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    */
create( Map<Character, String> replacements)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 
ArrayBasedEscaperMap(char[][] replacementArray)63   private ArrayBasedEscaperMap(char[][] replacementArray) {
64     this.replacementArray = replacementArray;
65   }
66 
67   // Returns the non-null array of replacements for fast lookup.
getReplacementArray()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
createReplacementArray(Map<Character, String> map)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 }
92