netscape.WAI.Naming class. This class is part of the nisb.zip file in the Netscape Enterprise Server and the iiop10.jar file in Netscape Communicator. The methods behave slightly differently depending on which ORB is used. Differences are described below.
http://host[:port]/path/name. The caller's machine must be allowed to do an HTTP 'PUT' on the designated host.
Calling register using the Enterprise Server's ORB is different than calling register using the Communicator's ORB. With the Enterprise Server, this call automatically prepends NameService/ to the specified path/name. For example:
register("http://mikelee/HelloService", service);
registers the object with the following (automatically modified) URL:
http://mikelee/NameService/HelloServiceWith the Communicator, the URL is not automatically modified, so you need to specify the
NameService/ prefix yourself. For example:
register("http://mikelee/NameService/HelloService", service);
If the object has already been registered with a URL, this method replaces (overwrites) the old URL with a new one.
http://host[:port]/path/name.
Calling resolve using the Enterprise Server's ORB is different than calling resolve using the Communicator's ORB. With the Enterprise Server, this call automatically prepends NameService/ to the specified path/name. For example:
obj = resolve("http://mikelee/HelloService");
resolves a CORBA object using the following (automatically modified) URL:
http://mikelee/NameService/HelloServiceWith the Communicator, the URL is not automatically modified, so you need to specify the
NameService/ prefix yourself. For example:
obj = resolve("http://mikelee/NameService/HelloService");
The following code examples show how these methods are used by clients and services. The first example is part of a service application that calls register to register a service with the Enterprise Server's ORB.
// Part of a service application using the Enterprise Server's ORB.Following is part of a client applet that calls resolve to find a service, given a URL. Applets always use the Communicator's ORB.
public class HelloService extends _sk_HelloWorld {
public static void main(String args[]) {
// Initialize the BOA because we are going to accept connections.
BOA boa = orb.BOA_init();
/* Create the service. */
HelloService service = new HelloService();
/* Expose the service to the net. */
boa.obj_is_ready(service);
/* Register the service. */
try {
String host =
java.net.InetAddress.getLocalHost().getHostName();
Naming.register("http://" + host + "/HelloService", service);
// For the Communicator's ORB this call would be:
// Naming.register("http://" + host +
// "/NameService/HelloService", service);
} catch (Exception e)
{ e.printStackTrace();
System.exit( -1 );
}
/* Wait for requests. */
boa.impl_is_ready();
}
}
// Part of a client applet using the Communicator's ORB.
public class HelloClientApplet extends java.applet.Applet {
org.omg.CORBA.ORB orb;
HelloWorld hello;
public void init() {
/* Initialize the ORB. */
orb = org.omg.CORBA.ORB.init();
/* Resolve an object. */
// String host = getCodeBase().getHost();
String host = "myServer.nscp.com";
// From applets you can only use the Communicator's ORB.
String url_string = "http://" + host +
"/NameService/HelloService";
org.omg.CORBA.Object obj = Naming.resolve(url_string);
/* In some cases (where multiple CORBA interfaces
are implemented), casting requires a query to the
remote host. So we call 'narrow' to cast here. */
hello = HelloWorldHelper.narrow(obj);
if(hello == null)
unableToLocate(url_string); // bad cast returns null
setLayout(new GridLayout(1,1));
Button b = new Button("GO!");
add(b);
}
}
org.omg.CORBA.Object inherit methods that you can use to manipulate the object. Some of these methods are listed below; for a complete discussion of these and other methods, see the Netscape Internet Service Broker for Java Reference Guide.
NOTE:
You cannot use the instanceof keyword to determine the runtime type.
Table 3.1 From org.omg.CORBA.Object, methods on object references
Converting an Object Reference to a String
Object references are opaque and can vary from one ORB to another, so ISB for Java provides methods that allow you to convert an object reference to a string as well as convert a string back into an object reference. The CORBA specification refers to this process as "stringification."
| Method | Description |
|---|---|
| object_to_string | Converts an object reference to a string. |
| string_to_object | Converts a string back to an object reference. |
Narrowing Object References
The process of converting an object reference's type from a general super-type to a more specific sub-type is called narrowing.
NOTE: You cannot use the Java casting facilities for narrowing.ISB for Java maintains a typegraph for each object interface so that narrowing can be accomplished by using the object's narrow method. If the
narrow method determines it is not possible to narrow an object to the type you request, it will return NULL.
The narrow method generated for the AccountManager.
abstract public class AccountManagerHelper {
...
public static Bank.AccountManager narrow(org.omg.CORBA.Object object) {
...
}
...
}
module Bank {
interface Account {
float balance();
};
interface AccountManager {
Account open(in string name);
};
};
BOA.object_is_ready, the service's interface name is registered only if the object is named. Objects that are given an object name when they are created return persistent object references. See Object and Implementation Activation for a complete discussion of persistent and transient objects. To make a client use a specific service, provide an object name. Also, a client must specify object names to bind to more than one instance of a service at a time. The object name distinguishes between multiple instances of a service. If an object name is not specified, the ORB will return any suitable object with the specified interface.
Using Qualified Object Names with Servers
Consider a banking application where you need to have two AccountManager objects available; one for a bank in Chicago and one for another bank in Dallas. You may even want to implement two separate object servers, possibly on different hosts. Each server could instantiate its own AccountManager object, but each would use the AccountManager constructor that accepts an object name. The following code examples show the server code for creating AccountManagers named Dallas and Chicago, and the client code to connect to the Dallas AccountManager.
Creating AccountManagers with the object names Dallas and Chicago.
// Using Enterprise Server's ORB
A client binding to an AccountManager with the object name Dallas.
public class Server {
public static void main(String[] args) {
try {
// Initialize the ORB.
org.omg.CORBA.ORB orb = org.omg.CORBA.ORB.init();
// Initialize the BOA.
org.omg.CORBA.BOA boa = orb.BOA_init();
// Create the account manager objects.
AccountManager dalMngr= new AccountManager("Dallas"); AccountManager chiMngr= new AccountManager("Chicago"); // Export the newly created objects.
boa.obj_is_ready(dalMngr);
boa.obj_is_ready(chiMngr);
// Or, if using Communicator's ORB, the call would be:
// netscape.WAI.Naming.register
// ("http://myServer.nscp.com/NameService/Dallas", dalMngr);
netscape.WAI.Naming.register
("http://myServer.nscp.com/Dallas", dalMngr);
netscape.WAI.Naming.register
("http://myServer.nscp.com/Chicago", chiMngr);
// Optional status messages.
System.out.println(dalMngr + " is ready.");
System.out.println(chiMngr + " is ready.");
// Wait for incoming requests.
boa.impl_is_ready();
} catch (org.omg.CORBA.SystemException se) {
System.err.println(se);
}
}
}// Using Enterprise Server's ORB
public class Client {
public static void main(String args[]) {
try {
// Initialize the ORB.
org.omg.CORBA.ORB orb = org.omg.CORBA.ORB.init();
// Locate an account manager named Dallas.
// Or, if using Communicator's ORB, the urlStr should be:
// "http://myServer.nscp.com/NameService/Dallas";
String urlStr = "http://myServer.nscp.com/Dallas"); org.omg.CORBA.Object obj = netscape.WAI.Naming.resolve(urlStr); Bank.AccountManager manager = // Use args[0] as the account name, or a default.
Bank.AccountManagerHelper.narrow(obj);
String name = args.length > 0 ? args[0] : "Jack B. Quick";
// Request the account manager to open a named account.
Bank.Account account = manager.open(name);
// Get the balance of the account.
float balance = account.balance();
// Print out the balance.
System.out.println
("The balance in " + name + "'s account is $" + balance);
} catch (org.omg.CORBA.SystemException(se) {
System.err.println(se);
}
}
}
Last Updated: 02/04/98 13:46:50