org.apache.hadoop.lib.server.BaseService Maven / Gradle / Ivy
/**
* 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.hadoop.lib.server;
import org.apache.hadoop.classification.InterfaceAudience;
import org.apache.hadoop.conf.Configuration;
import org.apache.hadoop.lib.util.ConfigurationUtils;
import java.util.Map;
/**
* Convenience class implementing the {@link Service} interface.
*/
@InterfaceAudience.Private
public abstract class BaseService implements Service {
private String prefix;
private Server server;
private Configuration serviceConfig;
/**
* Service constructor.
*
* @param prefix service prefix.
*/
public BaseService(String prefix) {
this.prefix = prefix;
}
/**
* Initializes the service.
*
* It collects all service properties (properties having the
* #SERVER#.#SERVICE#. prefix). The property names are then
* trimmed from the #SERVER#.#SERVICE#. prefix.
*
* After collecting the service properties it delegates to the
* {@link #init()} method.
*
* @param server the server initializing the service, give access to the
* server context.
*
* @throws ServiceException thrown if the service could not be initialized.
*/
@Override
public final void init(Server server) throws ServiceException {
this.server = server;
String servicePrefix = getPrefixedName("");
serviceConfig = new Configuration(false);
for (Map.Entry entry : ConfigurationUtils.resolve(server.getConfig())) {
String key = entry.getKey();
if (key.startsWith(servicePrefix)) {
serviceConfig.set(key.substring(servicePrefix.length()), entry.getValue());
}
}
init();
}
/**
* Post initializes the service. This method is called by the
* {@link Server} after all services of the server have been initialized.
*
* This method does a NOP.
*
* @throws ServiceException thrown if the service could not be
* post-initialized.
*/
@Override
public void postInit() throws ServiceException {
}
/**
* Destroy the services. This method is called once, when the
* {@link Server} owning the service is being destroyed.
*
* This method does a NOP.
*/
@Override
public void destroy() {
}
/**
* Returns the service dependencies of this service. The service will be
* instantiated only if all the service dependencies are already initialized.
*
* This method returns an empty array (size 0)
*
* @return an empty array (size 0).
*/
@Override
public Class[] getServiceDependencies() {
return new Class[0];
}
/**
* Notification callback when the server changes its status.
*
* This method returns an empty array (size 0)
*
* @param oldStatus old server status.
* @param newStatus new server status.
*
* @throws ServiceException thrown if the service could not process the status change.
*/
@Override
public void serverStatusChange(Server.Status oldStatus, Server.Status newStatus) throws ServiceException {
}
/**
* Returns the service prefix.
*
* @return the service prefix.
*/
protected String getPrefix() {
return prefix;
}
/**
* Returns the server owning the service.
*
* @return the server owning the service.
*/
protected Server getServer() {
return server;
}
/**
* Returns the full prefixed name of a service property.
*
* @param name of the property.
*
* @return prefixed name of the property.
*/
protected String getPrefixedName(String name) {
return server.getPrefixedName(prefix + "." + name);
}
/**
* Returns the service configuration properties. Property
* names are trimmed off from its prefix.
*
* The sevice configuration properties are all properties
* with names starting with #SERVER#.#SERVICE#.
* in the server configuration.
*
* @return the service configuration properties with names
* trimmed off from their #SERVER#.#SERVICE#.
* prefix.
*/
protected Configuration getServiceConfig() {
return serviceConfig;
}
/**
* Initializes the server.
*
* This method is called by {@link #init(Server)} after all service properties
* (properties prefixed with
*
* @throws ServiceException thrown if the service could not be initialized.
*/
protected abstract void init() throws ServiceException;
}