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.util;
018
019import java.io.Serializable;
020import java.util.ArrayList;
021import java.util.List;
022import java.util.Map;
023import java.util.Objects;
024import java.util.concurrent.ConcurrentHashMap;
025import java.util.regex.Matcher;
026import java.util.regex.Pattern;
027
028/**
029 * A source for global configuration properties.
030 *
031 * @since 2.10.0
032 */
033public interface PropertySource {
034
035    /**
036     * Returns the order in which this PropertySource has priority. A higher value means that the source will be
037     * applied later so as to take precedence over other property sources.
038     *
039     * @return priority value
040     */
041    int getPriority();
042
043    /**
044     * Iterates over all properties and performs an action for each key/value pair.
045     *
046     * @param action action to perform on each key/value pair
047     */
048    void forEach(BiConsumer<String, String> action);
049
050    /**
051     * Converts a list of property name tokens into a normal form. For example, a list of tokens such as
052     * "foo", "bar", "baz", might be normalized into the property name "log4j2.fooBarBaz".
053     *
054     * @param tokens list of property name tokens
055     * @return a normalized property name using the given tokens
056     */
057    CharSequence getNormalForm(Iterable<? extends CharSequence> tokens);
058
059    /**
060     * Comparator for ordering PropertySource instances by priority.
061     *
062     * @since 2.10.0
063     */
064    class Comparator implements java.util.Comparator<PropertySource>, Serializable {
065        private static final long serialVersionUID = 1L;
066
067        @Override
068        public int compare(final PropertySource o1, final PropertySource o2) {
069            return Integer.compare(Objects.requireNonNull(o1).getPriority(), Objects.requireNonNull(o2).getPriority());
070        }
071    }
072
073    /**
074     * Utility methods useful for PropertySource implementations.
075     *
076     * @since 2.10.0
077     */
078    final class Util {
079        private static final String PREFIXES = "(?i:^log4j2?[-._/]?|^org\\.apache\\.logging\\.log4j\\.)?";
080        private static final Pattern PROPERTY_TOKENIZER = Pattern.compile(PREFIXES + "([A-Z]*[a-z0-9]+|[A-Z0-9]+)[-._/]?");
081        private static final Map<CharSequence, List<CharSequence>> CACHE = new ConcurrentHashMap<>();
082
083        /**
084         * Converts a property name string into a list of tokens. This will strip a prefix of {@code log4j},
085         * {@code log4j2}, {@code Log4j}, or {@code org.apache.logging.log4j}, along with separators of
086         * dash {@code -}, dot {@code .}, underscore {@code _}, and slash {@code /}. Tokens can also be separated
087         * by camel case conventions without needing a separator character in between.
088         *
089         * @param value property name
090         * @return the property broken into lower case tokens
091         */
092        public static List<CharSequence> tokenize(final CharSequence value) {
093            if (CACHE.containsKey(value)) {
094                return CACHE.get(value);
095            }
096            List<CharSequence> tokens = new ArrayList<>();
097            final Matcher matcher = PROPERTY_TOKENIZER.matcher(value);
098            while (matcher.find()) {
099                tokens.add(matcher.group(1).toLowerCase());
100            }
101            CACHE.put(value, tokens);
102            return tokens;
103        }
104
105        /**
106         * Joins a list of strings using camelCaseConventions.
107         *
108         * @param tokens tokens to convert
109         * @return tokensAsCamelCase
110         */
111        public static CharSequence joinAsCamelCase(final Iterable<? extends CharSequence> tokens) {
112            final StringBuilder sb = new StringBuilder();
113            boolean first = true;
114            for (final CharSequence token : tokens) {
115                if (first) {
116                    sb.append(token);
117                } else {
118                    sb.append(Character.toUpperCase(token.charAt(0)));
119                    if (token.length() > 1) {
120                        sb.append(token.subSequence(1, token.length()));
121                    }
122                }
123                first = false;
124            }
125            return sb.toString();
126        }
127
128        private Util() {
129        }
130    }
131}