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The Apache Log4j API
There is a newer version: 3.0.0-beta2
/*
 * 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.logging.log4j;

import java.util.HashMap;
import java.util.Iterator;
import java.util.Map;

/**
 * Adds entries to the {@link ThreadContext stack or map} and them removes them when the object is closed, e.g. as part
 * of a try-with-resources.
 *
 * @since 2.6
 */
public class CloseableThreadContext {

    private CloseableThreadContext() {
    }

    /**
     * Pushes new diagnostic context information on to the Thread Context Stack. The information will be popped off when
     * the instance is closed.
     *
     * @param message The new diagnostic context information.
     * @return a new instance that will back out the changes when closed.
     */
    public static CloseableThreadContext.Instance push(final String message) {
        return new CloseableThreadContext.Instance().push(message);
    }

    /**
     * Pushes new diagnostic context information on to the Thread Context Stack. The information will be popped off when
     * the instance is closed.
     *
     * @param message The new diagnostic context information.
     * @param args    Parameters for the message.
     * @return a new instance that will back out the changes when closed.
     */
    public static CloseableThreadContext.Instance push(final String message, final Object... args) {
        return new CloseableThreadContext.Instance().push(message, args);
    }

    /**
     * Populates the Thread Context Map with the supplied key/value pairs. Any existing keys in the
     * {@link ThreadContext} will be replaced with the supplied values, and restored back to their original values when
     * the instance is closed.
     *
     * @param key   The  key to be added
     * @param value The value to be added
     * @return a new instance that will back out the changes when closed.
     */
    public static CloseableThreadContext.Instance put(final String key, final String value) {
        return new CloseableThreadContext.Instance().put(key, value);
    }

    public static class Instance implements AutoCloseable {

        private int pushCount = 0;
        private final Map originalValues = new HashMap<>();

        private Instance() {
        }

        /**
         * Pushes new diagnostic context information on to the Thread Context Stack. The information will be popped off when
         * the instance is closed.
         *
         * @param message The new diagnostic context information.
         * @return the instance that will back out the changes when closed.
         */
        public Instance push(final String message) {
            ThreadContext.push(message);
            pushCount++;
            return this;
        }

        /**
         * Pushes new diagnostic context information on to the Thread Context Stack. The information will be popped off when
         * the instance is closed.
         *
         * @param message The new diagnostic context information.
         * @param args    Parameters for the message.
         * @return the instance that will back out the changes when closed.
         */
        public Instance push(final String message, final Object[] args) {
            ThreadContext.push(message, args);
            pushCount++;
            return this;
        }

        /**
         * Populates the Thread Context Map with the supplied key/value pairs. Any existing keys in the
         * {@link ThreadContext} will be replaced with the supplied values, and restored back to their original values when
         * the instance is closed.
         *
         * @param key   The  key to be added
         * @param value The value to be added
         * @return the instance that will back out the changes when closed.
         */
        public Instance put(final String key, final String value) {
            // If there are no existing values, a null will be stored as an old value
            if (!originalValues.containsKey(key)) {
                originalValues.put(key, ThreadContext.get(key));
            }
            ThreadContext.put(key, value);
            return this;
        }

        /**
         * Removes the values from the {@link ThreadContext}.
         * 
         * Values pushed to the {@link ThreadContext} stack will be popped off.
         * 
         * 
         * Values put on the {@link ThreadContext} map will be removed, or restored to their original values it they already existed.
         * 
         */
        @Override
        public void close() {
            closeStack();
            closeMap();
        }

        private void closeMap() {
            for (Iterator> it = originalValues.entrySet().iterator(); it.hasNext(); ) {
                final Map.Entry entry = it.next();
                final String key = entry.getKey();
                final String originalValue = entry.getValue();
                if (null == originalValue) {
                    ThreadContext.remove(key);
                } else {
                    ThreadContext.put(key, originalValue);
                }
                it.remove();
            }
        }

        private void closeStack() {
            for (int i = 0; i < pushCount; i++) {
                ThreadContext.pop();
            }
            pushCount = 0;
        }
    }
}