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Merged
SirCotare merged 2 commits into from
Sep 30, 2025
Merged

add filter util #36

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d441b3c
add filter util
SirCotare Sep 30, 2025
b7d0c5e
add tests
SirCotare Sep 30, 2025
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72 changes: 72 additions & 0 deletions src/main/java/it/aboutbits/springboot/toolbox/util/FilterUtil.java
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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.Set;
import java.util.function.Predicate;
import java.util.stream.Collectors;
import java.util.stream.Stream;

/**
* This is a collection of tools to simply filter items to a new collection or stream.
* <p>
* The returned collections are unmodifiable.
*/
public final class FilterUtil {
private FilterUtil() {
}

public static <T> Set<T> filterToSet(@NonNull Collection<T> items, @NonNull Predicate<T> filter) {
return items.stream()
.filter(filter)
.collect(Collectors.toUnmodifiableSet());
}

public static <T> Set<T> filterToSet(@NonNull Streamable<T> items, @NonNull Predicate<T> filter) {
return items.stream()
.filter(filter)
.collect(Collectors.toUnmodifiableSet());
}

public static <T> Set<T> filterToSet(@NonNull Stream<T> items, @NonNull Predicate<T> filter) {
return items
.filter(filter)
.collect(Collectors.toUnmodifiableSet());
}

public static <T> List<T> filterToList(@NonNull Collection<T> items, @NonNull Predicate<T> filter) {
return items.stream()
.filter(filter)
.toList();
}

public static <T> List<T> filterToList(@NonNull Streamable<T> items, @NonNull Predicate<T> filter) {
return items.stream()
.filter(filter)
.toList();
}

public static <T> List<T> filterToList(@NonNull Stream<T> items, @NonNull Predicate<T> filter) {
return items
.filter(filter)
.toList();
}

public static <T> Stream<T> filterToStream(@NonNull Collection<T> items, @NonNull Predicate<T> filter) {
return items.stream()
.filter(filter);
}

public static <T> Stream<T> filterToStream(@NonNull Streamable<T> items, @NonNull Predicate<T> filter) {
return items.stream()
.filter(filter);
}

public static <T> Stream<T> filterToStream(@NonNull Stream<T> items, @NonNull Predicate<T> filter) {
return items
.filter(filter);
}
}
265 changes: 265 additions & 0 deletions src/test/java/it/aboutbits/springboot/toolbox/util/FilterUtilTest.java
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package it.aboutbits.springboot.toolbox.util;

import org.junit.jupiter.api.DisplayName;
import org.junit.jupiter.api.Nested;
import org.junit.jupiter.api.Test;
import org.springframework.data.util.Streamable;

import java.util.Arrays;
import java.util.Collections;
import java.util.stream.Stream;

import static org.assertj.core.api.Assertions.assertThat;
import static org.junit.jupiter.api.Assertions.assertTrue;

class FilterUtilTest {
@Nested
class FilterToSet {
@Test
@DisplayName("Should filter Collection to Set using predicate")
void shouldFilterCollectionToSetUsingPredicate() {
// given
var numbers = Arrays.asList(1, 2, 3, 4, 5);

// when
var result = FilterUtil.filterToSet(numbers, n -> n > 2);

// then
assertThat(result).containsExactlyInAnyOrder(3, 4, 5);
}

@Test
@DisplayName("Should handle empty Collection when filtering to Set")
void shouldHandleEmptyCollectionWhenFilteringToSet() {
// given
var emptyList = Collections.<Integer>emptyList();

// when
var result = FilterUtil.filterToSet(emptyList, n -> n > 2);

// then
assertTrue(result.isEmpty());
}

@Test
@DisplayName("Should remove duplicates when filtering Collection to Set")
void shouldRemoveDuplicatesWhenFilteringCollectionToSet() {
// given
var numbersWithDuplicates = Arrays.asList(1, 2, 2, 3, 3, 3);

// when
var result = FilterUtil.filterToSet(numbersWithDuplicates, n -> n >= 2);

// then
assertThat(result).containsExactlyInAnyOrder(2, 3);
assertThat(result).hasSize(2);
}

@Test
@DisplayName("Should filter Streamable to Set using predicate")
void shouldFilterStreamableToSetUsingPredicate() {
// given
var numbers = Streamable.of(1, 2, 3, 4, 5);

// when
var result = FilterUtil.filterToSet(numbers, n -> n % 2 == 0);

// then
assertThat(result).containsExactlyInAnyOrder(2, 4);
}

@Test
@DisplayName("Should handle empty Streamable when filtering to Set")
void shouldHandleEmptyStreamableWhenFilteringToSet() {
// given
var emptyStreamable = Streamable.<Integer>empty();

// when
var result = FilterUtil.filterToSet(emptyStreamable, n -> n > 2);

// then
assertTrue(result.isEmpty());
}

@Test
@DisplayName("Should remove duplicates when filtering Stream to Set")
void shouldRemoveDuplicatesWhenFilteringStreamToSet() {
// given
var numbersWithDuplicates = Stream.of(1, 2, 2, 3, 3, 3);

// when
var result = FilterUtil.filterToSet(numbersWithDuplicates, n -> n >= 2);

// then
assertThat(result).containsExactlyInAnyOrder(2, 3);
assertThat(result).hasSize(2);
}
}

@Nested
class FilterToList {
@Test
@DisplayName("Should filter Collection to List using predicate")
void shouldFilterCollectionToListUsingPredicate() {
// given
var numbers = Arrays.asList(1, 2, 3, 4, 5);

// when
var result = FilterUtil.filterToList(numbers, n -> n % 2 == 1);

// then
assertThat(result).containsExactly(1, 3, 5);
}

@Test
@DisplayName("Should handle empty Collection when filtering to List")
void shouldHandleEmptyCollectionWhenFilteringToList() {
// given
var emptyList = Collections.<Integer>emptyList();

// when
var result = FilterUtil.filterToList(emptyList, n -> n > 2);

// then
assertTrue(result.isEmpty());
}

@Test
@DisplayName("Should preserve duplicates when filtering Collection to List")
void shouldPreserveDuplicatesWhenFilteringCollectionToList() {
// given
var numbersWithDuplicates = Arrays.asList(1, 2, 2, 3, 3, 3);

// when
var result = FilterUtil.filterToList(numbersWithDuplicates, n -> n >= 2);

// then
assertThat(result).containsExactly(2, 2, 3, 3, 3);
assertThat(result).hasSize(5);
}

@Test
@DisplayName("Should filter Streamable to List using predicate")
void shouldFilterStreamableToListUsingPredicate() {
// given
var numbers = Streamable.of(1, 2, 3, 4, 5);

// when
var result = FilterUtil.filterToList(numbers, n -> n < 4);

// then
assertThat(result).containsExactly(1, 2, 3);
}

@Test
@DisplayName("Should handle empty Streamable when filtering to List")
void shouldHandleEmptyStreamableWhenFilteringToList() {
// given
var emptyStreamable = Streamable.<Integer>empty();

// when
var result = FilterUtil.filterToList(emptyStreamable, n -> n > 2);

// then
assertTrue(result.isEmpty());
}

@Test
@DisplayName("Should preserve duplicates when filtering Stream to List")
void shouldPreserveDuplicatesWhenFilteringStreamToList() {
// given
var numbersWithDuplicates = Stream.of(1, 2, 2, 3, 3, 3);

// when
var result = FilterUtil.filterToList(numbersWithDuplicates, n -> n >= 2);

// then
assertThat(result).containsExactly(2, 2, 3, 3, 3);
assertThat(result).hasSize(5);
}
}

@Nested
class FilterToStream {
@Test
@DisplayName("Should filter Collection to Stream using predicate")
void shouldFilterCollectionToStreamUsingPredicate() {
// given
var numbers = Arrays.asList(1, 2, 3, 4, 5);

// when
var resultStream = FilterUtil.filterToStream(numbers, n -> n >= 4);

// then
var result = resultStream.toList();
assertThat(result).containsExactly(4, 5);
}

@Test
@DisplayName("Should handle empty Collection when filtering to Stream")
void shouldHandleEmptyCollectionWhenFilteringToStream() {
// given
var emptyList = Collections.<Integer>emptyList();

// when
var resultStream = FilterUtil.filterToStream(emptyList, n -> n > 2);

// then
assertTrue(resultStream.toList().isEmpty());
}

@Test
@DisplayName("Should filter Streamable to Stream using predicate")
void shouldFilterStreamableToStreamUsingPredicate() {
// given
var numbers = Streamable.of(1, 2, 3, 4, 5);

// when
var resultStream = FilterUtil.filterToStream(numbers, n -> n <= 2);

// then
var result = resultStream.toList();
assertThat(result).containsExactly(1, 2);
}

@Test
@DisplayName("Should handle empty Streamable when filtering to Stream")
void shouldHandleEmptyStreamableWhenFilteringToStream() {
// given
var emptyStreamable = Streamable.<Integer>empty();

// when
var resultStream = FilterUtil.filterToStream(emptyStreamable, n -> n > 2);

// then
assertTrue(resultStream.toList().isEmpty());
}

@Test
@DisplayName("Should filter Stream to Stream using predicate")
void shouldFilterStreamToStreamUsingPredicate() {
// given
var numbers = Stream.of(1, 2, 3, 4, 5);

// when
var resultStream = FilterUtil.filterToStream(numbers, n -> n % 2 == 0);

// then
var result = resultStream.toList();
assertThat(result).containsExactly(2, 4);
}

@Test
@DisplayName("Should handle empty Stream when filtering to Stream")
void shouldHandleEmptyStreamWhenFilteringToStream() {
// given
var emptyStream = Stream.<Integer>empty();

// when
var resultStream = FilterUtil.filterToStream(emptyStream, n -> n > 2);

// then
assertTrue(resultStream.toList().isEmpty());
}
}
}