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A JSR330 style dependency injection solution
There is a newer version: 1.13.2
package org.osgl.inject;

/*-
 * #%L
 * OSGL Genie
 * %%
 * Copyright (C) 2017 OSGL (Open Source General Library)
 * %%
 * Licensed 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.
 * #L%
 */

import org.osgl.$;

import javax.inject.Named;

/**
 * A `KeyExtractor` can be used to extract or derive "key" from
 * a value data. The result "key" can be used to index the value
 * in a {@link java.util.Map} data structure.
 *
 * A general contract implementation must obey is
 * different value must generate different key
 *
 * @param  generic type of the key
 * @param  generic type of the value
 */
public interface KeyExtractor {
    /**
     * Get the key of data.
     *
     * @param hint
     *      optional, a string value provides hint to extract key
     * @param data
     *      the value data
     * @return
     *      the key of the data
     */
    K keyOf(String hint, V data);

    /**
     * An implementation of {@link KeyExtractor} that extract
     * property (specified through `hint` parameter) from a
     * java bean (data).
     */
    class PropertyExtractor implements KeyExtractor {
        @Override
        public Object keyOf(String hint, Object data) {
            return $.getProperty(data, hint);
        }
    }

    /**
     * An implementation of {@link KeyExtractor} that extract the
     * value specified in {@link Named} annotation marked on the class
     * of a java bean (data)
     */
    class NamedClassNameExtractor implements KeyExtractor {

        private Class mapKeyType;

        public NamedClassNameExtractor(Class mapKeyType) {
            this.mapKeyType = null == mapKeyType ? String.class : mapKeyType;
        }

        @Override
        public Object keyOf(String hint, Object data) {
            if (null == data) {
                return null;
            }
            Class type;
            if (data instanceof Class) {
                type = (Class) data;
            } else {
                type = data.getClass();
            }
            Named named = type.getAnnotation(Named.class);
            return null == named ? type.getSimpleName() : $.convert(named.value()).to(mapKeyType);
        }
    }

}