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/*
 * Copyright (C) 2009 The Guava Authors
 *
 * Licensed 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 com.google.common.escape;

import static com.google.common.base.Preconditions.checkNotNull;

import com.google.common.annotations.Beta;
import com.google.common.annotations.GwtCompatible;

import java.util.Map;

/**
 * A {@link CharEscaper} that uses an array to quickly look up replacement
 * characters for a given {@code char} value. An additional safe range is
 * provided that determines whether {@code char} values without specific
 * replacements are to be considered safe and left unescaped or should be
 * escaped in a general way.
 *
 * 

A good example of usage of this class is for Java source code escaping * where the replacement array contains information about special ASCII * characters such as {@code \\t} and {@code \\n} while {@link #escapeUnsafe} * is overridden to handle general escaping of the form {@code \\uxxxx}. * *

The size of the data structure used by {@link ArrayBasedCharEscaper} is * proportional to the highest valued character that requires escaping. * For example a replacement map containing the single character * '{@code \}{@code u1000}' will require approximately 16K of memory. If you * need to create multiple escaper instances that have the same character * replacement mapping consider using {@link ArrayBasedEscaperMap}. * * @author Sven Mawson * @author David Beaumont * @since 15.0 */ @Beta @GwtCompatible public abstract class ArrayBasedCharEscaper extends CharEscaper { // The replacement array (see ArrayBasedEscaperMap). private final char[][] replacements; // The number of elements in the replacement array. private final int replacementsLength; // The first character in the safe range. private final char safeMin; // The last character in the safe range. private final char safeMax; /** * Creates a new ArrayBasedCharEscaper instance with the given replacement map * and specified safe range. If {@code safeMax < safeMin} then no characters * are considered safe. * *

If a character has no mapped replacement then it is checked against the * safe range. If it lies outside that, then {@link #escapeUnsafe} is * called, otherwise no escaping is performed. * * @param replacementMap a map of characters to their escaped representations * @param safeMin the lowest character value in the safe range * @param safeMax the highest character value in the safe range */ protected ArrayBasedCharEscaper(Map replacementMap, char safeMin, char safeMax) { this(ArrayBasedEscaperMap.create(replacementMap), safeMin, safeMax); } /** * Creates a new ArrayBasedCharEscaper instance with the given replacement map * and specified safe range. If {@code safeMax < safeMin} then no characters * are considered safe. This initializer is useful when explicit instances of * ArrayBasedEscaperMap are used to allow the sharing of large replacement * mappings. * *

If a character has no mapped replacement then it is checked against the * safe range. If it lies outside that, then {@link #escapeUnsafe} is * called, otherwise no escaping is performed. * * @param escaperMap the mapping of characters to be escaped * @param safeMin the lowest character value in the safe range * @param safeMax the highest character value in the safe range */ protected ArrayBasedCharEscaper(ArrayBasedEscaperMap escaperMap, char safeMin, char safeMax) { checkNotNull(escaperMap); // GWT specific check (do not optimize) this.replacements = escaperMap.getReplacementArray(); this.replacementsLength = replacements.length; if (safeMax < safeMin) { // If the safe range is empty, set the range limits to opposite extremes // to ensure the first test of either value will (almost certainly) fail. safeMax = Character.MIN_VALUE; safeMin = Character.MAX_VALUE; } this.safeMin = safeMin; this.safeMax = safeMax; } /* * This is overridden to improve performance. Rough benchmarking shows that * this almost doubles the speed when processing strings that do not require * any escaping. */ @Override public final String escape(String s) { checkNotNull(s); // GWT specific check (do not optimize). for (int i = 0; i < s.length(); i++) { char c = s.charAt(i); if ((c < replacementsLength && replacements[c] != null) || c > safeMax || c < safeMin) { return escapeSlow(s, i); } } return s; } /** * Escapes a single character using the replacement array and safe range * values. If the given character does not have an explicit replacement and * lies outside the safe range then {@link #escapeUnsafe} is called. */ @Override protected final char[] escape(char c) { if (c < replacementsLength) { char[] chars = replacements[c]; if (chars != null) { return chars; } } if (c >= safeMin && c <= safeMax) { return null; } return escapeUnsafe(c); } /** * Escapes a {@code char} value that has no direct explicit value in the * replacement array and lies outside the stated safe range. Subclasses should * override this method to provide generalized escaping for characters. * *

Note that arrays returned by this method must not be modified once they * have been returned. However it is acceptable to return the same array * multiple times (even for different input characters). * * @param c the character to escape * @return the replacement characters, or {@code null} if no escaping was * required */ // TODO(user,cpovirk): Rename this something better once refactoring done protected abstract char[] escapeUnsafe(char c); }





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