org.jclouds.suppliers.SupplyKeyMatchingValueOrNull Maven / Gradle / Ivy

Go to download

Show more of this group Show more artifacts with this name
Show all versions of jclouds-core Show documentation

Core components to access jclouds services

There is a newer version: 2.6.0

/*
 * 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. note take care to memoize this using {@link Suppliers#memoize(Supplier)}
 */
public class SupplyKeyMatchingValueOrNull implements Supplier {
   @Resource
   protected Logger logger = Logger.NULL;

   private final Supplier>> supplier;
   private final Supplier valueSupplier;

   public SupplyKeyMatchingValueOrNull(Supplier>> supplier, Supplier 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 map = Maps.transformValues(supplier.get(), Suppliers. supplierFunction());
      K region = ImmutableBiMap.copyOf(map).inverse().get(uri);
      if (region == null && !map.isEmpty()) {
         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;
   }
}