Java IDL: Naming Service - JDK 5 Documentation v1.2.2, Java 2 SDK 英文文档

Naming Service

Topics in this section include:

• Java IDL Name Server
• Starting the Java IDL Name Server
• Stopping the Java IDL Name Server
• Sample Client: Adding Objects to the Namespace
• Sample Client: Browsing the Namespace

The CORBA COS (Common Object Services) Naming Service provides a tree-like directory for object references much like a filesystem provides a directory structure for files. The Naming Service provided with Java IDL is a simple implementation of the COS Naming Service specification.

Object references are stored in the namespace by name and each object reference-name pair is called a name binding. Name bindings may be organized under naming contexts. Naming contexts are themselves name bindings and serve the same organizational function as a file system subdirectory. All bindings are stored under the initial naming context. The initial naming context is the only persistent binding in the namespace; the rest of the namespace is lost if the Java IDL name server process halts and restarts.

For an applet or application to use COS naming, its ORB must know the name and port of a host running a naming service or have access to a stringified initial naming context for that name server. The naming service can either be the Java IDL name server or another COS-compliant name service.

Starting the Java IDL Name Server

You must start the Java IDL name server before an application or applet that uses its naming service. Installation of the Java IDL product creates a script (Solaris: tnameserv) or executable file (Windows NT: tnameserv.exe) that starts the Java IDL name server. Start the name server so it runs in the background.

If you do not specify otherwise, the Java IDL name server listens on port 900 for the bootstrap protocol used to implement the ORB resolve_initial_references() and list_initial_references() methods. Specify a different port, for example, 1050, as follows:

   tnameserv -ORBInitialPort 1050

Clients of the name server must be made aware of the new port number. Do this by setting the org.omg.CORBA.ORBInitialPort property to the new port number when creating the ORB object.

Stopping the Java IDL Name Server

To stop the Java IDL name server, use the relevant operating system command, such as kill. Note that names registered with the Java IDL name service disappear when the server is terminated.

Sample Client: Adding Objects to the Namespace

The following sample program illustrates how to add names to the namespace. It is a self-contained Name Server client that creates the following simple tree.

In this example, plans is an object reference and Personal is a naming context that contains two object references: calendar and schedule.

import java.util.Properties;
import org.omg.CORBA.*;
import org.omg.CosNaming.*;

public class NameClient
{
   public static void main(String args[])
   {
      try {

In the above section,

        Properties props = new Properties();
        props.put("org.omg.CORBA.ORBInitialPort", "1050");
        ORB orb = ORB.init(args, props);

 
        NamingContext ctx = NamingContextHelper.narrow(orb.resolve_initial_references("NameService"));
        NamingContext objref = ctx;

        NameComponent nc1 = new NameComponent("plans", "text");
        NameComponent[] name1 = {nc1};
        ctx.rebind(name1, objref);
        System.out.println("plans rebind sucessful!");

        NameComponent nc2 = new NameComponent("Personal", "directory");
        NameComponent[] name2 = {nc2};
        NamingContext ctx2 = ctx.bind_new_context(name2);
        System.out.println("new naming context added..");

        NameComponent nc3 = new NameComponent("schedule", "text");
        NameComponent[] name3 = {nc3};
        ctx2.rebind(name3, objref);
        System.out.println("schedule rebind sucessful!");

        NameComponent nc4 = new NameComponent("calender", "text");
        NameComponent[] name4 = {nc4};
        ctx2.rebind(name4, objref);
        System.out.println("calender rebind sucessful!");


    } catch (Exception e) {
        e.printStackTrace(System.err);
    }
  }  
}

import java.util.Properties;
import org.omg.CORBA.*;
import org.omg.CosNaming.*;

public class NameClientList
{
   public static void main(String args[])
   {
      try {

        Properties props = new Properties();
        props.put("org.omg.CORBA.ORBInitialPort", "1050");
        ORB orb = ORB.init(args, props);

        NamingContext nc = NamingContextHelper.narrow(orb.resolve_initial_references("NameService"));

 
        BindingListHolder bl = new BindingListHolder();
        BindingIteratorHolder blIt= new BindingIteratorHolder();
        nc.list(1000, bl, blIt);

        Binding bindings[] = bl.value;
        if (bindings.length == 0) return;

        for (int i=0; i < bindings.length; i++) {

            // get the object reference for each binding
            org.omg.CORBA.Object obj = nc.resolve(bindings[i].binding_name);
            String objStr = orb.object_to_string(obj);
            int lastIx = bindings[i].binding_name.length-1;

            // check to see if this is a naming context
            if (bindings[i].binding_type == BindingType.ncontext) {
              System.out.println( "Context: " + bindings[i].binding_name[lastIx].id);
            } else {
                System.out.println("Object: " + bindings[i].binding_name[lastIx].id);
            }
        }

       } catch (Exception e) {
        e.printStackTrace(System.err);
       } 
   }
}