// This example is from _Java Examples in a Nutshell_. (http://www.oreilly.com)
// Copyright (c) 1997 by David Flanagan
// This example is provided WITHOUT ANY WARRANTY either expressed or implied.
// You may study, use, modify, and distribute it for non-commercial purposes.
// For any commercial use, see http://www.davidflanagan.com/javaexamples
import java.rmi.*;
import java.rmi.server.*;
import java.rmi.registry.*;
import java.io.*;
import java.util.*;
import Mud.*;
/**
* This class implements the RemoteMudPlace interface and exports a
* bunch of remote methods that are at the heart of the MUD. The
* MudClient interacts primarily with these methods. See the comment
* for RemoteMudPlace for an overview.
* The MudPlace class is Serializable so that places can be saved to disk
* along with the MudServer that contains them. Note, however that the
* names and people fields are marked transient, so they are not serialized
* along with the place (because it wouldn't make sense to try to save
* RemoteMudPerson objects, even if they could be serialized).
**/
public class MudPlace extends UnicastRemoteObject
implements RemoteMudPlace, Serializable {
String placename, description; // information about the place itself
Vector exits = new Vector(); // names of exits from this place
Vector destinations = new Vector(); // where the exits go to
Vector things = new Vector(); // names of things in this place
Vector descriptions = new Vector(); // descriptions of those things
transient Vector names = new Vector(); // names of people in this place
transient Vector people = new Vector(); // the RemoteMudPerson objects
MudServer server; // the server for this place
/** A no-arg constructor for de-serialization only. Do not call it */
public MudPlace() throws RemoteException { super(); }
/**
* This constructor creates a place, and calls a server method
* to register the object so that it will be accessible by name
**/
public MudPlace(MudServer server, String placename, String description)
throws RemoteException, PlaceAlreadyExists {
this.server = server;
this.placename = placename;
this.description = description;
server.setPlaceName(this, placename); // Register the place
}
/** This remote method returns the name of this place */
public String getPlaceName() throws RemoteException { return placename; }
/** This remote method returns the description of this place */
public String getDescription() throws RemoteException { return description; }
/** This remote method returns a Vector of names of people in this place */
public Vector getNames() throws RemoteException { return names; }
/** This remote method returns a Vector of names of things in this place */
public Vector getThings() throws RemoteException { return things; }
/** This remote method returns a Vector of names of exits from this place */
public Vector getExits() throws RemoteException { return exits; }
/**
* This remote method returns a RemoteMudPerson object corresponding to
* the specified name, or throws an exception if no such person is here
**/
public RemoteMudPerson getPerson(String name)
throws RemoteException, NoSuchPerson {
synchronized(names) {
// What about when there are 2 of the same name?
int i = names.indexOf(name);
if (i == -1) throw new NoSuchPerson();
return (RemoteMudPerson) people.elementAt(i);
}
}
/**
* This remote method returns a description of the named thing, or
* throws an exception if no such thing is in this place.
**/
public String examineThing(String name) throws RemoteException, NoSuchThing {
synchronized(things) {
int i = things.indexOf(name);
if (i == -1) throw new NoSuchThing();
return (String) descriptions.elementAt(i);
}
}
/**
* This remote method moves the specified RemoteMudPerson from this place
* in the named direction (i.e. through the named exit) to whatever place
* is there. It throws exceptions if the specified person isn't in this
* place to begin with, or if they are already in the place through the exit
* or if the exit doesn't exist, or if the exit links to another MUD server
* and the server is not functioning.
**/
public RemoteMudPlace go(RemoteMudPerson who, String direction)
throws RemoteException, NotThere, AlreadyThere, NoSuchExit, LinkFailed {
// Make sure the direction is valid, and get destination if it is
Object destination;
synchronized(exits) {
int i = exits.indexOf(direction);
if (i == -1) throw new NoSuchExit();
destination = destinations.elementAt(i);
}
// If destination is a string, it is a place on another server, so connect
// to that server. Otherwise, it is a place already on this server.
// Throw an exception if we can't connect to the server.
RemoteMudPlace newplace;
if (destination instanceof String) {
try {
String t = (String) destination;
int pos = t.indexOf('@');
String url = t.substring(0, pos);
String placename = t.substring(pos+1);
RemoteMudServer s = (RemoteMudServer) Naming.lookup(url);
newplace = s.getNamedPlace(placename);
}
catch (Exception e) { throw new LinkFailed(); }
}
// If the destination is not a string, then it is a Place
else newplace = (RemoteMudPlace) destination;
// Make sure the person is here and get their name.
// Throw an exception if they are not here
String name = verifyPresence(who);
// Move the person out of here, and tell everyone who remains about it.
this.exit(who, name + " has gone " + direction);
// Put the person into the new place.
// Send a message to everyone already in that new place
String fromwhere;
if (newplace instanceof MudPlace) // going to a local place
fromwhere = placename;
else
fromwhere = server.getMudName() + "." + placename;
newplace.enter(who, name, name + " has arrived from: " + fromwhere);
// Return the new RemoteMudPlace object to the client so they
// know where they are now at.
return newplace;
}
/**
* This remote method sends a message to everyone in the room. Used to
* say things to everyone. Requires that the speaker be in this place.
**/
public void speak(RemoteMudPerson speaker, String msg)
throws RemoteException, NotThere {
String name = verifyPresence(speaker);
tellEveryone(name + ":" + msg);
}
/**
* This remote method sends a message to everyone in the room. Used to
* do things that people can see. Requires that the actor be in this place.
**/
public void act(RemoteMudPerson actor, String msg)
throws RemoteException, NotThere {
String name = verifyPresence(actor);
tellEveryone(name + " " + msg);
}
/**
* This remote method creates a new thing in this room.
* It requires that the creator be in this room.
**/
public void createThing(RemoteMudPerson creator,
String name, String description)
throws RemoteException, NotThere, AlreadyThere {
// Make sure the creator is here
String creatorname = verifyPresence(creator);
synchronized(things) {
// Make sure there isn't already something with this name.
if (things.indexOf(name) != -1) throw new AlreadyThere();
// Add the thing name and descriptions to the appropriate lists
things.addElement(name);
descriptions.addElement(description);
}
// Tell everyone about the new thing and its creator
tellEveryone(creatorname + " has created a " + name);
}
/**
* Remove a thing from this room. Throws exceptions if the person
* who removes it isn't themselves in the room, or if there is no
* such thing here.
**/
public void destroyThing(RemoteMudPerson destroyer, String thing)
throws RemoteException, NotThere, NoSuchThing {
// Verify that the destroyer is here
String name = verifyPresence(destroyer);
synchronized(things) {
// Verify that there is a thing by that name in this room
int i = things.indexOf(thing);
if (i == -1) throw new NoSuchThing();
// And remove its name and description from the lists
things.removeElementAt(i);
descriptions.removeElementAt(i);
}
// Let everyone know of the demise of this thing.
tellEveryone(name + " had destroyed the " + thing);
}
/**
* Create a new place in this MUD, with the specified name an description.
* The new place is accessible from this place through
* the specified exit, and this place is accessible from the new place
* through the specified entrance. The creator must be in this place
* in order to create a exit from this place.
**/
public void createPlace(RemoteMudPerson creator,
String exit, String entrance, String name,
String description)
throws RemoteException,NotThere,ExitAlreadyExists,PlaceAlreadyExists {
// Verify that the creator is actually here in this place
String creatorname = verifyPresence(creator);
synchronized(exits) { // Only allow one client to change exits at a time
// Check that the exit doesn't already exist.
if (exits.indexOf(exit) != -1) throw new ExitAlreadyExists();
// Create the new place, registering its name with the server
MudPlace destination = new MudPlace(server, name, description);
// Link from there back to here
destination.exits.addElement(entrance);
destination.destinations.addElement(this);
// And link from here to there
exits.addElement(exit);
destinations.addElement(destination);
}
// Let everyone know about the new exit, and the new place beyond
tellEveryone(creatorname + " has created a new place: " + exit);
}
/**
* Create a new exit from this mud, linked to a named place in a named
* MUD on a named host (this can also be used to link to a named place in
* the current MUD, of course). Because of the possibilities of deadlock,
* this method only links from here to there; it does not create a return
* exit from there to here. That must be done with a separate call.
**/
public void linkTo(RemoteMudPerson linker, String exit,
String hostname, String mudname, String placename)
throws RemoteException, NotThere, ExitAlreadyExists, NoSuchPlace {
// Verify that the linker is actually here
String name = verifyPresence(linker);
// Check that the link target actually exists. Throw NoSuchPlace if not.
// Note that NoSuchPlace may also mean "NoSuchMud" or "MudNotResponding".
String url = "rmi://" + hostname + '/' + Mud.mudPrefix + mudname;
try {
RemoteMudServer s = (RemoteMudServer) Naming.lookup(url);
RemoteMudPlace destination = s.getNamedPlace(placename);
}
catch (Exception e) { throw new NoSuchPlace(); }
synchronized(exits) {
// Check that the exit doesn't already exist.
if (exits.indexOf(exit) != -1) throw new ExitAlreadyExists();
// Add the exit, to the list of exit names
exits.addElement(exit);
// And add the destination to the list of destinations. Note that
// the destination is stored as a string rather than as a RemoteMudPlace.
// This is because if the remote server goes down then comes back up
// again, a RemoteMudPlace is not valid, but the string still is.
destinations.addElement(url + '@' + placename);
}
// Let everyone know about the new exit and where it leads
tellEveryone(name + " has linked " + exit + " to " +
"'" + placename + "' in MUD '" + mudname +
"' on host " + hostname);
}
/**
* Close an exit that leads out of this place.
* It does not close the return exit from there back to here.
* Note that this method does not destroy the place that the exit leads to.
* In the current implementation, there is no way to destroy a place.
**/
public void close(RemoteMudPerson who, String exit)
throws RemoteException, NotThere, NoSuchExit {
// check that the person closing the exit is actually here
String name = verifyPresence(who);
synchronized(exits) {
// Check that the exit exists
int i = exits.indexOf(exit);
if (i == -1) throw new NoSuchExit();
// Remove it and its destination from the lists
exits.removeElementAt(i);
destinations.removeElementAt(i);
}
// Let everyone know that the exit doesn't exist anymore
tellEveryone(name + " has closed exit " + exit);
}
/**
* Remove a person from this place. If there is a message, send it to
* everyone who is left in this place. If the specified person is not here,
* this method does nothing and does not throw an exception. This method
* is called by go(), and the client should call it when the user quits.
* The client should not allow the user to invoke it directly, however.
**/
public void exit(RemoteMudPerson who, String message) throws RemoteException{
String name;
synchronized(names) {
int i = people.indexOf(who);
if (i == -1) return;
names.removeElementAt(i);
people.removeElementAt(i);
}
if (message != null) tellEveryone(message);
}
/**
* This method puts a person into this place, assigning them the
* specified name, and displaying a message to anyone else who is in
* that place. This method is called by go(), and the client should
* call it to initially place a person into the MUD. Once the person
* is in the MUD, however, the client should restrict them to using go()
* and should not allow them to call this method directly.
* If there have been networking problems, a client might call this method
* to restore a person to this place, in case they've been bumped out.
* (A person will be bumped out of a place if the server tries to send
* a message to them and gets a RemoteException.)
**/
public void enter(RemoteMudPerson who, String name, String message)
throws RemoteException, AlreadyThere {
// Send the message to everyone who is already here.
if (message != null) tellEveryone(message);
// Add the person to this place.
synchronized (names) {
if (people.indexOf(who) != -1) throw new AlreadyThere();
names.addElement(name);
people.addElement(who);
}
}
/**
* This final remote method returns the server object for the MUD in which
* this place exists. The client should not allow the user to invoke this
* method.
**/
public RemoteMudServer getServer() throws RemoteException { return server; }
/**
* Create and start a thread that sends out a message everyone in this place.
* If it gets a RemoteException talking to a person, it silently removes
* that person from this place. This is not a remote method, but is used
* internally by a number of remote methods.
**/
protected void tellEveryone(final String message) {
// If there is no-one here, don't bother sending the message!
if (people.size() == 0) return;
// Make a copy of the people here now. The message is sent asynchronously
// and the list of people in the room may change before the message is
// sent to everyone.
final Vector recipients = (Vector) people.clone();
// Create and start a thread to send the message, using an anonymous
// class. We do this because sending the message to everyone in this
// place might take some time, (particularly on a slow or flaky network)
// and we don't want to wait.
new Thread() {
public void run() {
// Loop through the recipients
for(int i = 0; i < recipients.size(); i++) {
RemoteMudPerson person = (RemoteMudPerson)recipients.elementAt(i);
// Try to send the message to each one.
try { person.tell(message); }
// If it fails, assume that that person's client or network has
// failed, and silently remove them from this place.
catch (RemoteException e) {
try { MudPlace.this.exit(person, null); }
catch (Exception ex) {}
}
}
}
}.start();
}
/**
* This convenience method checks whether the specified person is here.
* If so, it returns their name. If not it throws a NotThere exception
**/
protected String verifyPresence(RemoteMudPerson who) throws NotThere {
int i = people.indexOf(who);
if (i == -1) throw new NotThere();
else return (String) names.elementAt(i);
}
/**
* This method is used for custom de-serialization. Since the vectors of
* people and of their names are transient, they are not serialized with
* the rest of this place. Therefore, when the place is de-serialized, those
* vectors have to be recreated (empty).
**/
private void readObject(ObjectInputStream in)
throws IOException, ClassNotFoundException {
in.defaultReadObject(); // Read most of the object as normal
names = new Vector(); // Then recreate the names vector
people = new Vector(); // and recreate the people vector
}
/** This constant is a version number for serialization */
static final long serialVersionUID = 5090967989223703026L;
}
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