Update #0 - First Release

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

@@ -0,0 +1,165 @@
+/*
+ * 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 com.google.common.annotations.Beta;
+import com.google.common.annotations.GwtCompatible;
+
+/**
+ * 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 {@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 {@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 {@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.
+	 *
+	 * <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);
+}