001/*
002 * Licensed to the Apache Software Foundation (ASF) under one or more
003 * contributor license agreements.  See the NOTICE file distributed with
004 * this work for additional information regarding copyright ownership.
005 * The ASF licenses this file to You under the Apache License, Version 2.0
006 * (the "License"); you may not use this file except in compliance with
007 * the License.  You may obtain a copy of the License at
008 *
009 *      http://www.apache.org/licenses/LICENSE-2.0
010 *
011 *  Unless required by applicable law or agreed to in writing, software
012 *  distributed under the License is distributed on an "AS IS" BASIS,
013 *  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
014 *  See the License for the specific language governing permissions and
015 *  limitations under the License.
016 */
017package org.apache.bcel.verifier;
018
019import java.util.HashMap;
020import java.util.List;
021import java.util.Map;
022import java.util.Vector;
023
024/**
025 * This class produces instances of the Verifier class. Its purpose is to make sure that they are singleton instances
026 * with respect to the class name they operate on. That means, for every class (represented by a unique fully qualified
027 * class name) there is exactly one Verifier.
028 *
029 * @see Verifier
030 */
031public class VerifierFactory {
032
033    /**
034     * The HashMap that holds the data about the already-constructed Verifier instances.
035     */
036    private static final Map<String, Verifier> MAP = new HashMap<>();
037
038    /**
039     * The VerifierFactoryObserver instances that observe the VerifierFactory.
040     */
041    private static final List<VerifierFactoryObserver> OBSVERVERS = new Vector<>();
042
043    /**
044     * Adds the VerifierFactoryObserver o to the list of observers.
045     */
046    public static void attach(final VerifierFactoryObserver o) {
047        OBSVERVERS.add(o);
048    }
049
050    /**
051     * Clears the factory.
052     */
053    static void clear() {
054        MAP.clear();
055        OBSVERVERS.clear();
056    }
057
058    /**
059     * Removes the VerifierFactoryObserver o from the list of observers.
060     */
061    public static void detach(final VerifierFactoryObserver o) {
062        OBSVERVERS.remove(o);
063    }
064
065    /**
066     * Returns the (only) verifier responsible for the class with the given name. Possibly a new Verifier object is
067     * transparently created.
068     *
069     * @return the (only) verifier responsible for the class with the given name.
070     */
071    public static Verifier getVerifier(final String fullyQualifiedClassName) {
072        return MAP.computeIfAbsent(fullyQualifiedClassName, k -> {
073            final Verifier v = new Verifier(k);
074            notify(k);
075            return v;
076        });
077    }
078
079    /**
080     * Returns all Verifier instances created so far. This is useful when a Verifier recursively lets the VerifierFactory
081     * create other Verifier instances and if you want to verify the transitive hull of referenced class files.
082     */
083    public static Verifier[] getVerifiers() {
084        return MAP.values().toArray(Verifier.EMPTY_ARRAY);
085    }
086
087    /**
088     * Notifies the observers of a newly generated Verifier.
089     */
090    private static void notify(final String fullyQualifiedClassName) {
091        // notify the observers
092        OBSVERVERS.forEach(vfo -> vfo.update(fullyQualifiedClassName));
093    }
094
095    /**
096     * The VerifierFactory is not instantiable.
097     */
098    private VerifierFactory() {
099    }
100}