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A JavaBean for URLs of the HTTP protocol.
There is a newer version: 0.0.1
package cat.inspiracio.util;

import java.io.Serializable;
import java.util.ArrayList;
import java.util.Collection;
import java.util.Iterator;
import java.util.LinkedHashSet;
import java.util.List;
import java.util.Map;
import java.util.Map.Entry;
import java.util.Set;

/** Like a map, but entries conserve their order and there may be several 
 * entries with the same key. 
 * 
 * A value cannot be null.
 * 
 * Keys and values have to serialisable, because I am interested in serialisable things. */
public class BagMap implements Iterable>, Serializable{
	private static final long serialVersionUID = 2587845281426723243L;

	// state ------------------------------------
	
	private List> entries=new ArrayList>();
	
	// construction ----------------------------
	
	/** Makes a new empty bag map. */
	public BagMap(){}
	
	// business --------------------------------
	
	/** Adds an entry. If the value is null, removes the parameter. 
	 * Returns this, for fluid style. */
	public BagMap add(K key, V value){
		if(value==null){
			remove(key);
			return this;
		}
		Entry entry=new EntryBean(key, value);
		entries.add(entry);
		return this;
	}
	
	/** Gets the value of the first entry with that key, or null if there is none. */
	public V get(K key){
		for(Entry entry : entries){
			if(equals(key, entry.getKey()))
				return entry.getValue();
		}
		return null;
	}
	
	/** Gets all the values for a key, in the order that they were inserted.
	 * Returns a fresh list. */
	public List getValues(K key){
		Listvalues=new ArrayList();
		for(Entry entry : entries){
			K k=entry.getKey();
			if(equals(key, k))
				values.add(entry.getValue());
		}
		return values;
	}

	/** Is there an entry with this key? */
	public boolean containsKey(K key){
        for(Entry entry : entries){
            K k=entry.getKey();
            if(equals(key, k))return true;
        }
        return false;
	}
	
	/** Removes all entries with this key. */
	public void remove(K key){
		Iterator>it=entries.iterator();
		while(it.hasNext()){
			Entry entry=it.next();
			if(equals(key, entry.getKey()))
				it.remove();
		}
	}
	
	/** Sets the first entry with this key to this value and removes all the others. 
	 * If there is no such entry, adds one. 
	 * 
	 * Setting a value to null is removing all. */
	public void set(K key, V value){
		if(value==null){
			remove(key);
			return;
		}
		boolean set=false;
		Iterator>it=entries.iterator();
		while(it.hasNext()){
			Entry entry=it.next();
			if(equals(key, entry.getKey())){
				if(set){
					it.remove();
				}else{
					entry.setValue(value);
					set=true;
				}
			}
		}
		if(!set)
			add(key, value);
	}
	
	public boolean isEmpty(){return entries.isEmpty();}
	public boolean empty(){return isEmpty();}

	/** All the entries in the order they were inserted. */
	@Override public Iterator> iterator(){return entries.iterator();}
	
	/** All the entries in the order they were inserted. */
	public Iterable> iteratable(){return entries;}

    /** All keys that have a value. */
    public Collectionkeys(){
        Setkeys=new LinkedHashSet();
        for(Entry entry : entries){
            K key=entry.getKey();
            keys.add(key);
        }
        return keys;
    }
    
    /** All values. */
    public Collectionvalues(){
        Setvalues=new LinkedHashSet();
        for(Entry entry : entries){
            V v=entry.getValue();
            values.add(v);
        }
        return values;
    }

    /** All entries. */
    public Collection>entries(){return entries;}

	// helpers -----------------------------------------------

    /** Equality without stumbling over null. */
	private boolean equals(K a, K b){
		if(a==null)
			return b==null;
		return a.equals(b);
	}
	
	/** Implementation of interface Entry that is serialisable. */
	private static class EntryBean implements Entry, Serializable{
		private static final long serialVersionUID = -2527497268655890130L;

		private K key;
		private V value;

		EntryBean(K k, V v){key=k; value=v;}
		@Override public K getKey(){return key;}
		@Override public V getValue(){return value;}
		
		@Override public V setValue(V v){
			V old=value;
			value=v;
			return old;
		}
		
		/** Just for debug. */
		@Override public String toString(){
			return key + "->" + value;
		}
	}

}