Key.java

/**
 * 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.s4.base;

import java.util.List;

import org.apache.commons.lang.StringUtils;

/**
 * The Key class is used to get the value of the key on a specific type of event. This is done to abstract all the
 * complexity required to get the value. The method for getting the value is implemented in a method of an object of
 * type KeyFinder<T>.
 * <p>
 * The application programmer provides the events and the corresponding finders. The framework will use it to key on
 * events.
 */
public class Key<T extends Event> {

    final private KeyFinder<T> finder;
    final private String separator;

    public Key(KeyFinder<T> finder, String separator) {
        this.finder = finder;
        this.separator = separator;
    }

    public List<String> getList(T event) {
        return finder.get(event);
    }

    public String get(T event) {
        List<String> keys = getList(event);

        return StringUtils.join(keys, separator);
    }
}