core/src/main/java/org/jclouds/config/ValueOfConfigurationKeyOrNull.java

/*
 * 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.config;

import static com.google.common.base.Preconditions.checkNotNull;
import static com.google.inject.name.Names.named;

import javax.inject.Inject;

import com.google.common.base.Function;
import com.google.inject.ConfigurationException;
import com.google.inject.Injector;
import com.google.inject.Key;

public class ValueOfConfigurationKeyOrNull implements Function<String, String> {
   private final Injector injector;

   @Inject
   private ValueOfConfigurationKeyOrNull(Injector injector) {
      this.injector = checkNotNull(injector, "injector");
   }

   @Override
   public String apply(String configurationKey) {
      checkNotNull(configurationKey, "configurationKey");
      try {
         return injector.getInstance(Key.get(String.class, named(configurationKey)));
      } catch (ConfigurationException e) {
         return null;
      }
   }
}