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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.verifier;
18  
19  import java.util.HashMap;
20  import java.util.List;
21  import java.util.Map;
22  import java.util.Vector;
23  
24  /**
25   * This class produces instances of the Verifier class. Its purpose is to make sure that they are singleton instances
26   * with respect to the class name they operate on. That means, for every class (represented by a unique fully qualified
27   * class name) there is exactly one Verifier.
28   *
29   * @see Verifier
30   */
31  public class VerifierFactory {
32  
33      /**
34       * The HashMap that holds the data about the already-constructed Verifier instances.
35       */
36      private static final Map<String, Verifier> MAP = new HashMap<>();
37  
38      /**
39       * The VerifierFactoryObserver instances that observe the VerifierFactory.
40       */
41      private static final List<VerifierFactoryObserver> OBSVERVERS = new Vector<>();
42  
43      /**
44       * Adds the VerifierFactoryObserver o to the list of observers.
45       */
46      public static void attach(final VerifierFactoryObserver o) {
47          OBSVERVERS.add(o);
48      }
49  
50      /**
51       * Clears the factory.
52       *
53       * @since 6.6.2
54       */
55      public static void clear() {
56          MAP.clear();
57          OBSVERVERS.clear();
58      }
59  
60      /**
61       * Removes the VerifierFactoryObserver o from the list of observers.
62       */
63      public static void detach(final VerifierFactoryObserver o) {
64          OBSVERVERS.remove(o);
65      }
66  
67      /**
68       * Returns the (only) verifier responsible for the class with the given name. Possibly a new Verifier object is
69       * transparently created.
70       *
71       * @return the (only) verifier responsible for the class with the given name.
72       */
73      public static Verifier getVerifier(final String fullyQualifiedClassName) {
74          return MAP.computeIfAbsent(fullyQualifiedClassName, k -> {
75              final Verifier v = new Verifier(k);
76              notify(k);
77              return v;
78          });
79      }
80  
81      /**
82       * Returns all Verifier instances created so far. This is useful when a Verifier recursively lets the VerifierFactory
83       * create other Verifier instances and if you want to verify the transitive hull of referenced class files.
84       */
85      public static Verifier[] getVerifiers() {
86          return MAP.values().toArray(Verifier.EMPTY_ARRAY);
87      }
88  
89      /**
90       * Notifies the observers of a newly generated Verifier.
91       */
92      private static void notify(final String fullyQualifiedClassName) {
93          // notify the observers
94          OBSVERVERS.forEach(vfo -> vfo.update(fullyQualifiedClassName));
95      }
96  
97      /**
98       * The VerifierFactory is not instantiable.
99       */
100     private VerifierFactory() {
101     }
102 }