一个允许按值快速查找键的Java multimap

Question

我有一个multimap(类似于Guava提供的):

Multimap<K, V>

，逻辑上可以理解为:

Map<K, Set<V>>

在我的multimap中的数据，有唯一的键和唯一的值。也就是说，不能将相同的值赋给多个键。

除了维护两个Map结构外，有没有人知道一个现有的类/api可以通过键或值给我快速查找。

。

Collection<V> get(K)
...and...
K getKeyByValue(V)

顺便说一句，Map必须是可变的，也就是说，我的数据一直在变化。(对于不可变的Map, Guava提供了一个ImmutableMultimap.inverse()，如果我的Map可以不可变的话，它可以解决这个问题。)

Answer 1

试试这个

import java.util.Collection;
import java.util.Map;
import java.util.Set;
import java.util.Map.Entry;
import com.google.common.collect.ArrayListMultimap;
import com.google.common.collect.Maps;
import com.google.common.collect.Multimap;
import com.google.common.collect.Multiset;
public class MyMap<K, V> implements Multimap<K, V> {
    private Multimap<K, V> key2Value = ArrayListMultimap.create();
    private Map<V, K> value2key = Maps.newHashMap();
    public K getKeyByValue(V value) {
        return value2key.get(value);
    }
    @Override
    public int size() {
        return key2Value.size();
    }
    @Override
    public boolean isEmpty() {
        return key2Value.isEmpty();
    }
    @Override
    public boolean containsKey(Object key) {
        return key2Value.containsKey(key);
    }
    @Override
    public boolean containsValue(Object value) {
        return key2Value.containsValue(value);
    }
    @Override
    public boolean containsEntry(Object key, Object value) {
        return key2Value.containsEntry(key, value);
    }
    @Override
    public boolean put(K key, V value) {
        value2key.put(value, key);
        return key2Value.put(key, value);
    }
    @Override
    public boolean remove(Object key, Object value) {
        value2key.remove(value);
        return key2Value.remove(key, value);
    }
    @Override
    public boolean putAll(K key, Iterable<? extends V> values) {
        for (V value : values) {
            value2key.put(value, key);
        }
        return key2Value.putAll(key, values);
    }
    @Override
    public boolean putAll(Multimap<? extends K, ? extends V> multimap) {
        for (Entry<? extends K, ? extends V> e : multimap.entries()) {
            value2key.put(e.getValue(), e.getKey());
        }
        return key2Value.putAll(multimap);
    }
    @Override
    public Collection<V> replaceValues(K key, Iterable<? extends V> values) {
        Collection<V> replaced = key2Value.replaceValues(key, values);
        for (V value : replaced) {
            value2key.remove(value);
        }
        for (V value : values) {
            value2key.put(value, key);
        }
        return replaced;
    }
    @Override
    public Collection<V> removeAll(Object key) {
        Collection<V> removed = key2Value.removeAll(key);
        for (V value : removed) {
            value2key.remove(value);
        }
        return removed;
    }
    @Override
    public void clear() {
        value2key.clear();
        key2Value.clear();
    }
    @Override
    public Collection<V> get(K key) {
        return key2Value.get(key);
    }
    @Override
    public Set<K> keySet() {
        return key2Value.keySet();
    }
    @Override
    public Multiset<K> keys() {
        return key2Value.keys();
    }
    @Override
    public Collection<V> values() {
        return key2Value.values();
    }
    @Override
    public Collection<Entry<K, V>> entries() {
        return key2Value.entries();
    }
    @Override
    public Map<K, Collection<V>> asMap() {
        return key2Value.asMap();
    }
    public static void main(String[] args) {
        MyMap<String, String> map = new MyMap<>();
        map.put("key1", "value1");
        map.put("key1", "value2");
        map.put("key1", "value3");
        map.put("key1", "value4");
        map.put("key2", "value5");
        System.out.println(map.getKeyByValue("value1"));
        System.out.println(map.getKeyByValue("value5"));
    }
}

:

key1
key2

Answer 2

我想你可能需要这个类:org.apache.commons.collections.map.MultiValueMap

它是ASF commons-collections.jar,document: http://commons.apache.org/proper/commons-collections/javadocs/api-3.2.1/org/apache/commons/collections/map/MultiValueMap.html