org.apache.hadoop.util.GenericsUtil.java Source code

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Here is the source code for org.apache.hadoop.util.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 org.apache.hadoop.classification.InterfaceAudience;
import org.apache.hadoop.classification.InterfaceStability;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.slf4j.impl.Log4jLoggerAdapter;

/**
 * Contains utility methods for dealing with Java Generics. 
 */
@InterfaceAudience.Private
@InterfaceStability.Unstable
public class GenericsUtil {

    /**
     * Returns the Class object (of type <code>Class&lt;T&gt;</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&lt;T&gt;</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&lt;T&gt;</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
     */
    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&lt;T&gt;</code> to a an array of 
     * <code>T[]</code>. 
     * @param list the list to convert
     * @throws ArrayIndexOutOfBoundsException if the list is empty. 
     * Use {@link #toArray(Class, List)} if the list may be empty.
     */
    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;
        }
        Logger log = LoggerFactory.getLogger(clazz);
        return log instanceof Log4jLoggerAdapter;
    }
}