org.apache.hadoop.hbase.CompatibilityFactory.java Source code

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Here is the source code for org.apache.hadoop.hbase.CompatibilityFactory.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.hbase;

import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;

import java.util.Iterator;
import java.util.ServiceLoader;

/**
 * Class that will create many instances of classes provided by the hbase-hadoop{1|2}-compat jars.
 */
public class CompatibilityFactory {

    private static final Log LOG = LogFactory.getLog(CompatibilitySingletonFactory.class);
    public static final String EXCEPTION_START = "Could not create  ";
    public static final String EXCEPTION_END = " Is the hadoop compatibility jar on the classpath?";

    /**
     * This is a static only class don't let any instance be created.
     */
    protected CompatibilityFactory() {
    }

    public static synchronized <T> T getInstance(Class<T> klass) {
        T instance = null;
        try {
            ServiceLoader<T> loader = ServiceLoader.load(klass);
            Iterator<T> it = loader.iterator();
            instance = it.next();
            if (it.hasNext()) {
                StringBuilder msg = new StringBuilder();
                msg.append("ServiceLoader provided more than one implementation for class: ").append(klass)
                        .append(", using implementation: ").append(instance.getClass())
                        .append(", other implementations: {");
                while (it.hasNext()) {
                    msg.append(it.next()).append(" ");
                }
                msg.append("}");
                LOG.warn(msg);
            }
        } catch (Exception e) {
            throw new RuntimeException(createExceptionString(klass), e);
        } catch (Error e) {
            throw new RuntimeException(createExceptionString(klass), e);
        }

        // If there was nothing returned and no exception then throw an exception.
        if (instance == null) {
            throw new RuntimeException(createExceptionString(klass));
        }
        return instance;
    }

    protected static String createExceptionString(Class klass) {
        return EXCEPTION_START + klass.toString() + EXCEPTION_END;
    }
}