org.apache.hadoop.fs.shell.CommandFactory 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.fs.shell;
import java.util.Arrays;
import java.util.HashMap;
import java.util.Map;
import org.apache.hadoop.classification.InterfaceAudience;
import org.apache.hadoop.classification.InterfaceStability;
import org.apache.hadoop.conf.Configuration;
import org.apache.hadoop.conf.Configured;
import org.apache.hadoop.util.ReflectionUtils;
import org.apache.hadoop.util.StringUtils;
/** class to search for and register commands */
@InterfaceAudience.Private
@InterfaceStability.Unstable
public class CommandFactory extends Configured {
private Map> classMap =
new HashMap>();
private Map objectMap =
new HashMap();
/** Factory constructor for commands */
public CommandFactory() {
this(null);
}
/**
* Factory constructor for commands
* @param conf the hadoop configuration
*/
public CommandFactory(Configuration conf) {
super(conf);
}
/**
* Invokes "static void registerCommands(CommandFactory)" on the given class.
* This method abstracts the contract between the factory and the command
* class. Do not assume that directly invoking registerCommands on the
* given class will have the same effect.
* @param registrarClass class to allow an opportunity to register
*/
public void registerCommands(Class registrarClass) {
try {
registrarClass.getMethod(
"registerCommands", CommandFactory.class
).invoke(null, this);
} catch (Exception e) {
throw new RuntimeException(StringUtils.stringifyException(e));
}
}
/**
* Register the given class as handling the given list of command
* names.
* @param cmdClass the class implementing the command names
* @param names one or more command names that will invoke this class
*/
public void addClass(Class cmdClass, String ... names) {
for (String name : names) classMap.put(name, cmdClass);
}
/**
* Register the given object as handling the given list of command
* names. Avoid calling this method and use
* {@link #addClass(Class, String...)} whenever possible to avoid
* startup overhead from excessive command object instantiations. This
* method is intended only for handling nested non-static classes that
* are re-usable. Namely -help/-usage.
* @param cmdObject the object implementing the command names
* @param names one or more command names that will invoke this class
*/
public void addObject(Command cmdObject, String ... names) {
for (String name : names) {
objectMap.put(name, cmdObject);
classMap.put(name, null); // just so it shows up in the list of commands
}
}
/**
* Returns an instance of the class implementing the given command. The
* class must have been registered via
* {@link #addClass(Class, String...)}
* @param cmd name of the command
* @return instance of the requested command
*/
public Command getInstance(String cmd) {
return getInstance(cmd, getConf());
}
/**
* Get an instance of the requested command
* @param cmdName name of the command to lookup
* @param conf the hadoop configuration
* @return the {@link Command} or null if the command is unknown
*/
public Command getInstance(String cmdName, Configuration conf) {
if (conf == null) throw new NullPointerException("configuration is null");
Command instance = objectMap.get(cmdName);
if (instance == null) {
Class cmdClass = classMap.get(cmdName);
if (cmdClass != null) {
instance = ReflectionUtils.newInstance(cmdClass, conf);
instance.setName(cmdName);
instance.setCommandFactory(this);
}
}
return instance;
}
/**
* Gets all of the registered commands
* @return a sorted list of command names
*/
public String[] getNames() {
String[] names = classMap.keySet().toArray(new String[0]);
Arrays.sort(names);
return names;
}
}