src/java/org/apache/nutch/util/NutchConfiguration.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.apache.nutch.util;

import java.util.Map.Entry;
import java.util.Properties;
import java.util.UUID;

import org.apache.hadoop.conf.Configuration;

/**
 * Utility to create Hadoop {@link Configuration}s that include Nutch-specific
 * resources.
 */
public class NutchConfiguration {
  public static final String UUID_KEY = "nutch.conf.uuid";

  private NutchConfiguration() {
  } // singleton

  /*
   * Configuration.hashCode() doesn't return values that correspond to a unique
   * set of parameters. This is a workaround so that we can track instances of
   * Configuration created by Nutch.
   */
  private static void setUUID(Configuration conf) {
    UUID uuid = UUID.randomUUID();
    conf.set(UUID_KEY, uuid.toString());
  }

  /**
   * Retrieve a Nutch UUID of this configuration object, or null if the
   * configuration was created elsewhere.
   * 
   * @param conf
   *          configuration instance
   * @return uuid or null
   */
  public static String getUUID(Configuration conf) {
    return conf.get(UUID_KEY);
  }

  /**
   * Create a {@link Configuration} for Nutch. This will load the standard Nutch
   * resources, <code>nutch-default.xml</code> and <code>nutch-site.xml</code>
   * overrides.
   */
  public static Configuration create() {
    Configuration conf = new Configuration();
    setUUID(conf);
    addNutchResources(conf);
    return conf;
  }

  /**
   * Create a {@link Configuration} from supplied properties.
   * 
   * @param addNutchResources
   *          if true, then first <code>nutch-default.xml</code>, and then
   *          <code>nutch-site.xml</code> will be loaded prior to applying the
   *          properties. Otherwise these resources won't be used.
   * @param nutchProperties
   *          a set of properties to define (or override)
   */
  public static Configuration create(boolean addNutchResources,
      Properties nutchProperties) {
    Configuration conf = new Configuration();
    setUUID(conf);
    if (addNutchResources) {
      addNutchResources(conf);
    }
    for (Entry<Object, Object> e : nutchProperties.entrySet()) {
      conf.set(e.getKey().toString(), e.getValue().toString());
    }
    return conf;
  }

  /**
   * Add the standard Nutch resources to {@link Configuration}.
   * 
   * @param conf
   *          Configuration object to which configuration is to be added.
   */
  private static Configuration addNutchResources(Configuration conf) {
    conf.addResource("nutch-default.xml");
    conf.addResource("nutch-site.xml");
    return conf;
  }
}