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NamingServiceImpl.java

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/**************************************************************************
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       disclaimer in the documentation and/or other materials provided
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       written permission.

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package org.hebe.mps;

import org.hebe.mps.naming.Binding;
import org.hebe.mps.naming.NamingServiceServer;
import java.util.Hashtable;
import java.util.Enumeration;
import java.net.*;

/**
 * Implementation class for the MPS Server Interface defined in
 * ../namingservice.mps. MPS uses an MPS server to locate its own
 * server names!
 *
 * <p>
 * Note that this class has a <code>main</code> method - it is its
 * own application as well: a standalone MPS name server.
 *
 * @author Tony Garnock-Jones <tonyg@kcbbs.gen.nz>
 */
public class NamingServiceImpl implements org.hebe.mps.naming.NamingService {
    /**
     * Main method for the standalone naming server.
     */
    public static void main(String [] args) {
        if (args.length > 2 || (args.length > 0 && args[0].equals("-h"))) {
            usage();
            return;
        }

        int portNumber = 9091;
        InetAddress hostname = null;

        if (args.length > 0) {
            try {
                portNumber = Integer.parseInt(args[0]);
            } catch (NumberFormatException nfe) {
                System.out.println("Invalid port number.");
                usage();
                return;
            }
        }

        if (args.length > 1) {
            try {
                hostname = InetAddress.getByName(args[1]);
            } catch (UnknownHostException uhe) {
                System.out.println("Unknown host \"" + args[1] + "\"");
                return;
            }
        }

        try {
            NamingServiceImpl impl = new NamingServiceImpl();
            NamingServiceServer svr =
                new NamingServiceServer("NamingService", hostname, portNumber, impl);
            impl.bind("NamingService", svr.getBoundName(), true);
        } catch (Exception e) {
            e.printStackTrace();
        }
    }

    /**
     * Display a friendly application-usage message to stdout.
     */
    public static void usage() {
        System.out.println("Usage: org.hebe.mps.NamingServiceImpl [<portnumber>] [<hostname>]");
        System.out.println("    <portnumber> defaults to 9091");
        System.out.println("    <hostname> defaults to INADDR_ANY");
    }

    ///////////////////////////////////////////////////////////////////////////

    /**
     * This class uses a naive hashtable-lookup to map objectNames
     * onto resolvedNames (aka canonical names).
     */
    private Hashtable names = new Hashtable();

    public NamingServiceImpl() {
    }

    /**
     * Implement the naming-service resolution function.
     *
     * @param name the objectName to look up
     * @return the results of the lookup - an address, or the empty-string
     */
    public String resolve(String name) {
        if (name.startsWith("mps:"))
            return name;

        if (names.containsKey(name)) {
            String result = (String) names.get(name);
            if (result != null)
                return result;
        }

        return "";
    }

    /**
     * Implement the naming-service name binding function.
     *
     * @param name the object name to use
     * @param cname the canonical name to use
     * @param replace whether to replace any potential existing bindings with the same name or not
     * @return true if the bind succeeded; false if an existing binding was not replaced
     */
    public boolean bind(String name, String cname, boolean replace) {
        if (name.startsWith("mps:"))
            return true;

        if (names.containsKey(name) && !replace)
            return false;

        System.out.println("Binding \"" + name + "\" to \"" + cname + "\"");
        names.put(name, cname);
        return true;
    }

    /**
     * Implement the naming-service name unbinding function.
     *
     * @param name the name to remove from this nameserver
     * @return true if the name was removed; false if it was not bound in the first place
     */
    public boolean unbind(String name) {
        if (names.containsKey(name) &&
            names.get(name) != null) {
            names.put(name, null);
            return true;
        }

        return false;
    }

    /**
     * Get a list of all the name-value pairs in the current running
     * database.
     *
     * @return an array of Result structures containing every map in the hashtable
     */
    public Binding[] enumerate() {
        Binding[] results = new Binding[names.size()];
        int i = 0;

        for (Enumeration e = names.keys();
             e.hasMoreElements();
             i++) {
            String name = (String) e.nextElement();
            String cname = (String) names.get(name);
            results[i] = new Binding(name, cname);
        }
        return results;
    }
}

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