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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 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 }