001/*
002 * Licensed to the Apache Software Foundation (ASF) under one
003 * or more contributor license agreements.  See the NOTICE file
004 * distributed with this work for additional information
005 * regarding copyright ownership.  The ASF licenses this file
006 * to you under the Apache License, Version 2.0 (the
007 * "License"); you may not use this file except in compliance
008 * with the License.  You may obtain a copy of the License at
009 *
010 *   http://www.apache.org/licenses/LICENSE-2.0
011 *
012 * Unless required by applicable law or agreed to in writing,
013 * software distributed under the License is distributed on an
014 * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
015 * KIND, either express or implied.  See the License for the
016 * specific language governing permissions and limitations
017 * under the License.
018 */
019package org.eclipse.aether;
020
021import java.util.function.Supplier;
022
023/**
024 * A container for data that is specific to a repository system session. Both components within the repository system
025 * and clients of the system may use this storage to associate arbitrary data with a session.
026 * <p>
027 * Unlike a cache, this session data is not subject to purging. For this same reason, session data should also not be
028 * abused as a cache (i.e. for storing values that can be re-calculated) to avoid memory exhaustion.
029 * <p>
030 * <strong>Note:</strong> Actual implementations must be thread-safe.
031 *
032 * @see RepositorySystemSession#getData()
033 * @noimplement This interface is not intended to be implemented by clients.
034 * @noextend This interface is not intended to be extended by clients.
035 */
036public interface SessionData {
037
038    /**
039     * Associates the specified session data with the given key.
040     *
041     * @param key The key under which to store the session data, must not be {@code null}.
042     * @param value The data to associate with the key, may be {@code null} to remove the mapping.
043     */
044    void set(Object key, Object value);
045
046    /**
047     * Associates the specified session data with the given key if the key is currently mapped to the given value. This
048     * method provides an atomic compare-and-update of some key's value.
049     *
050     * @param key The key under which to store the session data, must not be {@code null}.
051     * @param oldValue The expected data currently associated with the key, may be {@code null}.
052     * @param newValue The data to associate with the key, may be {@code null} to remove the mapping.
053     * @return {@code true} if the key mapping was successfully updated from the old value to the new value,
054     *         {@code false} if the current key mapping didn't match the expected value and was not updated.
055     */
056    boolean set(Object key, Object oldValue, Object newValue);
057
058    /**
059     * Gets the session data associated with the specified key.
060     *
061     * @param key The key for which to retrieve the session data, must not be {@code null}.
062     * @return The session data associated with the key or {@code null} if none.
063     */
064    Object get(Object key);
065
066    /**
067     * Retrieve of compute the data associated with the specified key.
068     *
069     * @param key The key for which to retrieve the session data, must not be {@code null}.
070     * @param supplier The supplier will compute the new value.
071     * @return The session data associated with the key.
072     */
073    Object computeIfAbsent(Object key, Supplier<Object> supplier);
074}