rgoers/log4j2-core/src/main/java/org/apache/logging/log4j/core/pattern/NameAbbreviator.java

/*
 * 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.core.pattern;

import java.util.ArrayList;
import java.util.List;


/**
 * NameAbbreviator generates abbreviated logger and class names.
 */
public abstract class NameAbbreviator {
    /**
     * Default (no abbreviation) abbreviator.
     */
    private static final NameAbbreviator DEFAULT = new NOPAbbreviator();

    /**
     * Gets an abbreviator.
     * <p/>
     * For example, "%logger{2}" will output only 2 elements of the logger name,
     * "%logger{1.}" will output only the first character of the non-final elements in the name,
     * "%logger(1~.2~} will output the first character of the first element, two characters of
     * the second and subsequent elements and will use a tilde to indicate abbreviated characters.
     *
     * @param pattern abbreviation pattern.
     * @return abbreviator, will not be null.
     */
    public static NameAbbreviator getAbbreviator(final String pattern) {
        if (pattern.length() > 0) {
            //  if pattern is just spaces and numbers then
            //     use MaxElementAbbreviator
            String trimmed = pattern.trim();

            if (trimmed.length() == 0) {
                return DEFAULT;
            }

            int i = 0;

            while ((i < trimmed.length()) && (trimmed.charAt(i) >= '0')
                    && (trimmed.charAt(i) <= '9')) {
                i++;
            }

            //
            //  if all blanks and digits
            //
            if (i == trimmed.length()) {
                return new MaxElementAbbreviator(Integer.parseInt(trimmed));
            }

            ArrayList<PatternAbbreviatorFragment> fragments = new ArrayList<PatternAbbreviatorFragment>(5);
            char ellipsis;
            int charCount;
            int pos = 0;

            while ((pos < trimmed.length()) && (pos >= 0)) {
                int ellipsisPos = pos;

                if (trimmed.charAt(pos) == '*') {
                    charCount = Integer.MAX_VALUE;
                    ellipsisPos++;
                } else {
                    if ((trimmed.charAt(pos) >= '0') && (trimmed.charAt(pos) <= '9')) {
                        charCount = trimmed.charAt(pos) - '0';
                        ellipsisPos++;
                    } else {
                        charCount = 0;
                    }
                }

                ellipsis = '\0';

                if (ellipsisPos < trimmed.length()) {
                    ellipsis = trimmed.charAt(ellipsisPos);

                    if (ellipsis == '.') {
                        ellipsis = '\0';
                    }
                }

                fragments.add(new PatternAbbreviatorFragment(charCount, ellipsis));
                pos = trimmed.indexOf(".", pos);

                if (pos == -1) {
                    break;
                }

                pos++;
            }

            return new PatternAbbreviator(fragments);
        }

        //
        //  no matching abbreviation, return defaultAbbreviator
        //
        return DEFAULT;
    }

    /**
     * Gets default abbreviator.
     *
     * @return default abbreviator.
     */
    public static NameAbbreviator getDefaultAbbreviator() {
        return DEFAULT;
    }

    /**
     * Abbreviates a name in a String.
     *
     * @param buf       buffer, may not be null.
     * @return The abbreviated String.
     */
    public abstract String abbreviate(final String buf);

    /**
     * Abbreviator that simply appends full name to buffer.
     */
    private static class NOPAbbreviator extends NameAbbreviator {
        /**
         * Constructor.
         */
        public NOPAbbreviator() {
        }

        /**
         * {@inheritDoc}
         */
        public String abbreviate(final String buf) {
            return buf;
        }
    }

    /**
     * Abbreviator that drops starting path elements.
     */
    private static class MaxElementAbbreviator extends NameAbbreviator {
        /**
         * Maximum number of path elements to output.
         */
        private final int count;

        /**
         * Create new instance.
         *
         * @param count maximum number of path elements to output.
         */
        public MaxElementAbbreviator(final int count) {
            this.count = count < 1 ? 1 : count;
        }

        /**
         * Abbreviate name.
         *
         * @param buf The String to abbreviate.
         * @return the abbreviated String.
         */
        public String abbreviate(final String buf) {

            // We substract 1 from 'len' when assigning to 'end' to avoid out of
            // bounds exception in return r.substring(end+1, len). This can happen if
            // precision is 1 and the category name ends with a dot.
            int end = buf.length() - 1;

            for (int i = count; i > 0; i--) {
                end = buf.lastIndexOf(".", end - 1);
                if (end == -1) {
                    return buf;
                }
            }

            return buf.substring(end + 1);
        }
    }

    /**
     * Fragment of an pattern abbreviator.
     */
    private static class PatternAbbreviatorFragment {
        /**
         * Count of initial characters of element to output.
         */
        private final int charCount;

        /**
         * Character used to represent dropped characters.
         * '\0' indicates no representation of dropped characters.
         */
        private final char ellipsis;

        /**
         * Creates a PatternAbbreviatorFragment.
         *
         * @param charCount number of initial characters to preserve.
         * @param ellipsis  character to represent elimination of characters,
         *                  '\0' if no ellipsis is desired.
         */
        public PatternAbbreviatorFragment(
            final int charCount, final char ellipsis) {
            this.charCount = charCount;
            this.ellipsis = ellipsis;
        }

        /**
         * Abbreviate element of name.
         *
         * @param buf      buffer to receive element.
         * @param startPos starting index of name element.
         * @return starting index of next element.
         */
        public int abbreviate(final StringBuilder buf, final int startPos) {
            int nextDot = buf.toString().indexOf(".", startPos);

            if (nextDot != -1) {
                if ((nextDot - startPos) > charCount) {
                    buf.delete(startPos + charCount, nextDot);
                    nextDot = startPos + charCount;

                    if (ellipsis != '\0') {
                        buf.insert(nextDot, ellipsis);
                        nextDot++;
                    }
                }

                nextDot++;
            }

            return nextDot;
        }
    }

    /**
     * Pattern abbreviator.
     */
    private static class PatternAbbreviator extends NameAbbreviator {
        /**
         * Element abbreviation patterns.
         */
        private final PatternAbbreviatorFragment[] fragments;

        /**
         * Create PatternAbbreviator.
         *
         * @param fragments element abbreviation patterns.
         */
        public PatternAbbreviator(List fragments) {
            if (fragments.size() == 0) {
                throw new IllegalArgumentException(
                    "fragments must have at least one element");
            }

            this.fragments = new PatternAbbreviatorFragment[fragments.size()];
            fragments.toArray(this.fragments);
        }

        /**
         * Abbreviate name.
         *
         * @param buf       buffer that abbreviated name is appended.
         * @param nameStart start of name.
         */
        public String abbreviate(final String buf) {
            //
            //  all non-terminal patterns are executed once
            //
            int pos = 0;
            StringBuilder sb = new StringBuilder(buf);

            for (int i = 0; (i < (fragments.length - 1)) && (pos < buf.length());
                 i++) {
                pos = fragments[i].abbreviate(sb, pos);
            }

            //
            //   last pattern in executed repeatedly
            //
            PatternAbbreviatorFragment terminalFragment = fragments[fragments.length - 1];

            while ((pos < buf.length()) && (pos >= 0)) {
                pos = terminalFragment.abbreviate(sb, pos);
            }
            return sb.toString();
        }
    }
}