Introduce Predicate-based QueryEngine.

Closes: #565

Author: christophstrobl

src/main/java/org/springframework/data/keyvalue/core/PredicateQueryEngine.java

@@ -0,0 +1,97 @@
+/*
+ * Copyright 2024 the original author or authors.
+ *
+ * Licensed 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
+ *
+ *      https://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.springframework.data.keyvalue.core;
+
+import java.util.Collection;
+import java.util.Comparator;
+import java.util.List;
+import java.util.function.Predicate;
+import java.util.stream.Collectors;
+import java.util.stream.Stream;
+
+import org.springframework.data.keyvalue.core.query.KeyValueQuery;
+import org.springframework.lang.Nullable;
+
+/**
+ * {@link QueryEngine} implementation specific for executing {@link Predicate} based {@link KeyValueQuery} against
+ * {@link KeyValueAdapter}.
+ *
+ * @author Christoph Strobl
+ * @since 3.3
+ */
+class PredicateQueryEngine extends QueryEngine<KeyValueAdapter, Predicate<?>, Comparator<?>> {
+
+	/**
+	 * Creates a new {@link PredicateQueryEngine}.
+	 */
+	public PredicateQueryEngine() {
+		this(new PathSortAccessor());
+	}
+
+	/**
+	 * Creates a new query engine using provided {@link SortAccessor accessor} for sorting results.
+	 */
+	public PredicateQueryEngine(SortAccessor<Comparator<?>> sortAccessor) {
+		super(new CriteriaAccessor<>() {
+			@Nullable
+			@Override
+			public Predicate<?> resolve(KeyValueQuery<?> query) {
+				return (Predicate<?>) query.getCriteria();
+			}
+		}, sortAccessor);
+	}
+
+	@Override
+	public Collection<?> execute(@Nullable Predicate<?> criteria, @Nullable Comparator<?> sort, long offset, int rows,
+			String keyspace) {
+		return sortAndFilterMatchingRange(getRequiredAdapter().getAllOf(keyspace), criteria, sort, offset, rows);
+	}
+
+	@Override
+	public long count(@Nullable Predicate<?> criteria, String keyspace) {
+		return filterMatchingRange(IterableConverter.toList(getRequiredAdapter().getAllOf(keyspace)), criteria, -1, -1)
+				.size();
+	}
+
+	@SuppressWarnings({ "unchecked", "rawtypes" })
+	private List<?> sortAndFilterMatchingRange(Iterable<?> source, @Nullable Predicate<?> criteria,
+			@Nullable Comparator sort, long offset, int rows) {
+
+		List<?> tmp = IterableConverter.toList(source);
+		if (sort != null) {
+			tmp.sort(sort);
+		}
+
+		return filterMatchingRange(tmp, criteria, offset, rows);
+	}
+
+	private static <S> List<S> filterMatchingRange(List<S> source, @Nullable Predicate criteria, long offset, int rows) {
+
+		Stream<S> stream = source.stream();
+
+		if (criteria != null) {
+			stream = stream.filter(criteria);
+		}
+		if (offset > 0) {
+			stream = stream.skip(offset);
+		}
+		if (rows > 0) {
+			stream = stream.limit(rows);
+		}
+
+		return stream.collect(Collectors.toList());
+	}
+}

src/main/java/org/springframework/data/keyvalue/core/SimplePropertyPathAccessor.java

@@ -23,15 +23,15 @@
  * @author Christoph Strobl
  * @since 3.1.10
  */
-class SimplePropertyPathAccessor<T> {
+public class SimplePropertyPathAccessor<T> {
 
 	private final Object root;
 
 	public SimplePropertyPathAccessor(Object source) {
 		this.root = source;
 	}
 
-	Object getValue(PropertyPath path) {
+	public Object getValue(PropertyPath path) {
 
 		Object currentValue = root;
 		for (PropertyPath current : path) {