destinationset.java

发布/订阅系统路由重配算法,可应用于ad hoc环境

package broker;

import java.util.*;

import com.Message;
import com.Unsubscription;

import util.*;

public class DestinationSet {
	
	/**
	 * An entry maps a message (or filter) to a destination.
	 * @author parzy
	 *
	 */
	public static class Entry{

		/**
		 * The entry's destination.
		 */
		public final Destination destination;
		
		/**
		 * The entry's message.
		 */
		public final Message message;
		
		/**
		 * The entry's filter.
		 */
		protected final Filter filter;
		
		/**
		 * Creates an entry mapping a message or filter to a destination.
		 * @param entry the original entry from the hashtable.
		 */
		protected Entry(Map.Entry entry){
			Object value;
			this.destination = (Destination)entry.getKey();
			// either a message or a filter is mapped
			value = entry.getValue();
			if(value instanceof Message){
				this.message = (Message)value;
				this.filter = null;
			}else{
				this.message = null;
				this.filter = (Filter)entry.getValue();
			}
		}
		
		/**
		 * Returns the entry's destination.
		 * @return the entry's destination.
		 */
		public Destination getDestintion(){
			return destination;
		}
		
		/**
		 * Returns the entry's message.
		 * @return the entry's message.
		 */
		public Message getMessage(){
			return message;
		}
		
		/**
		 * Returns the entry's filter.
		 * @return the entry's filter.
		 */
		protected Filter getFilter(){
			return filter; 
		}
	}
	
	/**
	 * Provides an iterator of the destination set.
	 * @author parzy
	 */
	protected class SetIterator implements Iterator{
		/**
		 * The iterator provided by the hashtable class.
		 */
		Iterator iterator;
		
		/**
		 * Creates a new set iterator.
		 */
		protected SetIterator(){
			iterator = DestinationSet.this.destinations.entryIterator;
			//entrySet().iterator();
		}
		
		/**
		 * Returns true if the iteration has more elements.
		 * @return true if the iteration has more elements.
		 */
		public boolean hasNext(){
			return iterator.hasNext();
		}
		
		/**
		 * Returns the next element in the iteration.
		 * @return the next element in the iteration.
		 */
		public Object next(){
			return new DestinationSet.Entry((Map.Entry)iterator.next());
		}
		
		/**
		 * Removes from the underlying collection the last element 
		 * returned by the iterator.
		 */
		public void remove(){
			throw new UnsupportedOperationException();
			//iterator.remove();
		}
	}
	
	/**
	 * The underlying hashtable the destination set is based on.
	 */
	protected SimpleHashtable destinations = new SimpleHashtable();
	
	/**
	 * The message or filter to be mapped to added destinations.
	 */
	protected Message message = null;
	
	protected Filter filter = null;
	
	/**
	 * Flag, if adding destinations is allowed.
	 */
	protected boolean restricted = false;

	/**
	 * Creates an empty destination set.
	 */
	public DestinationSet(){}
	
	/**
	 * Creates an empty destination set.
	 * @param message message to be mapped to added destinations.
	 */
	public DestinationSet(Message message){
		this.message = message;
	}
	
	/**
	 * Creates an empty destination set.
	 * @param filter filter to be mapped to added destinations.
	 */
	public DestinationSet(Filter filter){
		this.filter = filter;
	}
	
	/**
	 * Sets the message, which is mapped to all added destinations.
	 * Overrides a filter previously set.
	 * @param message messge which is mapped to all added destinations.
	 */
	public void setMessage(Message message){
		this.message = message;
		this.filter = null;
	}
	
	/**
	 * Returns the last message, which was set.
	 * @return the last message, which was set.
	 */
	public Message getMessage(){
		return message;
	}
	
	/**
	 * Sets the filter, which is mapped to all added destinations.
	 * Overrides a message previously set.
	 * @param filter filter which is mapped to all added destinations.
	 */
	public void setFilter(Filter filter){
		this.filter = filter;
		this.message = null;
	}
	
	/**
	 * Returns the last filter, which was set.
	 * @return the last filter, which was set.
	 */
	public Filter getFilter(){
		return this.filter;
	}

	/**
	 * Returns true, if the destination set maps no destination to a message.
	 * @return true, if the destination set maps no destination to a message,
	 *         otherwise false.
	 */
	public boolean isEmpty(){
		return destinations.isEmpty();
	}
	
	/** 
	 * Clears all destinations.
	 */
	public void clear(){
		destinations.clear();
	}

	/**
	 * Returns a new Iterator to access the elements in the set.
	 * @return a set iterator.
	 */
    public Iterator iterator(){
    	return new SetIterator();
    }
	
	/**
	 * Adds a destination to the set, if it is not restricted.
	 * A previously specified message or filter is mapped to the added
	 * destination.
	 * @param destination the destination to add.
	 */
	public void add(Destination destination){
		if(!restricted){
			if(filter == null){
				destinations.put(destination, message.clone());
			}else{
				destinations.put(destination, filter);
			}
		}
	}
	
	/**
	 * Adds a all destinations to the set, if it is not restricted.
	 * A previously specified message or filter is mapped to the added
	 * destinations.
	 * @param destinations the destinations to add.
	 */
	public void addAll(Collection destinations){
		Destination destination;
		if(!restricted){
			for(Iterator it = destinations.iterator(); it.hasNext(); ) {
				destination = (Destination)it.next();
				this.add(destination);
			}
		}
	}
	
	/**
	 * Removes a destination from the set.
	 * @param destination the destination to remove.
	 */
	public void remove(Destination destination){
		destinations.remove(destination);
	}

	/**
	 * Returns true if the destination set contains the specified destination.
	 * @param destination the destination.
	 * @return true if the destination set contains the specified destination.
	 */
	public boolean contains(Destination destination){
		return destinations.containsKey(destination);
	}
	
	/**
	 * Restricts the set to the specified destination.
	 * If the specified destination is not a member of the set, 
	 * the result is an empty set.
	 * @param destination the specified destination.
	 */
	public void restrictTo(Destination destination){
		Object message;
		message = destinations.get(destination);
		destinations.clear();
		if(message!=null){
			destinations.put(destination, message);
		}
		restricted=true;
	}
	
	/**
	 * Adds all mapped filters to the uncovered subscriptions.
	 * @param uncoveredDestinations a destination set containing the uncovered
	 *        filters with its destinations.
	 */
	public void addFilters(DestinationSet uncoveredDestinations){
		Entry entry;                      // entry of the uncovered destinations
		Unsubscription unsubscription;    // current unsubscription
		
		// for each uncovered filter and destination
		for(Iterator it = uncoveredDestinations.iterator(); it.hasNext(); ){
			entry = (Entry)it.next();
			unsubscription = (Unsubscription)destinations.get(entry.destination);
			unsubscription.getUncoveredFilters().add(entry.filter);
		}
	}
}