1 files changed, 167 insertions, 0 deletions
diff --git a/src/main/java/org/apache/commons/lang3/stream/LangCollectors.java b/src/main/java/org/apache/commons/lang3/stream/LangCollectors.java
new file mode 100644
index 000000000..abd3b10f8
--- /dev/null
+++ b/src/main/java/org/apache/commons/lang3/stream/LangCollectors.java
@@ -0,0 +1,167 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License.  You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.apache.commons.lang3.stream;
+
+import java.util.Collections;
+import java.util.Objects;
+import java.util.Set;
+import java.util.StringJoiner;
+import java.util.function.BiConsumer;
+import java.util.function.BinaryOperator;
+import java.util.function.Function;
+import java.util.function.Supplier;
+import java.util.stream.Collector;
+import java.util.stream.Collectors;
+
+import org.apache.commons.lang3.StringUtils;
+
+/**
+ * Implementations of {@link Collector} that implement various useful reduction operations.
+ * <p>
+ * This class is called {@code LangCollectors} instead of {@code Collectors} to avoid clashes with {@link Collectors}.
+ * </p>
+ *
+ * @since 3.13.0
+ */
+public final class LangCollectors {
+
+    /**
+     * Simple implementation class for {@code Collector}.
+     *
+     * @param <T> the type of elements to be collected
+     * @param <R> the type of the result
+     */
+    private static class SimpleCollector<T, A, R> implements Collector<T, A, R> {
+
+        private final BiConsumer<A, T> accumulator;
+        private final Set<Characteristics> characteristics;
+        private final BinaryOperator<A> combiner;
+        private final Function<A, R> finisher;
+        private final Supplier<A> supplier;
+
+        private SimpleCollector(final Supplier<A> supplier, final BiConsumer<A, T> accumulator, final BinaryOperator<A> combiner, final Function<A, R> finisher,
+            final Set<Characteristics> characteristics) {
+            this.supplier = supplier;
+            this.accumulator = accumulator;
+            this.combiner = combiner;
+            this.finisher = finisher;
+            this.characteristics = characteristics;
+        }
+
+        @Override
+        public BiConsumer<A, T> accumulator() {
+            return accumulator;
+        }
+
+        @Override
+        public Set<Characteristics> characteristics() {
+            return characteristics;
+        }
+
+        @Override
+        public BinaryOperator<A> combiner() {
+            return combiner;
+        }
+
+        @Override
+        public Function<A, R> finisher() {
+            return finisher;
+        }
+
+        @Override
+        public Supplier<A> supplier() {
+            return supplier;
+        }
+    }
+
+    private static final Set<Collector.Characteristics> CH_NOID = Collections.emptySet();
+
+    /**
+     * Returns a {@code Collector} that concatenates the input elements, separated by the specified delimiter, in encounter
+     * order.
+     * <p>
+     * This is a variation of {@link Collectors#joining()} that works with any element class, not just {@code CharSequence}.
+     * </p>
+     *
+     * @return A {@code Collector} which concatenates Object elements, separated by the specified delimiter, in encounter
+     *         order.
+     */
+    public static Collector<Object, ?, String> joining() {
+        return new SimpleCollector<>(StringBuilder::new, StringBuilder::append, StringBuilder::append, StringBuilder::toString, CH_NOID);
+    }
+
+    /**
+     * Returns a {@code Collector} that concatenates the input elements, separated by the specified delimiter, in encounter
+     * order.
+     * <p>
+     * This is a variation of {@link Collectors#joining(CharSequence)} that works with any element class, not just
+     * {@code CharSequence}.
+     * </p>
+     *
+     * @param delimiter the delimiter to be used between each element.
+     * @return A {@code Collector} which concatenates Object elements, separated by the specified delimiter, in encounter
+     *         order.
+     */
+    public static Collector<Object, ?, String> joining(final CharSequence delimiter) {
+        return joining(delimiter, StringUtils.EMPTY, StringUtils.EMPTY);
+    }
+
+    /**
+     * Returns a {@code Collector} that concatenates the input elements, separated by the specified delimiter, with the
+     * specified prefix and suffix, in encounter order.
+     * <p>
+     * This is a variation of {@link Collectors#joining(CharSequence, CharSequence, CharSequence)} that works with any
+     * element class, not just {@code CharSequence}.
+     * </p>
+     *
+     * @param delimiter the delimiter to be used between each element
+     * @param prefix the sequence of characters to be used at the beginning of the joined result
+     * @param suffix the sequence of characters to be used at the end of the joined result
+     * @return A {@code Collector} which concatenates CharSequence elements, separated by the specified delimiter, in
+     *         encounter order
+     */
+    public static Collector<Object, ?, String> joining(final CharSequence delimiter, final CharSequence prefix, final CharSequence suffix) {
+        return joining(delimiter, prefix, suffix, Objects::toString);
+    }
+
+    /**
+     * Returns a {@code Collector} that concatenates the input elements, separated by the specified delimiter, with the
+     * specified prefix and suffix, in encounter order.
+     * <p>
+     * This is a variation of {@link Collectors#joining(CharSequence, CharSequence, CharSequence)} that works with any
+     * element class, not just {@code CharSequence}.
+     * </p>
+     *
+     * @param delimiter the delimiter to be used between each element
+     * @param prefix the sequence of characters to be used at the beginning of the joined result
+     * @param suffix the sequence of characters to be used at the end of the joined result
+     * @param toString A function that takes an Object and returns a non-null String.
+     * @return A {@code Collector} which concatenates CharSequence elements, separated by the specified delimiter, in
+     *         encounter order
+     */
+    public static Collector<Object, ?, String> joining(final CharSequence delimiter, final CharSequence prefix, final CharSequence suffix,
+        final Function<Object, String> toString) {
+        return new SimpleCollector<>(() -> new StringJoiner(delimiter, prefix, suffix), (a, t) -> a.add(toString.apply(t)), StringJoiner::merge,
+            StringJoiner::toString, CH_NOID);
+    }
+
+    private LangCollectors() {
+        // No instance
+    }
+
+}