUtil class is not available with the
Communicator's ORB).

Here's the general mapping for registering and resolving.  See the Naming Service APIs for the exact mapping details.

CORBA Objects should always be mapped under the path /NameService.

http://<hostAndPort>/NameService/<object_name>
OR

http://<hostAndPort>/NameService/WAS/<object_name>

Please see the WAI documentation for more information on the Naming Service.
 

WAI, Web Application Interface, is the API to extend Enterprise Server functionality.  WAS, Web Application Service, is the application that is written using WAI.  Enterprise Server 3.0x and later will use WAI as the primary API to extend server functionality.  Please see WAI documentation for more details.

Q. Why is WAI mentioned in a CORBA TechNote?
A. WAI is implemented using CORBA.  Hence, the pre-requisites and documentation for setting up CORBA and WAI overlap.

OSAgent is the Naming Service provided by Visigenic VisiBroker.  With Enterprise Server 3.0, OSAgent can be used as the Naming Service.  However from Enterprise Server 3.0c + WAI Patch and later, OSAgent is no longer supported.  The Naming Service APIs described in this TechNote should be used instead.

Q. OSAgent was so easy to use, why did Netscape take it out of Enterprise Server?
A. The use of OSAgent by-passed the security model provided by the web server.  Removal of OSAgent allows the Enterprise Server's Naming Service to utilize the security features provided by Enterprise Server.  In this way, the Naming Service becomes just another web resource that can be control by Enterprise Server's Access Control Lists.

• Enable CORBA on Enterprise Server
• For more details on customizing the ORB, see the WAI documentation, specifically Setting Up the Web Server.

• For Java: Set CLASSPATH to include <server_root>/wai/java/nisb.zip;<server_root>/wai/java/WAI.zip
• For Java/C/C++ see the WAI documentation, specifically Using WAI.

• Set CLASSPATH to include <comm_root>/Program/Java/Classes/java40.jar;<comm_root>/Program/Java/Classes/iiop10.jar

• Application: Set CLASSPATH to include <comm_root>/Program/Java/Classes/java40.jar;<comm_root>/Program/Java/Classes/iiop10.jar
• Applet: No special settings necessary.

• Read the security guidelines.  See the WAI documentation, specifically Security Guidelines for Using WAI.
• Set the access control lists to allow for writing from a separate machine.  See Configuring Web Naming Security in the Enable CORBA on Enterprise Server TechNote.

There are three types of APIs: Registering, Resolving, and Utilities.  Registering associates a CORBA Object with a URL.  Resolving converts a URL into a CORBA object reference.  Utilities are APIs that allow you to access CosNaming interfaces.  Different ways of registering and resolving are inter operable. 

Enterprise Server's Naming Service APIs^*

Communicator's Naming Service APIs

Enterprise Server : C++ : registerObject

DESCRIPTION:

Registers a CORBA Object to a URL.

MAPPING: A C++ registerObject call maps the obj's reference to:

http://<hostAndPort>/NameService/<objectName>

EXAMPLE:

ret = registerObject( "mikelee:80", "Howdy", obj );
 
maps the obj to
 
http://mikelee:80/NameService/Howdy

Enterprise Server : C++ : registerWAS

DESCRIPTION:

Registers a CORBA Object to a URL.

MAPPING: A C++ registerWAS call maps the obj's reference to:

http://<hostAndPort>/NameService/WAS/<objectName>

EXAMPLE:

rc = registerWAS("mikelee:80", "Howdy", obj);
 
maps the obj to
 
http://mikelee:80/NameService/WAS/Howdy

Enterprise Server : C++ : resolveURI

DESCRIPTION:

Registers a CORBA Object to a URL.

MAPPING:  A C++ resolveURI call maps the obj's reference to:

http://<host>:<port>/<uri>

EXAMPLE:

rc = resolveURI("mikelee", 80, "/NameService/Howdy", obj);
 
resolves using
 
http://mikelee:80/NameService/Howdy

Enterprise Server : C++ : resolveWAS

DESCRIPTION:

Registers a CORBA Object to a URL.  This call automatically looks up the host.

MAPPING:  A C++ resolveWAS call maps the obj's reference to:

http://<host>/NameService/WAS/<objectName>

EXAMPLE:

obj = resolveWAS("Howdy");
 
resolves using
 
http://mikelee:80/NameService/WAS/Howdy

Enterprise Server : Java : register

DESCRIPTION:

Registers a CORBA Object to a URL.  This call automatically inserts "NameService" in between the host and the path/object name.  Calling register using the Enterprise Server's ORB is different than using Communicator's ORB.

MAPPING:  A Java register call using Enterprise Server's ORB maps the obj's reference to:

http://<modified url>

EXAMPLE:

obj = register("http://mikelee:80/Howdy");
 
maps obj to
 
http://mikelee:80/NameService/Howdy

Communicator : Java : register

DESCRIPTION:

Registers a CORBA Object to a URL.  This call uses an HTTP Put command to place the CORBA Object's reference at the specified URL.  Calling register using the Communicator's ORB is different than using Enterprise Server's ORB.

MAPPING:  A Java register call using Communicator's ORB maps the obj's reference to:

http://<url>

EXAMPLE:

obj = register("http://mikelee:80/NameService/Howdy");
 
maps obj to
 
http://mikelee:80/NameService/Howdy
 

Enterprise Server : Java : registerObject

DESCRIPTION:

Registers a CORBA Object to a URL.  Unlike the C++ call, "NameService" has to be manually inserted within the uri.

MAPPING:  A Java registerObject call maps the obj's reference to:

http://<hostAndPort>/<uri>

EXAMPLE:

obj = registerObject("mikelee:80", "/NameService/Howdy", obj);
 
maps obj to
 
http://mikelee:80/NameService/Howdy

Enterprise Server : Java : registerWAS

DESCRIPTION:

Registers a CORBA Object to a URL.

MAPPING:  A Java registerWAS call maps the obj's reference to:

http://<hostAndPort>/NameService/WAS/<objectName>

EXAMPLE:

obj = registerWAS("mikelee:80", "Howdy", obj);
 
maps obj to
 
http://mikelee:80/NameService/WAS/Howdy

Enterprise Server : Java : resolve

DESCRIPTION:

Resolves a CORBA Object reference from a URL.  This call automatically inserts "NameService" in between the host and the path/object name.  Calling resolve using the Enterprise Server's ORB is different than using Communicator's ORB.

MAPPING:  A Java resolve call maps the obj's reference to:

http://<modified url>

EXAMPLE:

obj = resolve("http://mikelee:80/Howdy");
 
resolves using
 
http://mikelee:80/NameService/Howdy

Communicator : Java : resolve

DESCRIPTION: Registers a CORBA Object to a URL.  Calling register using the Communicator's ORB is different than using Enterprise Server's ORB.
MAPPING:  A Java resolve call using Communicator's ORB maps the obj's reference to:

http://<url>

EXAMPLE:

obj = resolve("http://mikelee:80/NameService/Howdy");
 
resolves using
 
http://mikelee:80/NameService/Howdy

Enterprise Server : Java : resolveURI

DESCRIPTION:

Registers a CORBA Object to a URL.

MAPPING: A Java resolveURI call maps the obj's reference to:

<protocol>://<host>:<port>/<uri>

EXAMPLE 1:

obj = resolveURI("http", "mikelee", 80, "/NameService/Howdy");
 
resolves using
 
http://mikelee:80/NameService/Howdy

EXAMPLE 2:

obj = resolveURI("http", "mikelee", 80, "/NameService/WAS/Howdy");
 
resolves using
 
http://mikelee:80/NameService/WAS/Howdy

Enterprise Server : Java : getRootNaming

DESCRIPTION:

Gives access to CosNaming by returning a NamingContext.  See Using NamingContext for more details.

Enterprise Server : Java : NameFromString

DESCRIPTION:

Converts a string to CosNaming.NameHolder (NameHolder is equivalent to Name in CosNaming).  See Using NamingContext for more details.

DESCRIPTION:

A Java application that is run outside of the browser may use either the Communicator's ORB or the Enterprise Server's ORB.

Communicator ORB:

register
resolve

Enterprise Server ORB:

register/registerObject/registerWAS
resolve/resolveURI

MORE INFO:

• Writing Web Applications with WAI
• Netscape ISB for Java Programmer's Guide
• Netscape ISB for Java Reference Guide

PRE-REQ:

Communicator ORB:
Developing: Setup CLASSPATH
Running: Setup CLASSPATH

Enterprise Server ORB:

Developing and Running: Setup CLASSPATH

EXAMPLE 1: Registering using Enterprise Server's ORB

package SendMsg;

public class MsgService {
  static public void main( String[] args ) {
    //Instantiate Corba Implementation
    try {
        // Initialize ORB
        org.omg.CORBA.ORB orb= org.omg.CORBA.ORB.init();

        // Initialize BOA
        org.omg.CORBA.BOA boa = orb.BOA_init();

        // Create CORBA Object
        HelloImpl hi = new HelloImpl( "Howdy" );

        // Export newly created object to the ORB
        boa.obj_is_ready( hi );

        // Register object using web naming
        // Alternatively:
        //   netscape.WAI.Naming.register( "http://mikelee:80/Howdy", hi );
        // May be used.
        netscape.WAI.NameUtil.registerObject( "mikelee:80", "/NameService/Howdy", hi );
        System.out.println("Howdy: Ready for Service");
 
        boa.impl_is_ready( );
    }
    catch ( Exception e ) {
        System.err.println(e);
        e.printStackTrace();
    }
  }
}

EXAMPLE 2:  Resolving using Enterprise Server's ORB

package SendMsg;

public class MsgClient {
  static public void main( String[] args ) {
    //Instantiate Corba Implementation
    try {
      // Initialize ORB
      org.omg.CORBA.ORB orb= org.omg.CORBA.ORB.init();

      String protocol = "http";
      String host = "mikelee";
      int port = 80;
      String uri = "/NameService/Howdy";
      // Resolve object
      // Alternatively:
      //   netscape.WAI.Naming.resolve( "http://mikelee:80/Howdy" );
      // May be used.
      org.omg.CORBA.Object o = netscape.WAI.NameUtil.resolveURI( protocol, host, port, uri );
      Hello hi = HelloHelper.narrow(o);
      System.out.println(hi.sayHello());
    }
    catch ( Exception e ) {
      System.err.println(e);
      e.printStackTrace();
    }
  }
}

EXAMPLE 3: Registering using Communicator's ORB

package SendMsg;

public class MsgService {
  static public void main( String[] args ) {
    //Instantiate Corba Implementation
    try {
        // Initialize ORB
        org.omg.CORBA.ORB orb= org.omg.CORBA.ORB.init();

        // Initialize BOA
        org.omg.CORBA.BOA boa = orb.BOA_init();

        // Create CORBA Object
        HelloImpl hi = new HelloImpl( "Howdy" );

        // Export newly created object to the ORB
        boa.obj_is_ready( hi );

        // Register object using web naming
        String url = "http://mikelee/NameService/Howdy";
        netscape.WAI.Naming.register( url, hi );
        System.out.println(url + ": Ready for Service");
 
        boa.impl_is_ready( );
    }
    catch ( Exception e ) {
        System.err.println(e);
        e.printStackTrace();
    }
  }
}

EXAMPLE 4:  Resolving using Communicator's ORB

package SendMsg;

public class MsgClient {
  static public void main( String[] args ) {
    //Instantiate Corba Implementation
    try {
      // Initialize ORB
      org.omg.CORBA.ORB orb= org.omg.CORBA.ORB.init();

      String url = "http://mikelee/NameService/Howdy";
      // Resolve object
      org.omg.CORBA.Object o =netscape.WAI.Naming.resolve( url );
      Hello hi = HelloHelper.narrow(o);
      System.out.println(hi.sayHello());
    }
    catch ( Exception e ) {
      System.err.println(e);
      e.printStackTrace();
    }
  }
}

DESCRIPTION:

Java applets uses the Naming Service APIs for Communicator's ORB.
Note: The applet security model applies.

MORE INFO:

• Writing Web Applications with WAI
• Netscape ISB for Java Programmer's Guide
• Netscape ISB for Java Reference Guide

PRE-REQ:

• Developing: Setup CLASSPATH
• Running: Setup CLASSPATH

EXAMPLE:  Registering

package SendMsg;
import java.applet.*;

public class MsgClientApplet extends Applet {
  public void init( ) {
    //Instantiate Corba Implementation
    try {
      // Initialize ORB
      org.omg.CORBA.ORB orb= org.omg.CORBA.ORB.init();

      // Initialize BOA
      org.omg.CORBA.BOA boa = orb.BOA_init();

      // Create Hello Implementation Object
      HelloImpl hi = new HelloImpl( "Mike" );

      // Export newly created object to the ORB
      boa.obj_is_ready( hi );

      // Register object using web naming
      String url = "http://" + getCodeBase().getHost()
                 + ":" + getCodeBase().getPort()
                 + "/NameService/Howdy";
      netscape.WAI.Naming.register( url, hi );
      System.out.println( url + ": Ready for Service");
 
      boa.impl_is_ready( );
    }
    catch ( Exception e )
    {
      System.err.println(e);
      e.printStackTrace();
    }
  }
}

EXAMPLE: Resolving

package SendMsg;
import java.applet.*;

public class MsgClientApplet extends Applet{
  public void init( ) {
    //Instantiate Corba Implementation
    try {
        // Initialize ORB
        org.omg.CORBA.ORB orb= org.omg.CORBA.ORB.init();

        // Register object using web naming
        String url = "http://" + getCodeBase().getHost()
                 + ":" + getCodeBase().getPort()
                 + "/NameService/Howdy";
        org.omg.CORBA.Object o = netscape.WAI.Naming.resolve( url );
        Hello hi = HelloHelper.narrow(o);
        System.out.println(hi.sayHello());
    }
    catch ( Exception e ) {
        System.err.println(e);
        e.printStackTrace();
    }
  }
}

DESCRIPTION:

C++ applications can uses the Naming Service APIs for Enterprise Server's C++ ORB.

MORE INFO:

• Writing Web Applications with WAI
• Netscape ISB for C++ Reference Guide

PRE-REQ:

• Developing and Running

EXAMPLE: Registering

// MsgService.cpp
#include "HelloImpl.cpp"
#include <NameUtil.hpp>
int main(int argc, char* const* argv) {
  try{
    // Initialize the ORB and the BOA.
    CORBA::ORB_var orb = CORBA::ORB_init(argc, argv);
    CORBA::BOA_var boa = orb->BOA_init(argc, argv);
    HelloImpl* hi = new HelloImpl();
    WAIReturnType_t rc;
    char *objectName = "Howdy";
    char *hostAndPort = "mikelee:80";
    boa->obj_is_ready(hi);
    rc = registerObject(hostAndPort, objectName, hi);
    cerr << objectName << ": Ready for Service" << endl;
    boa->impl_is_ready();
    return(0);
  }
  catch (CORBA::SystemException& e)
  {
    cerr << e << endl;
    return(1);
  }
  catch (...)
  {
    cerr << "Unknown exception" << endl;
    return(1);
  }
  return(0);
}

EXAMPLE: Resolving

// MsgClient.cpp
#include "SendMsg_c.hpp"
#include <NameUtil.hpp>

int main(int argc, char* const* argv) {
  try {
    // Initialize the ORB.
    CORBA::ORB_ptr orb = CORBA::ORB_init(argc, argv);
    SendMsg::Hello_var hi;
    // Find a reference to the Hello service.
    WAIReturnType_t ret;
    CORBA::Object_ptr p;
    char* host = "mikelee";
    int port = 80;
    char* objName = "/NameService/Howdy";
    ret = resolveURI(host, port, objName, p);
    // Narrow the reference.
    hi = SendMsg::Hello::_narrow(p);
    // Call a method provided by the service.
    cout << hi->sayHello() << endl;
  }
  catch (CORBA::SystemException& e)
  {
    cerr << e << endl;
    return(1);
  }
  catch (...)
  {
    cerr << "Unknown exception" << endl;
    return(1);
  }
  return(0);
}

DESCRIPTION:

CSJS (Client-Side JavaScript) uses the Naming Service APIs for Communicator's ORB.  CORBA Objects should be registered from outside of CSJS.

PRE-REQ:

None

EXAMPLE: Resolving

<SCRIPT>
  // Initialize ORB
  var orb = Packages.org.omg.CORBA.ORB.init();
  var url = "http://mikelee/NameService/Howdy";
  var o = Packages.netscape.WAI.Naming.resolve( url );
  var hi = Packages.SendMsg.HelloHelper.narrow( o );
  var str = hi.sayHello();
  document.write( "<H1> + str + "</H1>");
</SCRIPT>

DESCRIPTION:

SSJS (Server-Side JavaScript) uses the Naming Service APIs for Enterprise Server's Java ORB.  However, the resolve call does not work with SSJS, resolveURI should be used instead.  CORBA Objects should be registered from outside of CSJS or SSJS (Server-Side JavaScript).

Note: The Flexi example mentioned in Working with Java and CORBA Objects Through LiveConnect is incorrect.  Should be using resolveURI instead of resolve.

MORE INFO:

• TechNote: Basic Server-Side JavaScript
• Documentation: Writing Server-Side JavaScript, specifically Working with Java and CORBA Objects Through LiveConnect

PRE-REQ:

• Developing and Running using Enterprise Server Java ORB
• Working with Java and CORBA Objects Through LiveConnect

EXAMPLE: Resolving

<SERVER>
  // No need to initialize the orb. ORB already initialized by Enterprise Server.

  // By default, assume name service is running on this server.
  var protocol = "http";
  var host = server.hostname;
  var port = 80;
  var uri = "/NameService/Howdy";
  var o = netscape.WAI.NameUtil.resolveURI("http", "mikelee", 80, "/NameService/Howdy");
  project.hi = Packages.SendMsg.HelloHelper.narrow(o);
  var str = project.hello.sayHello();
  write( "<H1>" + str + "</H1>" );
</SERVER>

This topic is covered by Visual JavaScript Developer's Guide and the Component Developer's Guide.  Specifically, see Component Developer's Guide's chapter on Using CORBA Components.  Visual JavaScript uses the client URL mapping of the Communicator's Naming APIs.

NamingContext allows access to CosNaming.  A detailed discussion of NamingContext is out of scope for this TechNote.  For detailed information please see the book by Andreas Vogel and Keith Duddy, Java Programming with CORBA.

Q. Why mention NamingContext at all?
A. NamingContext allows you to get full access to CosNaming.  However for this TechNote we will focus on the functionality that allows you to know if a CORBA server is:

• not registered (not started)
• started but not responding

Currently when you start a CORBA Object, let's call it "Howdy," and register it with the Naming Service, this rebinds the Object reference with the url.  Even if we stop the server, the Naming Service still has "Howdy" registered.  When a client attempts to access "Howdy" the exception that is thrown merely states that the connection was refused because of org.omg.CORBA.COMM_FAILURE.  The client has no idea if the server was stopped or there was an error condition within the network.

To address this, we can "unbind" a CORBA server during it's shutdown.  If we unbind "Howdy" during shutdown of the "Howdy" server, we can catch the following exceptions attempting to access the "Howdy" server:

• org.omg.CORBA.INV_OBJREF:  Server not registered (not started) at the requested URL:
• org.omg.CORBA.COMM_FAILURE:  Server registered, but some other error condition (server crashed, etc):

EXAMPLE 1: Shutdown

...
// "Howdy" already registered within the Naming Service
public void shutdown {
  //Instantiate Corba Implementation
  try {
    // Assumption: ORB already initialize ORB
 
    // Retrieve NamingContext of web server
    CosNaming.NamingContext nc = netscape.WAI.NameUtil.getRootNaming("mikelee", 80);

    // Create NameHolder with "Howdy
    CosNaming.NameComponent[] howdyName;
    howdyName = NameUtil.NameFromString("Howdy", "/").value;

        // Unregister "Howdy" from NameService
    nc.unbind( howdyName );
  catch ( Exception e ) {
        System.err.println(e);
        e.printStackTrace();
  }
}
...

EXAMPLE 2: Resolving, with more granular exception handling.

package SendMsg;

public class MsgClient {
  static public void main( String[] args ) {
    //Instantiate Corba Implementation
    try {
        // Initialize ORB
        org.omg.CORBA.ORB orb= org.omg.CORBA.ORB.init();

        // Register object using web naming
        org.omg.CORBA.Object o = netscape.WAI.Naming.resolve( "http://mikelee/Howdy" );
        Hello hi = (Hello)HelloHelper.narrow(o);
        System.out.println(hi.sayHello());
    }
    catch ( org.omg.CORBA.INV_OBJREF e ) {
        System.err.println("Server not started");
        System.err.println(e);
        e.printStackTrace();
    }
    catch ( org.omg.CORBA.COMM_FAILURE e ) {
        System.err.println("Cannot reach server.  Server went down or communication failure.");
        System.err.println(e);
        e.printStackTrace();
    }
    catch ( Exception e ) {
        System.err.println("Unknown exception.");
        System.err.println(e);
        e.printStackTrace();
    }
  }
}
 

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