/
GenericsUtil.java
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/
GenericsUtil.java
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/**
* 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.util;
import java.lang.reflect.Array;
import java.util.List;
import java.util.concurrent.atomic.AtomicBoolean;
import org.apache.hadoop.classification.InterfaceAudience;
import org.apache.hadoop.classification.InterfaceStability;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
/**
* Contains utility methods for dealing with Java Generics.
*/
@InterfaceAudience.Private
@InterfaceStability.Unstable
public class GenericsUtil {
private static final String SLF4J_LOG4J_ADAPTER_CLASS = "org.slf4j.impl.Reload4jLoggerAdapter";
/**
* Set to false only if log4j adapter class is not found in the classpath. Once set to false,
* the utility method should not bother re-loading class again.
*/
private static final AtomicBoolean IS_LOG4J_LOGGER = new AtomicBoolean(true);
/**
* Returns the Class object (of type <code>Class<T></code>) of the
* argument of type <code>T</code>.
* @param <T> The type of the argument
* @param t the object to get it class
* @return <code>Class<T></code>
*/
public static <T> Class<T> getClass(T t) {
@SuppressWarnings("unchecked")
Class<T> clazz = (Class<T>)t.getClass();
return clazz;
}
/**
* Converts the given <code>List<T></code> to a an array of
* <code>T[]</code>.
* @param c the Class object of the items in the list
* @param list the list to convert
* @param <T> Generics Type T.
* @return T Array.
*/
public static <T> T[] toArray(Class<T> c, List<T> list)
{
@SuppressWarnings("unchecked")
T[] ta= (T[])Array.newInstance(c, list.size());
for (int i= 0; i<list.size(); i++)
ta[i]= list.get(i);
return ta;
}
/**
* Converts the given <code>List<T></code> to a an array of
* <code>T[]</code>.
* @param list the list to convert
* @param <T> Generics Type T.
* @throws ArrayIndexOutOfBoundsException if the list is empty.
* Use {@link #toArray(Class, List)} if the list may be empty.
* @return T Array.
*/
public static <T> T[] toArray(List<T> list) {
return toArray(getClass(list.get(0)), list);
}
/**
* Determine whether the log of <code>clazz</code> is Log4j implementation.
* @param clazz a class to be determined
* @return true if the log of <code>clazz</code> is Log4j implementation.
*/
public static boolean isLog4jLogger(Class<?> clazz) {
if (clazz == null) {
return false;
}
return isLog4jLogger(clazz.getName());
}
/**
* Determine whether the log of the given logger is of Log4J implementation.
*
* @param logger the logger name, usually class name as string.
* @return true if the logger uses Log4J implementation.
*/
public static boolean isLog4jLogger(String logger) {
if (logger == null || !IS_LOG4J_LOGGER.get()) {
return false;
}
Logger log = LoggerFactory.getLogger(logger);
try {
Class<?> log4jClass = Class.forName(SLF4J_LOG4J_ADAPTER_CLASS);
return log4jClass.isInstance(log);
} catch (ClassNotFoundException e) {
IS_LOG4J_LOGGER.set(false);
return false;
}
}
}