    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 *      https://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 */
    017
    018package org.apache.commons.lang3;
    019
    020import java.io.IOException;
    021import java.util.Iterator;
    022import java.util.StringJoiner;
    023import java.util.function.Supplier;
    024
    025import org.apache.commons.lang3.exception.UncheckedException;
    026import org.apache.commons.lang3.function.FailableBiConsumer;
    027
    028/**
    029 * Joins an array or {@link Iterable} into an existing {@link Appendable} like a {@link StringBuilder}; with the goal for call sites to avoid creating
    030 * intermediary Strings. This is like {@link String#join(CharSequence, CharSequence...)}, {@link String#join(CharSequence, Iterable)}, and {@link StringJoiner}.
    031 * <p>
    032 * Keep an instance in a (static) variable for efficient joining into an {@link Appendable} or {@link StringBuilder} without creating temporary Strings.
    033 * </p>
    034 * <p>
    035 * Use the builder and instance methods to reuse the same kind of joining prefix, suffix, delimiter, and string conversion.
    036 * </p>
    037 * <p>
    038 * For example:
    039 * </p>
    040 *
    041 * <pre>{@code
    042 * // A reuseable instance
    043 * private static final AppendableJoiner<Object> JOINER = AppendableJoiner.builder()
    044 *     .setPrefix("[")
    045 *     .setSuffix("]")
    046 *     .setDelimiter(", ")
    047 *     .get();
    048 * }
    049 * ...
    050 * // Builds straight into a StringBuilder:
    051 * StringBuilder sbuilder = new StringBuilder("1");
    052 * JOINER.join(sbuilder, "A", "B");
    053 * sbuilder.append("2");
    054 * JOINER.join(sbuilder, "C", "D");
    055 * sbuilder.append("3");
    056 * // Returns "1[A, B]2[C, D]3"
    057 * return sbuilder.toString();
    058 * }</pre>
    059 * <p>
    060 * To provide a custom Object element to {@link CharSequence} converter, call {@link Builder#setElementAppender(FailableBiConsumer)}, for example:
    061 * </p>
    062 *
    063 * <pre>{@code
    064 * private static final AppendableJoiner<Item> JOINER = AppendableJoiner.builder()
    065 *     .setElementAppender(e -> (a, e) -> a.append(e.getFoo())
    066 *                                        a.append(e.getBar())
    067 *                                        a.append('!'))
    068 *     ...
    069 *     .get();
    070 * }
    071 * }</pre>
    072 * <p>
    073 * This class is immutable and thread-safe.
    074 * </p>
    075 *
    076 * @param <T> the type of elements to join.
    077 * @see Appendable
    078 * @see StringBuilder
    079 * @see String#join(CharSequence, CharSequence...)
    080 * @see String#join(CharSequence, Iterable)
    081 * @see StringJoiner
    082 * @since 3.15.0
    083 */
    084public final class AppendableJoiner<T> {
    085
    086    /**
    087     * Builds instances of {@link AppendableJoiner}.
    088     *
    089     * @param <T> the type of elements to join.
    090     */
    091    public static final class Builder<T> implements Supplier<AppendableJoiner<T>> {
    092
    093        /** The sequence of characters to be used at the beginning. */
    094        private CharSequence prefix;
    095
    096        /** The sequence of characters to be used at the end. */
    097        private CharSequence suffix;
    098
    099        /** The delimiter that separates each element. */
    100        private CharSequence delimiter;
    101
    102        /** The consumer used to render each element of type {@code T} onto an {@link Appendable}. */
    103        private FailableBiConsumer<Appendable, T, IOException> appender;
    104
    105        /**
    106         * Constructs a new instance.
    107         */
    108        Builder() {
    109            // empty
    110        }
    111
    112        /**
    113         * Gets a new instance of {@link AppendableJoiner}.
    114         */
    115        @Override
    116        public AppendableJoiner<T> get() {
    117            return new AppendableJoiner<>(prefix, suffix, delimiter, appender);
    118        }
    119
    120        /**
    121         * Sets the delimiter that separates each element.
    122         *
    123         * @param delimiter The delimiter that separates each element.
    124         * @return {@code this} instance.
    125         */
    126        public Builder<T> setDelimiter(final CharSequence delimiter) {
    127            this.delimiter = delimiter;
    128            return this;
    129        }
    130
    131        /**
    132         * Sets the consumer used to render each element of type {@code T} onto an {@link Appendable}.
    133         *
    134         * @param appender The consumer used to render each element of type {@code T} onto an {@link Appendable}.
    135         * @return {@code this} instance.
    136         */
    137        public Builder<T> setElementAppender(final FailableBiConsumer<Appendable, T, IOException> appender) {
    138            this.appender = appender;
    139            return this;
    140        }
    141
    142        /**
    143         * Sets the sequence of characters to be used at the beginning.
    144         *
    145         * @param prefix The sequence of characters to be used at the beginning.
    146         * @return {@code this} instance.
    147         */
    148        public Builder<T> setPrefix(final CharSequence prefix) {
    149            this.prefix = prefix;
    150            return this;
    151        }
    152
    153        /**
    154         * Sets the sequence of characters to be used at the end.
    155         *
    156         * @param suffix The sequence of characters to be used at the end.
    157         * @return {@code this} instance.
    158         */
    159        public Builder<T> setSuffix(final CharSequence suffix) {
    160            this.suffix = suffix;
    161            return this;
    162        }
    163
    164    }
    165
    166    /**
    167     * Creates a new builder.
    168     *
    169     * @param <T> The type of elements.
    170     * @return a new builder.
    171     */
    172    public static <T> Builder<T> builder() {
    173        return new Builder<>();
    174    }
    175
    176    /** Could be public in the future, in some form. */
    177    @SafeVarargs
    178    static <A extends Appendable, T> A joinA(final A appendable, final CharSequence prefix, final CharSequence suffix, final CharSequence delimiter,
    179            final FailableBiConsumer<Appendable, T, IOException> appender, final T... elements) throws IOException {
    180        return joinArray(appendable, prefix, suffix, delimiter, appender, elements);
    181    }
    182
    183    private static <A extends Appendable, T> A joinArray(final A appendable, final CharSequence prefix, final CharSequence suffix, final CharSequence delimiter,
    184            final FailableBiConsumer<Appendable, T, IOException> appender, final T[] elements) throws IOException {
    185        appendable.append(prefix);
    186        if (elements != null) {
    187            if (elements.length > 0) {
    188                appender.accept(appendable, elements[0]);
    189            }
    190            for (int i = 1; i < elements.length; i++) {
    191                appendable.append(delimiter);
    192                appender.accept(appendable, elements[i]);
    193            }
    194        }
    195        appendable.append(suffix);
    196        return appendable;
    197    }
    198
    199    /** Could be public in the future, in some form. */
    200    static <T> StringBuilder joinI(final StringBuilder stringBuilder, final CharSequence prefix, final CharSequence suffix, final CharSequence delimiter,
    201            final FailableBiConsumer<Appendable, T, IOException> appender, final Iterable<T> elements) {
    202        try {
    203            return joinIterable(stringBuilder, prefix, suffix, delimiter, appender, elements);
    204        } catch (final IOException e) {
    205            // Cannot happen with a StringBuilder.
    206            throw new UncheckedException(e);
    207        }
    208    }
    209
    210    private static <A extends Appendable, T> A joinIterable(final A appendable, final CharSequence prefix, final CharSequence suffix,
    211            final CharSequence delimiter, final FailableBiConsumer<Appendable, T, IOException> appender, final Iterable<T> elements) throws IOException {
    212        appendable.append(prefix);
    213        if (elements != null) {
    214            final Iterator<T> iterator = elements.iterator();
    215            if (iterator.hasNext()) {
    216                appender.accept(appendable, iterator.next());
    217            }
    218            while (iterator.hasNext()) {
    219                appendable.append(delimiter);
    220                appender.accept(appendable, iterator.next());
    221            }
    222        }
    223        appendable.append(suffix);
    224        return appendable;
    225    }
    226
    227    /** Could be public in the future, in some form. */
    228    @SafeVarargs
    229    static <T> StringBuilder joinSB(final StringBuilder stringBuilder, final CharSequence prefix, final CharSequence suffix, final CharSequence delimiter,
    230            final FailableBiConsumer<Appendable, T, IOException> appender, final T... elements) {
    231        try {
    232            return joinArray(stringBuilder, prefix, suffix, delimiter, appender, elements);
    233        } catch (final IOException e) {
    234            // Cannot happen with a StringBuilder.
    235            throw new UncheckedException(e);
    236        }
    237    }
    238
    239    private static CharSequence nonNull(final CharSequence value) {
    240        return value != null ? value : StringUtils.EMPTY;
    241    }
    242
    243    /** The sequence of characters to be used at the beginning. */
    244    private final CharSequence prefix;
    245
    246    /** The sequence of characters to be used at the end. */
    247    private final CharSequence suffix;
    248
    249    /** The delimiter that separates each element. */
    250    private final CharSequence delimiter;
    251
    252    private final FailableBiConsumer<Appendable, T, IOException> appender;
    253
    254    /**
    255     * Constructs a new instance.
    256     */
    257    private AppendableJoiner(final CharSequence prefix, final CharSequence suffix, final CharSequence delimiter,
    258            final FailableBiConsumer<Appendable, T, IOException> appender) {
    259        this.prefix = nonNull(prefix);
    260        this.suffix = nonNull(suffix);
    261        this.delimiter = nonNull(delimiter);
    262        this.appender = appender != null ? appender : (a, e) -> a.append(String.valueOf(e));
    263    }
    264
    265    /**
    266     * Joins stringified objects from the given Iterable into a StringBuilder.
    267     *
    268     * @param stringBuilder The target.
    269     * @param elements      The source.
    270     * @return The given StringBuilder.
    271     */
    272    public StringBuilder join(final StringBuilder stringBuilder, final Iterable<T> elements) {
    273        return joinI(stringBuilder, prefix, suffix, delimiter, appender, elements);
    274    }
    275
    276    /**
    277     * Joins stringified objects from the given array into a StringBuilder.
    278     *
    279     * @param stringBuilder The target.
    280     * @param elements      The source.
    281     * @return the given target StringBuilder.
    282     */
    283    public StringBuilder join(final StringBuilder stringBuilder, @SuppressWarnings("unchecked") final T... elements) {
    284        return joinSB(stringBuilder, prefix, suffix, delimiter, appender, elements);
    285    }
    286
    287    /**
    288     * Joins stringified objects from the given Iterable into an Appendable.
    289     *
    290     * @param <A>        the Appendable type.
    291     * @param appendable The target.
    292     * @param elements   The source.
    293     * @return The given StringBuilder.
    294     * @throws IOException If an I/O error occurs
    295     */
    296    public <A extends Appendable> A joinA(final A appendable, final Iterable<T> elements) throws IOException {
    297        return joinIterable(appendable, prefix, suffix, delimiter, appender, elements);
    298    }
    299
    300    /**
    301     * Joins stringified objects from the given array into an Appendable.
    302     *
    303     * @param <A>        the Appendable type.
    304     * @param appendable The target.
    305     * @param elements   The source.
    306     * @return The given StringBuilder.
    307     * @throws IOException If an I/O error occurs
    308     */
    309    public <A extends Appendable> A joinA(final A appendable, @SuppressWarnings("unchecked") final T... elements) throws IOException {
    310        return joinA(appendable, prefix, suffix, delimiter, appender, elements);
    311    }
    312
    313}