com.google.common.escape.Escapers 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.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.HashMap;
import java.util.Map;
import javax.annotation.Nullable;
/**
* Static utility methods pertaining to {@link Escaper} instances.
*
* @author Sven Mawson
* @author David Beaumont
* @since 15.0
*/
@Beta
@GwtCompatible
public final class Escapers {
private Escapers() {}
/**
* Returns an {@link Escaper} that does no escaping, passing all character
* data through unchanged.
*/
public static Escaper nullEscaper() {
return NULL_ESCAPER;
}
// An Escaper that efficiently performs no escaping.
// Extending CharEscaper (instead of Escaper) makes Escapers.compose() easier.
private static final Escaper NULL_ESCAPER = new CharEscaper() {
@Override public String escape(String string) {
return checkNotNull(string);
}
@Override protected char[] escape(char c) {
// TODO: Fix tests not to call this directly and make it throw an error.
return null;
}
};
/**
* Returns a builder for creating simple, fast escapers. A builder instance
* can be reused and each escaper that is created will be a snapshot of the
* current builder state. Builders are not thread safe.
*
* The initial state of the builder is such that:
*
* - There are no replacement mappings
-
*
- {@code safeMin == Character.MIN_VALUE}
* - {@code safeMax == Character.MAX_VALUE}
* - {@code unsafeReplacement == null}
*
* For performance reasons escapers created by this builder are not
* Unicode aware and will not validate the well-formedness of their input.
*/
public static Builder builder() {
return new Builder();
}
/**
* A builder for simple, fast escapers.
*
*
Typically an escaper needs to deal with the escaping of high valued
* characters or code points. In these cases it is necessary to extend either
* {@link ArrayBasedCharEscaper} or {@link ArrayBasedUnicodeEscaper} to
* provide the desired behavior. However this builder is suitable for creating
* escapers that replace a relative small set of characters.
*
* @author David Beaumont
* @since 15.0
*/
@Beta
public static final class Builder {
private final Map replacementMap =
new HashMap();
private char safeMin = Character.MIN_VALUE;
private char safeMax = Character.MAX_VALUE;
private String unsafeReplacement = null;
// The constructor is exposed via the builder() method above.
private Builder() {}
/**
* Sets the safe range of characters for the escaper. Characters in this
* range that have no explicit replacement are considered 'safe' and remain
* unescaped in the output. If {@code safeMax < safeMin} then the safe range
* is empty.
*
* @param safeMin the lowest 'safe' character
* @param safeMax the highest 'safe' character
* @return the builder instance
*/
public Builder setSafeRange(char safeMin, char safeMax) {
this.safeMin = safeMin;
this.safeMax = safeMax;
return this;
}
/**
* Sets the replacement string for any characters outside the 'safe' range
* that have no explicit replacement. If {@code unsafeReplacement} is
* {@code null} then no replacement will occur, if it is {@code ""} then
* the unsafe characters are removed from the output.
*
* @param unsafeReplacement the string to replace unsafe chracters
* @return the builder instance
*/
public Builder setUnsafeReplacement(@Nullable String unsafeReplacement) {
this.unsafeReplacement = unsafeReplacement;
return this;
}
/**
* Adds a replacement string for the given input character. The specified
* character will be replaced by the given string whenever it occurs in the
* input, irrespective of whether it lies inside or outside the 'safe'
* range.
*
* @param c the character to be replaced
* @param replacement the string to replace the given character
* @return the builder instance
* @throws NullPointerException if {@code replacement} is null
*/
public Builder addEscape(char c, String replacement) {
checkNotNull(replacement);
// This can replace an existing character (the builder is re-usable).
replacementMap.put(c, replacement);
return this;
}
/**
* Returns a new escaper based on the current state of the builder.
*/
public Escaper build() {
return new ArrayBasedCharEscaper(replacementMap, safeMin, safeMax) {
private final char[] replacementChars =
unsafeReplacement != null ? unsafeReplacement.toCharArray() : null;
@Override protected char[] escapeUnsafe(char c) {
return replacementChars;
}
};
}
}
/**
* Returns a {@link UnicodeEscaper} equivalent to the given escaper instance.
* If the escaper is already a UnicodeEscaper then it is simply returned,
* otherwise it is wrapped in a UnicodeEscaper.
*
* When a {@link CharEscaper} escaper is wrapped by this method it acquires
* extra behavior with respect to the well-formedness of Unicode character
* sequences and will throw {@link IllegalArgumentException} when given bad
* input.
*
* @param escaper the instance to be wrapped
* @return a UnicodeEscaper with the same behavior as the given instance
* @throws NullPointerException if escaper is null
* @throws IllegalArgumentException if escaper is not a UnicodeEscaper or a
* CharEscaper
*/
static UnicodeEscaper asUnicodeEscaper(Escaper escaper) {
checkNotNull(escaper);
if (escaper instanceof UnicodeEscaper) {
return (UnicodeEscaper) escaper;
} else if (escaper instanceof CharEscaper) {
return wrap((CharEscaper) escaper);
}
// In practice this shouldn't happen because it would be very odd not to
// extend either CharEscaper or UnicodeEscaper for non trivial cases.
throw new IllegalArgumentException("Cannot create a UnicodeEscaper from: " +
escaper.getClass().getName());
}
/**
* Returns a string that would replace the given character in the specified
* escaper, or {@code null} if no replacement should be made. This method is
* intended for use in tests through the {@code EscaperAsserts} class;
* production users of {@link CharEscaper} should limit themselves to its
* public interface.
*
* @param c the character to escape if necessary
* @return the replacement string, or {@code null} if no escaping was needed
*/
public static String computeReplacement(CharEscaper escaper, char c) {
return stringOrNull(escaper.escape(c));
}
/**
* Returns a string that would replace the given character in the specified
* escaper, or {@code null} if no replacement should be made. This method is
* intended for use in tests through the {@code EscaperAsserts} class;
* production users of {@link UnicodeEscaper} should limit themselves to its
* public interface.
*
* @param cp the Unicode code point to escape if necessary
* @return the replacement string, or {@code null} if no escaping was needed
*/
public static String computeReplacement(UnicodeEscaper escaper, int cp) {
return stringOrNull(escaper.escape(cp));
}
private static String stringOrNull(char[] in) {
return (in == null) ? null : new String(in);
}
/** Private helper to wrap a CharEscaper as a UnicodeEscaper. */
private static UnicodeEscaper wrap(final CharEscaper escaper) {
return new UnicodeEscaper() {
@Override protected char[] escape(int cp) {
// If a code point maps to a single character, just escape that.
if (cp < Character.MIN_SUPPLEMENTARY_CODE_POINT) {
return escaper.escape((char) cp);
}
// Convert the code point to a surrogate pair and escape them both.
// Note: This code path is horribly slow and typically allocates 4 new
// char[] each time it is invoked. However this avoids any
// synchronization issues and makes the escaper thread safe.
char[] surrogateChars = new char[2];
Character.toChars(cp, surrogateChars, 0);
char[] hiChars = escaper.escape(surrogateChars[0]);
char[] loChars = escaper.escape(surrogateChars[1]);
// If either hiChars or lowChars are non-null, the CharEscaper is trying
// to escape the characters of a surrogate pair separately. This is
// uncommon and applies only to escapers that assume UCS-2 rather than
// UTF-16. See: http://en.wikipedia.org/wiki/UTF-16/UCS-2
if (hiChars == null && loChars == null) {
// We expect this to be the common code path for most escapers.
return null;
}
// Combine the characters and/or escaped sequences into a single array.
int hiCount = hiChars != null ? hiChars.length : 1;
int loCount = loChars != null ? loChars.length : 1;
char[] output = new char[hiCount + loCount];
if (hiChars != null) {
// TODO: Is this faster than System.arraycopy() for small arrays?
for (int n = 0; n < hiChars.length; ++n) {
output[n] = hiChars[n];
}
} else {
output[0] = surrogateChars[0];
}
if (loChars != null) {
for (int n = 0; n < loChars.length; ++n) {
output[hiCount + n] = loChars[n];
}
} else {
output[hiCount] = surrogateChars[1];
}
return output;
}
};
}
}