1 /*
2 * #%L
3 * StringEncoder.java - mongodb-async-driver - Allanbank Consulting, Inc.
4 * %%
5 * Copyright (C) 2011 - 2014 Allanbank Consulting, Inc.
6 * %%
7 * Licensed under the Apache License, Version 2.0 (the "License");
8 * you may not use this file except in compliance with the License.
9 * You may obtain a copy of the License at
10 *
11 * http://www.apache.org/licenses/LICENSE-2.0
12 *
13 * Unless required by applicable law or agreed to in writing, software
14 * distributed under the License is distributed on an "AS IS" BASIS,
15 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
16 * See the License for the specific language governing permissions and
17 * limitations under the License.
18 * #L%
19 */
20
21 package com.allanbank.mongodb.bson.io;
22
23 import java.util.Collections;
24 import java.util.HashMap;
25 import java.util.List;
26 import java.util.Map;
27 import java.util.SortedMap;
28
29 /**
30 * StringEncoderCache provides the ability to cache the encoding of a string to
31 * speed the writing of strings.
32 * <p>
33 * This class is thread safe. Thread safety is achieved by maintaining two data
34 * structures. The first is a map of seen strings to the number of times the
35 * string has been seen. The map is maintained by the base class:
36 * {@link AbstractStringCache}. The second structure is a simple map of the
37 * cached {@link String} to the encoded {@code byte[]}. The map has no locking
38 * or synchronization since it is read-only after construction.
39 * </p>
40 *
41 * @api.no This class is <b>NOT</b> part of the drivers API. This class may be
42 * mutated in incompatible ways between any two releases of the driver.
43 * @copyright 2014, Allanbank Consulting, Inc., All Rights Reserved
44 */
45 public class StringEncoderCache extends AbstractStringCache {
46
47 /** The cache of strings to bytes. */
48 private Map<String, byte[]> myCache;
49
50 /**
51 * Creates a new StringEncoder.
52 */
53 public StringEncoderCache() {
54 myCache = Collections.emptyMap();
55
56 myMaxCacheLength = DEFAULT_MAX_CACHE_LENGTH;
57 myMaxCachEntries = DEFAULT_MAX_CACHE_ENTRIES;
58 }
59
60 /**
61 * Looks in the cache for encoded bytes for the specified string.
62 *
63 * @param string
64 * The string value to find the cached bytes for.
65 * @return The cached bytes for the string. May be <code>null</code>.
66 */
67 public byte[] find(final String string) {
68 return myCache.get(string);
69 }
70
71 /**
72 * Clears the cache.
73 */
74 @Override
75 protected void clear() {
76 myCache = Collections.emptyMap();
77 super.clear();
78 }
79
80 /**
81 * Rebuilds the cache from the current collection of seen entries.
82 */
83 @Override
84 protected void rebuildCache() {
85 final SortedMap<Integer, List<SeenString>> order = buildCacheGroups();
86
87 // Rebuild the cache.
88 int count = 0;
89 final Map<String, byte[]> cache = new HashMap<String, byte[]>(
90 (int) Math.ceil(Math.min(order.size(), myMaxCachEntries) / 0.75));
91 for (final List<SeenString> seenAtCount : order.values()) {
92 for (final SeenString seen : seenAtCount) {
93 if (count < myMaxCachEntries) {
94 cache.put(seen.getValue(), seen.getBytes());
95 count += 1;
96 }
97 else {
98 mySeen.remove(seen.getValue());
99 }
100 }
101 }
102
103 myCache = cache;
104 }
105 }