001/*
002 * Licensed to the Apache Software Foundation (ASF) under one or more
003 * contributor license agreements. See the NOTICE file distributed with
004 * this work for additional information regarding copyright ownership.
005 * The ASF licenses this file to You under the Apache license, Version 2.0
006 * (the "License"); you may not use this file except in compliance with
007 * the License. You may obtain a copy of the License at
008 *
009 *      http://www.apache.org/licenses/LICENSE-2.0
010 *
011 * Unless required by applicable law or agreed to in writing, software
012 * distributed under the License is distributed on an "AS IS" BASIS,
013 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
014 * See the license for the specific language governing permissions and
015 * limitations under the license.
016 */
017package org.apache.logging.log4j.spi;
018
019import java.util.Map;
020
021import org.apache.logging.log4j.ThreadContext;
022import org.apache.logging.log4j.util.StringMap;
023
024/**
025 * Read-only view of the data structure that implements MDC behavior for {@link org.apache.logging.log4j.ThreadContext}.
026 * <p>
027 * {@code ThreadContextMap} implementations that also implement this interface can be accessed
028 * by applications via the {@link ThreadContext#getThreadContextMap()} method.
029 * </p>
030 *
031 * @see ThreadContext#getThreadContextMap()
032 * @since 2.8
033 */
034public interface ReadOnlyThreadContextMap {
035
036    /**
037     * Clears the context.
038     */
039    void clear();
040
041    /**
042     * Determines if the key is in the context.
043     * @param key The key to locate.
044     * @return True if the key is in the context, false otherwise.
045     */
046    boolean containsKey(final String key);
047
048    /**
049     * Gets the context identified by the <code>key</code> parameter.
050     *
051     * <p>This method has no side effects.</p>
052     * @param key The key to locate.
053     * @return The value associated with the key or null.
054     */
055    String get(final String key);
056
057    /**
058     * Gets a non-{@code null} mutable copy of current thread's context Map.
059     * @return a mutable copy of the context.
060     */
061    Map<String, String> getCopy();
062
063    /**
064     * Returns an immutable view on the context Map or {@code null} if the context map is empty.
065     * @return an immutable context Map or {@code null}.
066     */
067    Map<String, String> getImmutableMapOrNull();
068
069    /**
070     * Returns the context data for reading. Note that regardless of whether the returned context data has been
071     * {@linkplain StringMap#freeze() frozen} (made read-only) or not, callers should not attempt to modify
072     * the returned data structure.
073     * <p>
074     * <b>Thread safety note:</b>
075     * </p>
076     * <p>
077     * If this {@code ReadOnlyThreadContextMap} implements {@link CopyOnWrite}, then the returned {@code StringMap} can
078     * safely be passed to another thread: future changes in the underlying context data will not be reflected in the
079     * returned {@code StringMap}.
080     * </p><p>
081     * Otherwise, if this {@code ReadOnlyThreadContextMap} does <em>not</em> implement {@link CopyOnWrite}, then it is
082     * not safe to pass the returned {@code StringMap} to another thread because changes in the underlying context may
083     * be reflected in the returned object. It is the responsibility of the caller to make a copy to pass to another
084     * thread.
085     * </p>
086     *
087     * @return a {@code StringMap} containing context data key-value pairs
088     */
089    StringMap getReadOnlyContextData();
090
091    /**
092     * Returns true if the Map is empty.
093     * @return true if the Map is empty, false otherwise.
094     */
095    boolean isEmpty();
096}