Update #0 - First Release

sources/main/java/com/google/common/escape/ArrayBasedUnicodeEscaper.java

@@ -0,0 +1,212 @@
+/*
+ * 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 java.util.Map;
+
+import javax.annotation.Nullable;
+
+import com.google.common.annotations.Beta;
+import com.google.common.annotations.GwtCompatible;
+
+/**
+ * A {@link UnicodeEscaper} that uses an array to quickly look up replacement
+ * characters for a given code point. An additional safe range is provided that
+ * determines whether code points 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 HTML escaping where the
+ * replacement array contains information about the named HTML entities such as
+ * {@code &amp;} and {@code &quot;} while {@link #escapeUnsafe} is overridden to
+ * handle general escaping of the form {@code &#NNNNN;}.
+ *
+ * <p>
+ * The size of the data structure used by {@link ArrayBasedUnicodeEscaper} is
+ * proportional to the highest valued code point 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 David Beaumont
+ * @since 15.0
+ */
+@Beta
+@GwtCompatible
+public abstract class ArrayBasedUnicodeEscaper extends UnicodeEscaper {
+	// The replacement array (see ArrayBasedEscaperMap).
+	private final char[][] replacements;
+	// The number of elements in the replacement array.
+	private final int replacementsLength;
+	// The first code point in the safe range.
+	private final int safeMin;
+	// The last code point in the safe range.
+	private final int safeMax;
+
+	// Cropped values used in the fast path range checks.
+	private final char safeMinChar;
+	private final char safeMaxChar;
+
+	/**
+	 * Creates a new ArrayBasedUnicodeEscaper instance with the given replacement
+	 * map and specified safe range. If {@code safeMax < safeMin} then no code
+	 * points are considered safe.
+	 *
+	 * <p>
+	 * If a code point 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
+	 * @param unsafeReplacement the default replacement for unsafe characters or
+	 *                          null if no default replacement is required
+	 */
+	protected ArrayBasedUnicodeEscaper(Map<Character, String> replacementMap, int safeMin, int safeMax,
+			@Nullable String unsafeReplacement) {
+
+		this(ArrayBasedEscaperMap.create(replacementMap), safeMin, safeMax, unsafeReplacement);
+	}
+
+	/**
+	 * Creates a new ArrayBasedUnicodeEscaper instance with the given replacement
+	 * map and specified safe range. If {@code safeMax < safeMin} then no code
+	 * points 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 code point 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 map of replacements
+	 * @param safeMin           the lowest character value in the safe range
+	 * @param safeMax           the highest character value in the safe range
+	 * @param unsafeReplacement the default replacement for unsafe characters or
+	 *                          null if no default replacement is required
+	 */
+	protected ArrayBasedUnicodeEscaper(ArrayBasedEscaperMap escaperMap, int safeMin, int safeMax,
+			@Nullable String unsafeReplacement) {
+
+		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 fail.
+			safeMax = -1;
+			safeMin = Integer.MAX_VALUE;
+		}
+		this.safeMin = safeMin;
+		this.safeMax = safeMax;
+
+		// This is a bit of a hack but lets us do quicker per-character checks in
+		// the fast path code. The safe min/max values are very unlikely to extend
+		// into the range of surrogate characters, but if they do we must not test
+		// any values in that range. To see why, consider the case where:
+		// safeMin <= {hi,lo} <= safeMax
+		// where {hi,lo} are characters forming a surrogate pair such that:
+		// codePointOf(hi, lo) > safeMax
+		// which would result in the surrogate pair being (wrongly) considered safe.
+		// If we clip the safe range used during the per-character tests so it is
+		// below the values of characters in surrogate pairs, this cannot occur.
+		// This approach does mean that we break out of the fast path code in cases
+		// where we don't strictly need to, but this situation will almost never
+		// occur in practice.
+		if (safeMin >= Character.MIN_HIGH_SURROGATE) {
+			// The safe range is empty or the all safe code points lie in or above the
+			// surrogate range. Either way the character range is empty.
+			this.safeMinChar = Character.MAX_VALUE;
+			this.safeMaxChar = 0;
+		} else {
+			// The safe range is non empty and contains values below the surrogate
+			// range but may extend above it. We may need to clip the maximum value.
+			this.safeMinChar = (char) safeMin;
+			this.safeMaxChar = (char) Math.min(safeMax, Character.MIN_HIGH_SURROGATE - 1);
+		}
+	}
+
+	/*
+	 * 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 > safeMaxChar || c < safeMinChar) {
+				return escapeSlow(s, i);
+			}
+		}
+		return s;
+	}
+
+	/* Overridden for performance. */
+	@Override
+	protected final int nextEscapeIndex(CharSequence csq, int index, int end) {
+		while (index < end) {
+			char c = csq.charAt(index);
+			if ((c < replacementsLength && replacements[c] != null) || c > safeMaxChar || c < safeMinChar) {
+				break;
+			}
+			index++;
+		}
+		return index;
+	}
+
+	/**
+	 * Escapes a single Unicode code point 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(int cp) {
+		if (cp < replacementsLength) {
+			char[] chars = replacements[cp];
+			if (chars != null) {
+				return chars;
+			}
+		}
+		if (cp >= safeMin && cp <= safeMax) {
+			return null;
+		}
+		return escapeUnsafe(cp);
+	}
+
+	/**
+	 * Escapes a code point 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 code points if required.
+	 *
+	 * <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 cp the Unicode code point to escape
+	 * @return the replacement characters, or {@code null} if no escaping was
+	 *         required
+	 */
+	protected abstract char[] escapeUnsafe(int cp);
+}