1 /*
2 * Licensed to the Apache Software Foundation (ASF) under one or more
3 * contributor license agreements. See the NOTICE file distributed with
4 * this work for additional information regarding copyright ownership.
5 * The ASF licenses this file to You under the Apache License, Version 2.0
6 * (the "License"); you may not use this file except in compliance with
7 * the License. You may obtain a copy of the License at
8 *
9 * http://www.apache.org/licenses/LICENSE-2.0
10 *
11 * Unless required by applicable law or agreed to in writing, software
12 * distributed under the License is distributed on an "AS IS" BASIS,
13 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
14 * See the License for the specific language governing permissions and
15 * limitations under the License.
16 */
17 package org.apache.bcel.classfile;
18
19 import java.io.DataInput;
20 import java.io.DataOutputStream;
21 import java.io.IOException;
22 import java.util.HashMap;
23 import java.util.LinkedHashMap;
24 import java.util.Map;
25 import java.util.Objects;
26
27 import org.apache.bcel.Const;
28
29 /**
30 * Extends the abstract {@link Constant} to represent a reference to a UTF-8 encoded string.
31 * <p>
32 * The following system properties govern caching this class performs.
33 * </p>
34 * <ul>
35 * <li>{@link #SYS_PROP_CACHE_MAX_ENTRIES} (since 6.4): The size of the cache, by default 0, meaning caching is
36 * disabled.</li>
37 * <li>{@link #SYS_PROP_CACHE_MAX_ENTRY_SIZE} (since 6.0): The maximum size of the values to cache, by default 200, 0
38 * disables caching. Values larger than this are <em>not</em> cached.</li>
39 * <li>{@link #SYS_PROP_STATISTICS} (since 6.0): Prints statistics on the console when the JVM exits.</li>
40 * </ul>
41 * <p>
42 * Here is a sample Maven invocation with caching disabled:
43 * </p>
44 *
45 * <pre>
46 * mvn test -Dbcel.statistics=true -Dbcel.maxcached.size=0 -Dbcel.maxcached=0
47 * </pre>
48 * <p>
49 * Here is a sample Maven invocation with caching enabled:
50 * </p>
51 *
52 * <pre>
53 * mvn test -Dbcel.statistics=true -Dbcel.maxcached.size=100000 -Dbcel.maxcached=5000000
54 * </pre>
55 *
56 * @see Constant
57 */
58 public final class ConstantUtf8 extends Constant {
59
60 private static final class Cache {
61
62 private static final boolean BCEL_STATISTICS = Boolean.getBoolean(SYS_PROP_STATISTICS);
63 private static final int MAX_ENTRIES = Integer.getInteger(SYS_PROP_CACHE_MAX_ENTRIES, 0).intValue();
64 private static final int INITIAL_CAPACITY = (int) (MAX_ENTRIES / 0.75);
65
66 private static final HashMap<String, ConstantUtf8> CACHE = new LinkedHashMap<String, ConstantUtf8>(INITIAL_CAPACITY, 0.75f, true) {
67
68 private static final long serialVersionUID = -8506975356158971766L;
69
70 @Override
71 protected boolean removeEldestEntry(final Map.Entry<String, ConstantUtf8> eldest) {
72 return size() > MAX_ENTRIES;
73 }
74 };
75
76 // Set the size to 0 or below to skip caching entirely
77 private static final int MAX_ENTRY_SIZE = Integer.getInteger(SYS_PROP_CACHE_MAX_ENTRY_SIZE, 200).intValue();
78
79 static boolean isEnabled() {
80 return Cache.MAX_ENTRIES > 0 && MAX_ENTRY_SIZE > 0;
81 }
82
83 }
84
85 // TODO these should perhaps be AtomicInt?
86 private static volatile int considered;
87 private static volatile int created;
88 private static volatile int hits;
89 private static volatile int skipped;
90
91 private static final String SYS_PROP_CACHE_MAX_ENTRIES = "bcel.maxcached";
92 private static final String SYS_PROP_CACHE_MAX_ENTRY_SIZE = "bcel.maxcached.size";
93 private static final String SYS_PROP_STATISTICS = "bcel.statistics";
94
95 static {
96 if (Cache.BCEL_STATISTICS) {
97 Runtime.getRuntime().addShutdownHook(new Thread(ConstantUtf8::printStats));
98 }
99 }
100
101 /**
102 * Clears the cache.
103 *
104 * @since 6.4.0
105 */
106 public static synchronized void clearCache() {
107 Cache.CACHE.clear();
108 }
109
110 // for access by test code
111 static synchronized void clearStats() {
112 hits = considered = skipped = created = 0;
113 }
114
115 // Avoid Spotbugs complaint about Write to static field
116 private static void countCreated() {
117 created++;
118 }
119
120 /**
121 * Gets a new or cached instance of the given value.
122 * <p>
123 * See {@link ConstantUtf8} class Javadoc for details.
124 * </p>
125 *
126 * @param value the value.
127 * @return a new or cached instance of the given value.
128 * @since 6.0
129 */
130 public static ConstantUtf8 getCachedInstance(final String value) {
131 if (value.length() > Cache.MAX_ENTRY_SIZE) {
132 skipped++;
133 return new ConstantUtf8(value);
134 }
135 considered++;
136 synchronized (ConstantUtf8.class) { // might be better with a specific lock object
137 ConstantUtf8 result = Cache.CACHE.get(value);
138 if (result != null) {
139 hits++;
140 return result;
141 }
142 result = new ConstantUtf8(value);
143 Cache.CACHE.put(value, result);
144 return result;
145 }
146 }
147
148 /**
149 * Gets a new or cached instance of the given value.
150 * <p>
151 * See {@link ConstantUtf8} class Javadoc for details.
152 * </p>
153 *
154 * @param dataInput the value.
155 * @return a new or cached instance of the given value.
156 * @throws IOException if an I/O error occurs.
157 * @since 6.0
158 */
159 public static ConstantUtf8 getInstance(final DataInput dataInput) throws IOException {
160 return getInstance(dataInput.readUTF());
161 }
162
163 /**
164 * Gets a new or cached instance of the given value.
165 * <p>
166 * See {@link ConstantUtf8} class Javadoc for details.
167 * </p>
168 *
169 * @param value the value.
170 * @return a new or cached instance of the given value.
171 * @since 6.0
172 */
173 public static ConstantUtf8 getInstance(final String value) {
174 return Cache.isEnabled() ? getCachedInstance(value) : new ConstantUtf8(value);
175 }
176
177 // for access by test code
178 static void printStats() {
179 final String prefix = "[Apache Commons BCEL]";
180 System.err.printf("%s Cache hit %,d/%,d, %d skipped.%n", prefix, hits, considered, skipped);
181 System.err.printf("%s Total of %,d ConstantUtf8 objects created.%n", prefix, created);
182 System.err.printf("%s Configuration: %s=%,d, %s=%,d.%n", prefix, SYS_PROP_CACHE_MAX_ENTRIES, Cache.MAX_ENTRIES, SYS_PROP_CACHE_MAX_ENTRY_SIZE,
183 Cache.MAX_ENTRY_SIZE);
184 }
185
186 private final String value;
187
188 /**
189 * Initializes from another object.
190 *
191 * @param constantUtf8 the value.
192 */
193 public ConstantUtf8(final ConstantUtf8 constantUtf8) {
194 this(constantUtf8.getBytes());
195 }
196
197 /**
198 * Initializes instance from file data.
199 *
200 * @param dataInput Input stream
201 * @throws IOException if an I/O error occurs.
202 */
203 ConstantUtf8(final DataInput dataInput) throws IOException {
204 super(Const.CONSTANT_Utf8);
205 value = dataInput.readUTF();
206 countCreated();
207 }
208
209 /**
210 * @param value Data
211 */
212 public ConstantUtf8(final String value) {
213 super(Const.CONSTANT_Utf8);
214 this.value = Objects.requireNonNull(value, "value");
215 countCreated();
216 }
217
218 /**
219 * Called by objects that are traversing the nodes of the tree implicitly defined by the contents of a Java class.
220 * I.e., the hierarchy of methods, fields, attributes, etc. spawns a tree of objects.
221 *
222 * @param v Visitor object
223 */
224 @Override
225 public void accept(final Visitor v) {
226 v.visitConstantUtf8(this);
227 }
228
229 /**
230 * Dumps String in Utf8 format to file stream.
231 *
232 * @param file Output file stream
233 * @throws IOException if an I/O error occurs.
234 */
235 @Override
236 public void dump(final DataOutputStream file) throws IOException {
237 file.writeByte(super.getTag());
238 file.writeUTF(value);
239 }
240
241 /**
242 * @return Data converted to string.
243 */
244 public String getBytes() {
245 return value;
246 }
247
248 /**
249 * @param bytes the raw bytes of this UTF-8
250 * @deprecated (since 6.0)
251 */
252 @java.lang.Deprecated
253 public void setBytes(final String bytes) {
254 throw new UnsupportedOperationException();
255 }
256
257 /**
258 * @return String representation
259 */
260 @Override
261 public String toString() {
262 return super.toString() + "(\"" + Utility.replace(value, "\n", "\\n") + "\")";
263 }
264 }