    001/*
    002 * Licensed to the Apache Software Foundation (ASF) under one
    003 * or more contributor license agreements.  See the NOTICE file
    004 * distributed with this work for additional information
    005 * regarding copyright ownership.  The ASF licenses this file
    006 * to you under the Apache License, Version 2.0 (the
    007 * "License"); you may not use this file except in compliance
    008 * with the License.  You may obtain a copy of the License at
    009 *
    010 *   https://www.apache.org/licenses/LICENSE-2.0
    011 *
    012 * Unless required by applicable law or agreed to in writing,
    013 * software distributed under the License is distributed on an
    014 * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
    015 * KIND, either express or implied.  See the License for the
    016 * specific language governing permissions and limitations
    017 * under the License.
    018 */
    019package org.apache.bcel.classfile;
    020
    021import java.io.DataInput;
    022import java.io.DataOutputStream;
    023import java.io.IOException;
    024import java.util.HashMap;
    025import java.util.LinkedHashMap;
    026import java.util.Map;
    027import java.util.Objects;
    028
    029import org.apache.bcel.Const;
    030
    031/**
    032 * Extends the abstract {@link Constant} to represent a reference to a UTF-8 encoded string.
    033 * <p>
    034 * The following system properties govern caching this class performs.
    035 * </p>
    036 * <ul>
    037 * <li>{@link #SYS_PROP_CACHE_MAX_ENTRIES} (since 6.4): The size of the cache, by default 0, meaning caching is
    038 * disabled.</li>
    039 * <li>{@link #SYS_PROP_CACHE_MAX_ENTRY_SIZE} (since 6.0): The maximum size of the values to cache, by default 200, 0
    040 * disables caching. Values larger than this are <em>not</em> cached.</li>
    041 * <li>{@link #SYS_PROP_STATISTICS} (since 6.0): Prints statistics on the console when the JVM exits.</li>
    042 * </ul>
    043 * <p>
    044 * Here is a sample Maven invocation with caching disabled:
    045 * </p>
    046 *
    047 * <pre>
    048 * mvn test -Dbcel.statistics=true -Dbcel.maxcached.size=0 -Dbcel.maxcached=0
    049 * </pre>
    050 * <p>
    051 * Here is a sample Maven invocation with caching enabled:
    052 * </p>
    053 *
    054 * <pre>
    055 * mvn test -Dbcel.statistics=true -Dbcel.maxcached.size=100000 -Dbcel.maxcached=5000000
    056 * </pre>
    057 *
    058 * @see Constant
    059 */
    060public final class ConstantUtf8 extends Constant {
    061
    062    private static final class Cache {
    063
    064        private static final boolean BCEL_STATISTICS = Boolean.getBoolean(SYS_PROP_STATISTICS);
    065        private static final int MAX_ENTRIES = Integer.getInteger(SYS_PROP_CACHE_MAX_ENTRIES, 0).intValue();
    066        private static final int INITIAL_CAPACITY = (int) (MAX_ENTRIES / 0.75);
    067
    068        private static final HashMap<String, ConstantUtf8> CACHE = new LinkedHashMap<String, ConstantUtf8>(INITIAL_CAPACITY, 0.75f, true) {
    069
    070            private static final long serialVersionUID = -8506975356158971766L;
    071
    072            @Override
    073            protected boolean removeEldestEntry(final Map.Entry<String, ConstantUtf8> eldest) {
    074                return size() > MAX_ENTRIES;
    075            }
    076        };
    077
    078        // Set the size to 0 or below to skip caching entirely
    079        private static final int MAX_ENTRY_SIZE = Integer.getInteger(SYS_PROP_CACHE_MAX_ENTRY_SIZE, 200).intValue();
    080
    081        static boolean isEnabled() {
    082            return MAX_ENTRIES > 0 && MAX_ENTRY_SIZE > 0;
    083        }
    084
    085    }
    086
    087    // TODO these should perhaps be AtomicInt?
    088    private static volatile int considered;
    089    private static volatile int created;
    090    private static volatile int hits;
    091    private static volatile int skipped;
    092
    093    private static final String SYS_PROP_CACHE_MAX_ENTRIES = "bcel.maxcached";
    094    private static final String SYS_PROP_CACHE_MAX_ENTRY_SIZE = "bcel.maxcached.size";
    095    private static final String SYS_PROP_STATISTICS = "bcel.statistics";
    096
    097    static {
    098        if (Cache.BCEL_STATISTICS) {
    099            Runtime.getRuntime().addShutdownHook(new Thread(ConstantUtf8::printStats));
    100        }
    101    }
    102
    103    /**
    104     * Clears the cache.
    105     *
    106     * @since 6.4.0
    107     */
    108    public static synchronized void clearCache() {
    109        Cache.CACHE.clear();
    110    }
    111
    112    // for access by test code
    113    static synchronized void clearStats() {
    114        hits = considered = skipped = created = 0;
    115    }
    116
    117    // Avoid Spotbugs complaint about Write to static field
    118    private static synchronized void countCreated() {
    119        created++;
    120    }
    121
    122    /**
    123     * Gets a new or cached instance of the given value.
    124     * <p>
    125     * See {@link ConstantUtf8} class Javadoc for details.
    126     * </p>
    127     *
    128     * @param value the value.
    129     * @return a new or cached instance of the given value.
    130     * @since 6.0
    131     */
    132    public static synchronized ConstantUtf8 getCachedInstance(final String value) {
    133        if (value.length() > Cache.MAX_ENTRY_SIZE) {
    134            skipped++;
    135            return new ConstantUtf8(value);
    136        }
    137        considered++;
    138        synchronized (ConstantUtf8.class) { // might be better with a specific lock object
    139            ConstantUtf8 result = Cache.CACHE.get(value);
    140            if (result != null) {
    141                hits++;
    142                return result;
    143            }
    144            result = new ConstantUtf8(value);
    145            Cache.CACHE.put(value, result);
    146            return result;
    147        }
    148    }
    149
    150    /**
    151     * Gets a new or cached instance of the given value.
    152     * <p>
    153     * See {@link ConstantUtf8} class Javadoc for details.
    154     * </p>
    155     *
    156     * @param dataInput the value.
    157     * @return a new or cached instance of the given value.
    158     * @throws IOException if an I/O error occurs.
    159     * @since 6.0
    160     */
    161    public static ConstantUtf8 getInstance(final DataInput dataInput) throws IOException {
    162        return getInstance(dataInput.readUTF());
    163    }
    164
    165    /**
    166     * Gets a new or cached instance of the given value.
    167     * <p>
    168     * See {@link ConstantUtf8} class Javadoc for details.
    169     * </p>
    170     *
    171     * @param value the value.
    172     * @return a new or cached instance of the given value.
    173     * @since 6.0
    174     */
    175    public static ConstantUtf8 getInstance(final String value) {
    176        return Cache.isEnabled() ? getCachedInstance(value) : new ConstantUtf8(value);
    177    }
    178
    179    // for access by test code
    180    static void printStats() {
    181        final String prefix = "[Apache Commons BCEL]";
    182        System.err.printf("%s Cache hit %,d/%,d, %d skipped.%n", prefix, hits, considered, skipped);
    183        System.err.printf("%s Total of %,d ConstantUtf8 objects created.%n", prefix, created);
    184        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,
    185            Cache.MAX_ENTRY_SIZE);
    186    }
    187
    188    private final String value;
    189
    190    /**
    191     * Initializes from another object.
    192     *
    193     * @param constantUtf8 the value.
    194     */
    195    public ConstantUtf8(final ConstantUtf8 constantUtf8) {
    196        this(constantUtf8.getBytes());
    197    }
    198
    199    /**
    200     * Initializes instance from file data.
    201     *
    202     * @param dataInput Input stream
    203     * @throws IOException if an I/O error occurs.
    204     */
    205    ConstantUtf8(final DataInput dataInput) throws IOException {
    206        super(Const.CONSTANT_Utf8);
    207        value = dataInput.readUTF();
    208        countCreated();
    209    }
    210
    211    /**
    212     * @param value Data
    213     */
    214    public ConstantUtf8(final String value) {
    215        super(Const.CONSTANT_Utf8);
    216        this.value = Objects.requireNonNull(value, "value");
    217        countCreated();
    218    }
    219
    220    /**
    221     * Called by objects that are traversing the nodes of the tree implicitly defined by the contents of a Java class.
    222     * I.e., the hierarchy of methods, fields, attributes, etc. spawns a tree of objects.
    223     *
    224     * @param v Visitor object
    225     */
    226    @Override
    227    public void accept(final Visitor v) {
    228        v.visitConstantUtf8(this);
    229    }
    230
    231    /**
    232     * Dumps String in Utf8 format to file stream.
    233     *
    234     * @param file Output file stream
    235     * @throws IOException if an I/O error occurs.
    236     */
    237    @Override
    238    public void dump(final DataOutputStream file) throws IOException {
    239        file.writeByte(super.getTag());
    240        file.writeUTF(value);
    241    }
    242
    243    /**
    244     * @return Data converted to string.
    245     */
    246    public String getBytes() {
    247        return value;
    248    }
    249
    250    /**
    251     * @param bytes the raw bytes of this UTF-8
    252     * @deprecated (since 6.0)
    253     */
    254    @java.lang.Deprecated
    255    public void setBytes(final String bytes) {
    256        throw new UnsupportedOperationException();
    257    }
    258
    259    /**
    260     * @return String representation
    261     */
    262    @Override
    263    public String toString() {
    264        return super.toString() + "(\"" + Utility.replace(value, "\n", "\\n") + "\")";
    265    }
    266}