| /* |
| * 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.commons.chain2; |
| |
| import java.util.Map; |
| |
| /** |
| * <p>A {@link Context} represents the state information that is |
| * accessed and manipulated by the execution of a {@link Command} or a |
| * {@link Chain}. Specialized implementations of {@link Context} will |
| * typically add JavaBeans properties that contain typesafe accessors |
| * to information that is relevant to a particular use case for this |
| * context, and/or add operations that affect the state information |
| * that is saved in the context.</p> |
| * |
| * <p>Implementations of {@link Context} must also implement all of the |
| * required and optional contracts of the <code>java.util.Map</code> |
| * interface.</p> |
| * |
| * <p>It is strongly recommended, but not required, that JavaBeans |
| * properties added to a particular {@link Context} implementation exhibit |
| * <em>Attribute-Property Transparency</em>. In other words, |
| * a value stored via a call to <code>setFoo(value)</code> should be visible |
| * by calling <code>get("foo")</code>, and a value stored |
| * via a call to <code>put("foo", value)</code> should be |
| * visible by calling <code>getFoo()</code>. If your {@link Context} |
| * implementation class exhibits this featue, it becomes easier to reuse the |
| * implementation in multiple environments, without the need to cast to a |
| * particular implementation class in order to access the property getter |
| * and setter methods.</p> |
| * |
| * <p>To protect applications from evolution of this interface, specialized |
| * implementations of {@link Context} should generally be created by extending |
| * the provided base class ({@link org.apache.commons.chain2.impl.ContextBase}) |
| * rather than directly implementing this interface.</p> |
| * |
| * <p>Applications should <strong>NOT</strong> assume that |
| * {@link Context} implementations, or the values stored in its |
| * attributes, may be accessed from multiple threads |
| * simultaneously unless this is explicitly documented for a particular |
| * implementation.</p> |
| * |
| * @param <K> the type of keys maintained by the context associated with this catalog |
| * @param <V> the type of mapped values |
| * @version $Id$ |
| */ |
| public interface Context<K, V> extends Map<K, V> { |
| |
| /** |
| * That method enhances the {@link #get(Object)} method that helps users |
| * avoid the redundant code of type cast/checking when assignments are already known. |
| * |
| * It throws {@code ClassCastException} if types are not assignable. |
| * |
| * @param <T> the target assignment type |
| * @param key the key whose associated value is to be returned |
| * @return the value to which the specified key is mapped, |
| * or {@code null} if this map contains no mapping for the key |
| * @see #get(Object) |
| * @since 2.0 |
| */ |
| <T extends V> T retrieve(K key); |
| |
| } |