001/**
002 * Licensed to the Apache Software Foundation (ASF) under one
003 * or more contributor license agreements.  See the NOTICE file
004 * distributed with this work for additional information
005 * regarding copyright ownership.  The ASF licenses this file
006 * to you under the Apache License, Version 2.0 (the
007 * "License"); you may not use this file except in compliance
008 * with the License.  You may obtain a copy of the License at
009 *
010 *     http://www.apache.org/licenses/LICENSE-2.0
011 *
012 * Unless required by applicable law or agreed to in writing, software
013 * distributed under the License is distributed on an "AS IS" BASIS,
014 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
015 * See the License for the specific language governing permissions and
016 * limitations under the License.
017 */
018
019package org.apache.hadoop.lib.server;
020
021import org.apache.hadoop.classification.InterfaceAudience;
022import org.apache.hadoop.conf.Configuration;
023import org.apache.hadoop.lib.util.ConfigurationUtils;
024
025import java.util.Map;
026
027/**
028 * Convenience class implementing the {@link Service} interface.
029 */
030@InterfaceAudience.Private
031public abstract class BaseService implements Service {
032  private String prefix;
033  private Server server;
034  private Configuration serviceConfig;
035
036  /**
037   * Service constructor.
038   *
039   * @param prefix service prefix.
040   */
041  public BaseService(String prefix) {
042    this.prefix = prefix;
043  }
044
045  /**
046   * Initializes the service.
047   * <p/>
048   * It collects all service properties (properties having the
049   * <code>#SERVER#.#SERVICE#.</code> prefix). The property names are then
050   * trimmed from the <code>#SERVER#.#SERVICE#.</code> prefix.
051   * <p/>
052   * After collecting  the service properties it delegates to the
053   * {@link #init()} method.
054   *
055   * @param server the server initializing the service, give access to the
056   * server context.
057   *
058   * @throws ServiceException thrown if the service could not be initialized.
059   */
060  @Override
061  public final void init(Server server) throws ServiceException {
062    this.server = server;
063    String servicePrefix = getPrefixedName("");
064    serviceConfig = new Configuration(false);
065    for (Map.Entry<String, String> entry : ConfigurationUtils.resolve(server.getConfig())) {
066      String key = entry.getKey();
067      if (key.startsWith(servicePrefix)) {
068        serviceConfig.set(key.substring(servicePrefix.length()), entry.getValue());
069      }
070    }
071    init();
072  }
073
074
075  /**
076   * Post initializes the service. This method is called by the
077   * {@link Server} after all services of the server have been initialized.
078   * <p/>
079   * This method does a NOP.
080   *
081   * @throws ServiceException thrown if the service could not be
082   * post-initialized.
083   */
084  @Override
085  public void postInit() throws ServiceException {
086  }
087
088  /**
089   * Destroy the services.  This method is called once, when the
090   * {@link Server} owning the service is being destroyed.
091   * <p/>
092   * This method does a NOP.
093   */
094  @Override
095  public void destroy() {
096  }
097
098  /**
099   * Returns the service dependencies of this service. The service will be
100   * instantiated only if all the service dependencies are already initialized.
101   * <p/>
102   * This method returns an empty array (size 0)
103   *
104   * @return an empty array (size 0).
105   */
106  @Override
107  public Class[] getServiceDependencies() {
108    return new Class[0];
109  }
110
111  /**
112   * Notification callback when the server changes its status.
113   * <p/>
114   * This method returns an empty array (size 0)
115   *
116   * @param oldStatus old server status.
117   * @param newStatus new server status.
118   *
119   * @throws ServiceException thrown if the service could not process the status change.
120   */
121  @Override
122  public void serverStatusChange(Server.Status oldStatus, Server.Status newStatus) throws ServiceException {
123  }
124
125  /**
126   * Returns the service prefix.
127   *
128   * @return the service prefix.
129   */
130  protected String getPrefix() {
131    return prefix;
132  }
133
134  /**
135   * Returns the server owning the service.
136   *
137   * @return the server owning the service.
138   */
139  protected Server getServer() {
140    return server;
141  }
142
143  /**
144   * Returns the full prefixed name of a service property.
145   *
146   * @param name of the property.
147   *
148   * @return prefixed name of the property.
149   */
150  protected String getPrefixedName(String name) {
151    return server.getPrefixedName(prefix + "." + name);
152  }
153
154  /**
155   * Returns the service configuration properties. Property
156   * names are trimmed off from its prefix.
157   * <p/>
158   * The sevice configuration properties are all properties
159   * with names starting with <code>#SERVER#.#SERVICE#.</code>
160   * in the server configuration.
161   *
162   * @return the service configuration properties with names
163   *         trimmed off from their <code>#SERVER#.#SERVICE#.</code>
164   *         prefix.
165   */
166  protected Configuration getServiceConfig() {
167    return serviceConfig;
168  }
169
170  /**
171   * Initializes the server.
172   * <p/>
173   * This method is called by {@link #init(Server)} after all service properties
174   * (properties prefixed with
175   *
176   * @throws ServiceException thrown if the service could not be initialized.
177   */
178  protected abstract void init() throws ServiceException;
179
180}