https://github.com/google/guava/guava: Guava is a suite of core and expanded libraries that include utility classes, google's collections, io classes, and much much more. 
/*
 * 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 CharEscaper that uses an array to quickly look up replacement characters for a given char value. An additional safe range is provided that determines whether 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 \\t and \\n while escapeUnsafe is overridden to handle general escaping of the form \\uxxxx. 
The size of the data structure used by ArrayBasedCharEscaper is proportional to the highest valued character that requires escaping. For example a replacement map containing the single character '\u1000' will require approximately 16K of memory. If you need to create multiple escaper instances that have the same character replacement mapping consider using ArrayBasedEscaperMap. 
Author:Sven Mawson, David Beaumont
Since:15.0
/**
 * 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.
 *
 * <p>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}.
 *
 * <p>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 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 escapeUnsafe is called, otherwise no escaping is performed. 
Params:
  • replacementMap – a map of characters to their escaped representations
  • safeMin – the lowest character value in the safe range
  • safeMax – the highest character value in the safe range
/**
   * Creates a new ArrayBasedCharEscaper instance with the given replacement map and specified safe
   * range. If {@code safeMax < safeMin} then no characters are considered safe.
   *
   * <p>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<Character, String> 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 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 escapeUnsafe is called, otherwise no escaping is performed. 
Params:
  • escaperMap – the mapping of characters to be escaped
  • safeMin – the lowest character value in the safe range
  • safeMax – the highest character value in the safe range
/**
   * 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.
   *
   * <p>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 escapeUnsafe is called. 
/**
   * 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 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).

Params:
  • c – the character to escape
Returns:the replacement characters, or null if no escaping was required
/**
   * 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.
   *
   * <p>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);
}