src/main/java/org/apache/james/postage/classloading/CachedInstanceFactory.java

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 * 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   *
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 * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY       *
 * KIND, either express or implied.  See the License for the    *
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 * under the License.                                           *
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package org.apache.james.postage.classloading;

import java.util.HashMap;
import java.util.Map;

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

/**
 * generic object factory, caching the class object for reuse
 */
public class CachedInstanceFactory {

    private static Log log = LogFactory.getLog(CachedInstanceFactory.class);

    private final static Map<String, Class<?>> classes = new HashMap<String, Class<?>>();

    public static Object createInstance(String classname) {
        Object object = null;

        Class<?> clazz = null;
        // class is configured, but not yet loaded
        if (classname != null && classes.get(classname) == null) {
            try {
                clazz = Class.forName(classname);
            } catch (ClassNotFoundException e) {
                log.error("failed to load class " + classname, e);
            }
        }

        // create instance, if custom class is given
        if (clazz != null) {
            try {
                object = clazz.newInstance();
            } catch (Exception e) {
                log.error("failed to create instance of class " + classname, e);
            }
        }

        return object;
    }

}