1 /*
2 * Copyright (C) 2009 The Guava Authors
3 *
4 * Licensed under the Apache License, Version 2.0 (the "License");
5 * you may not use this file except in compliance with the License.
6 * You may obtain a copy of the License at
7 *
8 * http://www.apache.org/licenses/LICENSE-2.0
9 *
10 * Unless required by applicable law or agreed to in writing, software
11 * distributed under the License is distributed on an "AS IS" BASIS,
12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13 * See the License for the specific language governing permissions and
14 * limitations under the License.
15 */
16
17 package com.google.common.escape;
18
19 import static com.google.common.base.Preconditions.checkNotNull;
20
21 import com.google.common.annotations.Beta;
22 import com.google.common.annotations.GwtCompatible;
23 import com.google.common.annotations.VisibleForTesting;
24
25 import java.util.Collections;
26 import java.util.Map;
27
28 /**
29 * An implementation-specific parameter class suitable for initializing
30 * {@link ArrayBasedCharEscaper} or {@link ArrayBasedUnicodeEscaper} instances.
31 * This class should be used when more than one escaper is created using the
32 * same character replacement mapping to allow the underlying (implementation
33 * specific) data structures to be shared.
34 *
35 * <p>The size of the data structure used by ArrayBasedCharEscaper and
36 * ArrayBasedUnicodeEscaper is proportional to the highest valued character that
37 * has a replacement. For example a replacement map containing the single
38 * character '{@literal \}u1000' will require approximately 16K of memory.
39 * As such sharing this data structure between escaper instances is the primary
40 * goal of this class.
41 *
42 * @author David Beaumont
43 * @since 15.0
44 */
45 @Beta
46 @GwtCompatible
47 public final class ArrayBasedEscaperMap {
48 /**
49 * Returns a new ArrayBasedEscaperMap for creating ArrayBasedCharEscaper or
50 * ArrayBasedUnicodeEscaper instances.
51 *
52 * @param replacements a map of characters to their escaped representations
53 */
54 public static ArrayBasedEscaperMap create(
55 Map<Character, String> replacements) {
56 return new ArrayBasedEscaperMap(createReplacementArray(replacements));
57 }
58
59 // The underlying replacement array we can share between multiple escaper
60 // instances.
61 private final char[][] replacementArray;
62
63 private ArrayBasedEscaperMap(char[][] replacementArray) {
64 this.replacementArray = replacementArray;
65 }
66
67 // Returns the non-null array of replacements for fast lookup.
68 char[][] getReplacementArray() {
69 return replacementArray;
70 }
71
72 // Creates a replacement array from the given map. The returned array is a
73 // linear lookup table of replacement character sequences indexed by the
74 // original character value.
75 @VisibleForTesting
76 static char[][] createReplacementArray(Map<Character, String> map) {
77 checkNotNull(map); // GWT specific check (do not optimize)
78 if (map.isEmpty()) {
79 return EMPTY_REPLACEMENT_ARRAY;
80 }
81 char max = Collections.max(map.keySet());
82 char[][] replacements = new char[max + 1][];
83 for (char c : map.keySet()) {
84 replacements[c] = map.get(c).toCharArray();
85 }
86 return replacements;
87 }
88
89 // Immutable empty array for when there are no replacements.
90 private static final char[][] EMPTY_REPLACEMENT_ARRAY = new char[0][0];
91 }