com.facebook.presto.jdbc.internal.guava.escape.ArrayBasedCharEscaper Maven / Gradle / Ivy
/*
* 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.facebook.presto.jdbc.internal.guava.escape;
import static com.facebook.presto.jdbc.internal.guava.base.Preconditions.checkNotNull;
import com.facebook.presto.jdbc.internal.guava.annotations.Beta;
import com.facebook.presto.jdbc.internal.guava.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(dbeaumont,cpovirk): Rename this something better once refactoring done
protected abstract char[] escapeUnsafe(char c);
}