1 /*
2 * Copyright (C) 2009 The Guava Authors
3 *
4 * Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except
5 * in compliance with the License. You may obtain a copy of the License at
6 *
7 * http://www.apache.org/licenses/LICENSE-2.0
8 *
9 * Unless required by applicable law or agreed to in writing, software distributed under the License
10 * is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express
11 * or implied. See the License for the specific language governing permissions and limitations under
12 * the License.
13 */
14
15 package com.google.common.escape;
16
17 import static com.google.common.base.Preconditions.checkNotNull;
18
19 import com.google.common.annotations.Beta;
20 import com.google.common.annotations.GwtCompatible;
21 import com.google.common.annotations.VisibleForTesting;
22 import java.util.Collections;
23 import java.util.Map;
24
25 /**
26 * An implementation-specific parameter class suitable for initializing {@link
27 * ArrayBasedCharEscaper} or {@link ArrayBasedUnicodeEscaper} instances. This class should be used
28 * when more than one escaper is created using the same character replacement mapping to allow the
29 * underlying (implementation specific) data structures to be shared.
30 *
31 * <p>The size of the data structure used by ArrayBasedCharEscaper and ArrayBasedUnicodeEscaper is
32 * proportional to the highest valued character that has a replacement. For example a replacement
33 * map containing the single character '{@literal \}u1000' will require approximately 16K of memory.
34 * As such sharing this data structure between escaper instances is the primary goal of this class.
35 *
36 * @author David Beaumont
37 * @since 15.0
38 */
39 @Beta
40 @GwtCompatible
41 @ElementTypesAreNonnullByDefault
42 public final class ArrayBasedEscaperMap {
43 /**
44 * Returns a new ArrayBasedEscaperMap for creating ArrayBasedCharEscaper or
45 * ArrayBasedUnicodeEscaper instances.
46 *
47 * @param replacements a map of characters to their escaped representations
48 */
49 public static ArrayBasedEscaperMap create(Map<Character, String> replacements) {
50 return new ArrayBasedEscaperMap(createReplacementArray(replacements));
51 }
52
53 // The underlying replacement array we can share between multiple escaper
54 // instances.
55 private final char[][] replacementArray;
56
57 private ArrayBasedEscaperMap(char[][] replacementArray) {
58 this.replacementArray = replacementArray;
59 }
60
61 // Returns the non-null array of replacements for fast lookup.
62 char[][] getReplacementArray() {
63 return replacementArray;
64 }
65
66 // Creates a replacement array from the given map. The returned array is a
67 // linear lookup table of replacement character sequences indexed by the
68 // original character value.
69 @VisibleForTesting
70 static char[][] createReplacementArray(Map<Character, String> map) {
71 checkNotNull(map); // GWT specific check (do not optimize)
72 if (map.isEmpty()) {
73 return EMPTY_REPLACEMENT_ARRAY;
74 }
75 char max = Collections.max(map.keySet());
76 char[][] replacements = new char[max + 1][];
77 for (Character c : map.keySet()) {
78 replacements[c] = map.get(c).toCharArray();
79 }
80 return replacements;
81 }
82
83 // Immutable empty array for when there are no replacements.
84 private static final char[][] EMPTY_REPLACEMENT_ARRAY = new char[0][0];
85 }