add collect utility

src/main/java/it/aboutbits/springboot/toolbox/util/CollectUtil.java

@@ -0,0 +1,114 @@
+package it.aboutbits.springboot.toolbox.util;
+
+import lombok.NonNull;
+import org.springframework.data.util.Streamable;
+
+import java.util.Collection;
+import java.util.List;
+import java.util.Map;
+import java.util.Objects;
+import java.util.Set;
+import java.util.function.Function;
+import java.util.stream.Collectors;
+import java.util.stream.Stream;
+
+/**
+ * This is a collection of tools to simply collect a property to a new collection or stream.
+ * The common usage would, for example, be to collect the ids of all items in a list to a set.
+ * <p>
+ * The returned collections are unmodifiable.
+ */
+public final class CollectUtil {
+    private CollectUtil() {
+    }
+
+    public static <T, R> Set<R> collectToSet(@NonNull Collection<T> items, @NonNull Function<T, R> mapper) {
+        return items.stream()
+                .map(mapper)
+                .filter(Objects::nonNull)
+                .collect(Collectors.toUnmodifiableSet());
+    }
+
+    public static <T, R> Set<R> collectToSet(@NonNull Streamable<T> items, @NonNull Function<T, R> mapper) {
+        return items.stream()
+                .map(mapper)
+                .filter(Objects::nonNull)
+                .collect(Collectors.toUnmodifiableSet());
+    }
+
+    public static <T, R> Set<R> collectToSet(@NonNull Stream<T> items, @NonNull Function<T, R> mapper) {
+        return items
+                .map(mapper)
+                .filter(Objects::nonNull)
+                .collect(Collectors.toUnmodifiableSet());
+    }
+
+    public static <T, R> List<R> collectToList(@NonNull Collection<T> items, @NonNull Function<T, R> mapper) {
+        return items.stream()
+                .map(mapper)
+                .filter(Objects::nonNull)
+                .toList();
+    }
+
+    public static <T, R> List<R> collectToList(@NonNull Streamable<T> items, @NonNull Function<T, R> mapper) {
+        return items.stream()
+                .map(mapper)
+                .filter(Objects::nonNull)
+                .toList();
+    }
+
+    public static <T, R> List<R> collectToList(@NonNull Stream<T> items, @NonNull Function<T, R> mapper) {
+        return items
+                .map(mapper)
+                .filter(Objects::nonNull)
+                .toList();
+    }
+
+    public static <T, R> Stream<R> collectToStream(@NonNull Collection<T> items, @NonNull Function<T, R> mapper) {
+        return items.stream()
+                .map(mapper)
+                .filter(Objects::nonNull);
+    }
+
+    public static <T, R> Stream<R> collectToStream(@NonNull Streamable<T> items, @NonNull Function<T, R> mapper) {
+        return items.stream()
+                .map(mapper)
+                .filter(Objects::nonNull);
+    }
+
+    public static <T, R> Stream<R> collectToStream(@NonNull Stream<T> items, @NonNull Function<T, R> mapper) {
+        return items
+                .map(mapper)
+                .filter(Objects::nonNull);
+    }
+
+    public static <T, K, R> Map<K, R> collectToMap(
+            @NonNull Collection<T> items,
+            @NonNull Function<T, K> keyMapper,
+            @NonNull Function<T, R> valueMapper
+    ) {
+        return items.stream()
+                .filter(Objects::nonNull)
+                .collect(Collectors.toMap(keyMapper, valueMapper));
+    }
+
+    public static <T, K, R> Map<K, R> collectToMap(
+            @NonNull Streamable<T> items,
+            @NonNull Function<T, K> keyMapper,
+            @NonNull Function<T, R> valueMapper
+    ) {
+        return items.stream()
+                .filter(Objects::nonNull)
+                .collect(Collectors.toMap(keyMapper, valueMapper));
+    }
+
+    public static <T, K, R> Map<K, R> collectToMap(
+            @NonNull Stream<T> items,
+            @NonNull Function<T, K> keyMapper,
+            @NonNull Function<T, R> valueMapper
+    ) {
+        return items
+                .filter(Objects::nonNull)
+                .collect(Collectors.toMap(keyMapper, valueMapper));
+    }
+}