org.jclouds.suppliers.SupplyKeyMatchingValueOrNull.java Source code

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Here is the source code for org.jclouds.suppliers.SupplyKeyMatchingValueOrNull.java

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/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package org.jclouds.suppliers;

import java.util.Map;

import javax.annotation.Resource;

import org.jclouds.logging.Logger;

import com.google.common.base.Supplier;
import com.google.common.base.Suppliers;
import com.google.common.collect.ImmutableBiMap;
import com.google.common.collect.Iterables;
import com.google.common.collect.Maps;

/**
 * Allows you to lazy discover a key by value. This is useful for example in service discovery,
 * where you need to see what the "current" service name is based on a map of service names to
 * endpoints. <h3>note</h3> take care to memoize this using {@link Suppliers#memoize(Supplier)}
 * 
 * @author Adrian Cole
 */
public class SupplyKeyMatchingValueOrNull<K, V> implements Supplier<K> {
    @Resource
    protected Logger logger = Logger.NULL;

    private final Supplier<Map<K, Supplier<V>>> supplier;
    private final Supplier<V> valueSupplier;

    public SupplyKeyMatchingValueOrNull(Supplier<Map<K, Supplier<V>>> supplier, Supplier<V> valueSupplier) {
        this.valueSupplier = valueSupplier;
        this.supplier = supplier;
    }

    @Override
    public K get() {
        V uri = valueSupplier.get();
        // eagerly get all the values, so we can see which is default
        Map<K, V> map = Maps.transformValues(supplier.get(), Suppliers.<V>supplierFunction());
        K region = ImmutableBiMap.copyOf(map).inverse().get(uri);
        if (region == null && map.size() > 0) {
            region = Iterables.get(map.keySet(), 0);
            logger.warn("failed to find key for value %s in %s; choosing first: %s", uri, map, region);
        }
        return region;
    }
}