LinkedHashMultimap.java

package tc.oc.commons.core.util;

import java.util.Collection;
import java.util.HashMap;
import java.util.LinkedHashSet;
import java.util.Set;

import com.google.common.base.Supplier;
import com.google.common.collect.ForwardingSetMultimap;
import com.google.common.collect.Multimaps;
import com.google.common.collect.SetMultimap;

/**
 * {@link SetMultimap} that preserves the insertion order of values
 */
public class LinkedHashMultimap<K, V> extends ForwardingSetMultimap<K, V> {

    private final SetMultimap<K, V> delegate = Multimaps.newSetMultimap(
        new HashMap<K, Collection<V>>(),
        new Supplier<Set<V>>() {
            @Override
            public Set<V> get() {
                return new LinkedHashSet<V>();
            }
        }
    );

    @Override
    protected SetMultimap<K, V> delegate() {
        return delegate;
    }

    /**
     * Add the given key-value pair to the map, forcing the value to the end
     * of the key's list if it is already present.
     */
    public boolean force(K key, V value) {
        boolean added = !remove(key, value);
        put(key, value);
        return added;
    }
}