Sonar code smell fixes in web package (#4512)

Signed-off-by: Gino Augustine <ginoaugustine@gmail.com>
Co-authored-by: Vladimir Kotal <vlada@kotalovi.cz>

Author: ginoaugustine

opengrok-indexer/src/main/java/org/opengrok/indexer/util/ErrorMessageCollector.java

@@ -0,0 +1,142 @@
+/*
+ * CDDL HEADER START
+ *
+ * The contents of this file are subject to the terms of the
+ * Common Development and Distribution License (the "License").
+ * You may not use this file except in compliance with the License.
+ *
+ * See LICENSE.txt included in this distribution for the specific
+ * language governing permissions and limitations under the License.
+ *
+ * When distributing Covered Code, include this CDDL HEADER in each
+ * file and include the License file at LICENSE.txt.
+ * If applicable, add the following below this CDDL HEADER, with the
+ * fields enclosed by brackets "[]" replaced with your own identifying
+ * information: Portions Copyright [yyyy] [name of copyright owner]
+ *
+ * CDDL HEADER END
+ */
+
+/*
+ * Copyright (c) 2024, Oracle and/or its affiliates.
+ * Portions Copyright (c) 2024, Gino Augustine <gino.augustine@oracle.com>.
+ */
+package org.opengrok.indexer.util;
+
+import org.jetbrains.annotations.NotNull;
+
+import java.util.Collections;
+import java.util.Objects;
+import java.util.Optional;
+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;
+
+/**
+ * Custom collector to collect error messages for list of projects and join them with comma.
+ *
+ *
+ * @author Gino Augustine
+ */
+public class ErrorMessageCollector implements Collector<String, StringJoiner, Optional<String>> {
+
+    private final String prefix;
+    private final String emptyString;
+    private final boolean returnNullWhenEmpty;
+
+    /**
+     * Creates a collector with given prefix and
+     * returns optional empty for empty collection.
+     * @param prefix prefix before the joined string
+     */
+    public ErrorMessageCollector(@NotNull String prefix) {
+        Objects.requireNonNull(prefix);
+        this.prefix = prefix;
+        this.emptyString = "";
+        this.returnNullWhenEmpty = true;
+    }
+
+    /**
+     * Creates a string joiner with given prefix and empty string.
+     * @param prefix prefix before the joined string
+     * @param emptyString string to display if collection is empty
+     */
+    public ErrorMessageCollector(@NotNull String prefix, @NotNull String emptyString) {
+        Objects.requireNonNull(prefix);
+        Objects.requireNonNull(emptyString);
+        this.prefix = prefix;
+        this.emptyString = emptyString;
+        this.returnNullWhenEmpty = false;
+
+    }
+    /**
+     * A function that creates and returns a new mutable result container.
+     *
+     * @return a function which returns a new, mutable result container
+     */
+    @Override
+    public Supplier<StringJoiner> supplier() {
+        return () -> {
+            var joiner = new StringJoiner(", ", prefix, "");
+            joiner.setEmptyValue(emptyString);
+            return joiner;
+        };
+    }
+
+    /**
+     * A function that folds a value into a mutable result container.
+     *
+     * @return a function which folds a value into a mutable result container
+     */
+    @Override
+    public BiConsumer<StringJoiner, String> accumulator() {
+        return StringJoiner::add;
+    }
+
+    /**
+     * A function that accepts two partial results and merges them.  The
+     * combiner function may fold state from one argument into the other and
+     * return that, or may return a new result container.
+     *
+     * @return a function which combines two partial results into a combined
+     * result
+     */
+    @Override
+    public BinaryOperator<StringJoiner> combiner() {
+        return StringJoiner::merge;
+    }
+
+    /**
+     * Perform the final transformation from the intermediate accumulation type
+     * {@code A} to the final result type {@code R}.
+     *
+     * <p>If the characteristic {@code IDENTITY_FINISH} is
+     * set, this function may be presumed to be an identity transform with an
+     * unchecked cast from {@code A} to {@code R}.
+     *
+     * @return a function which transforms the intermediate result to the final
+     * result
+     */
+    @Override
+    public Function<StringJoiner, Optional<String>> finisher() {
+        return stringJoiner ->
+            Optional.of(stringJoiner.toString())
+                    .filter(msg -> !(msg.isEmpty() && returnNullWhenEmpty));
+
+    }
+
+    /**
+     * Returns a {@code Set} of {@code Collector.Characteristics} indicating
+     * the characteristics of this Collector.  This set should be immutable.
+     *
+     * @return an immutable set of collector characteristics
+     */
+    @Override
+    public Set<Characteristics> characteristics() {
+        return Collections.emptySet();
+    }
+}