Bael 2712 lombok builder singular (#6435)

* updated lombok libs to 1.18.4

* sketched out basic test class for @singular

* more examples showing other collection types, non-standard plural

* fixed indentation

lombok/src/main/java/com/baeldung/lombok/builder/singular/Person.java

@@ -0,0 +1,25 @@
+package com.baeldung.lombok.builder.singular;
+
+import lombok.Builder;
+import lombok.Getter;
+import lombok.Singular;
+
+import java.time.LocalDate;
+import java.util.Date;
+import java.util.List;
+import java.util.Map;
+import java.util.Set;
+
+@Getter
+@Builder
+public class Person {
+
+    private final String givenName;
+    private final String additionalName;
+    private final String familyName;
+
+    private final List<String> tags;
+    @Singular private final List<String> interests;
+    @Singular private final Set<String> skills;
+    @Singular private final Map<String, LocalDate> awards;
+}

lombok/src/main/java/com/baeldung/lombok/builder/singular/Sea.java

@@ -0,0 +1,14 @@
+package com.baeldung.lombok.builder.singular;
+
+import java.util.List;
+import lombok.Builder;
+import lombok.Getter;
+import lombok.Singular;
+
+@Getter
+@Builder
+public class Sea {
+
+    @Singular private final List<String> grasses;
+    @Singular("oneFish") private final List<String> fish;
+}

lombok/src/test/java/com/baeldung/lombok/builder/singular/BuilderWithSingularSupportForCollectionsUnitTest.java

@@ -0,0 +1,192 @@
+package com.baeldung.lombok.builder.singular;
+
+import org.junit.Test;
+
+import java.time.LocalDate;
+import java.util.ArrayList;
+import java.util.Arrays;
+import java.util.List;
+
+import static org.hamcrest.MatcherAssert.assertThat;
+import static org.hamcrest.Matchers.*;
+
+public class BuilderWithSingularSupportForCollectionsUnitTest {
+
+    @Test
+    public void canAddMultipleElementsAsNewCollection() throws Exception {
+        Person person = Person.builder()
+            .givenName("Aaron")
+            .additionalName("A")
+            .familyName("Aardvark")
+            .tags(Arrays.asList("fictional", "incidental"))
+            .build();
+
+        assertThat(person.getTags(), containsInAnyOrder("fictional", "incidental"));
+    }
+
+    @Test
+    public void canUpdateCollectionAfterBuildIfMutableCollectionPassedToBuilder() throws Exception {
+
+        List<String> tags = new ArrayList();
+        tags.add("fictional");
+        tags.add("incidental");
+        Person person = Person.builder()
+            .givenName("Aaron")
+            .additionalName("A")
+            .familyName("Aardvark")
+            .tags(tags)
+            .build();
+        person.getTags()
+            .clear();
+        person.getTags()
+            .add("non-fictional");
+        person.getTags()
+            .add("important");
+
+        assertThat(person.getTags(), containsInAnyOrder("non-fictional", "important"));
+    }
+
+    @Test(expected = UnsupportedOperationException.class)
+    public void cannotUpdateCollectionAfterBuildIfImmutableCollectionPassedToBuilder() throws Exception {
+        List<String> tags = Arrays.asList("fictional", "incidental");
+        Person person = Person.builder()
+            .givenName("Aaron")
+            .additionalName("A")
+            .familyName("Aardvark")
+            .tags(tags)
+            .build();
+        person.getTags()
+            .clear();
+    }
+
+    @Test
+    public void canAssignToSingularAnnotatedCollectionOneByOne() throws Exception {
+
+        Person person = Person.builder()
+            .givenName("Aaron")
+            .additionalName("A")
+            .familyName("Aardvark")
+            .interest("history")
+            .interest("sport")
+            .build();
+
+        assertThat(person.getInterests(), containsInAnyOrder("sport", "history"));
+    }
+
+    @Test(expected = UnsupportedOperationException.class)
+    public void singularAnnotatedBuilderCreatesImmutableCollection() throws Exception {
+
+        Person person = Person.builder()
+            .givenName("Aaron")
+            .additionalName("A")
+            .familyName("Aardvark")
+            .interest("history")
+            .interest("sport")
+            .build();
+        person.getInterests()
+            .clear();
+    }
+
+    @Test
+    public void unpopulatedListsCreatedAsNullIfNotSingularButEmptyArrayIfSingular() throws Exception {
+
+        Person person = Person.builder()
+            .givenName("Aaron")
+            .additionalName("A")
+            .familyName("Aardvark")
+            .build();
+        assertThat(person.getInterests(), hasSize(0));
+        assertThat(person.getSkills(), hasSize(0));
+        assertThat(person.getAwards()
+            .keySet(), hasSize(0));
+        assertThat(person.getTags(), is(nullValue()));
+    }
+
+    @Test
+    public void singularSupportsSetsToo() throws Exception {
+
+        Person person = Person.builder()
+            .givenName("Aaron")
+            .additionalName("A")
+            .familyName("Aardvark")
+            .skill("singing")
+            .skill("dancing")
+            .build();
+        assertThat(person.getSkills(), contains("singing", "dancing"));
+    }
+
+    @Test
+    public void singularSetsAreLenientWithDuplicates() throws Exception {
+
+        Person person = Person.builder()
+            .givenName("Aaron")
+            .additionalName("A")
+            .familyName("Aardvark")
+            .interest("singing")
+            .interest("singing")
+            .skill("singing")
+            .skill("singing")
+            .build();
+        assertThat(person.getInterests(), contains("singing", "singing"));
+        assertThat(person.getSkills(), contains("singing"));
+    }
+
+    @Test
+    public void singularSupportsMapsToo() throws Exception {
+
+        Person person = Person.builder()
+            .givenName("Aaron")
+            .additionalName("A")
+            .familyName("Aardvark")
+            .award("Singer of the Year", LocalDate.now()
+                .minusYears(5))
+            .award("Best Dancer", LocalDate.now()
+                .minusYears(2))
+            .build();
+        assertThat(person.getAwards()
+            .keySet(), contains("Singer of the Year", "Best Dancer"));
+        assertThat(person.getAwards()
+            .get("Best Dancer"),
+            is(LocalDate.now()
+                .minusYears(2)));
+    }
+
+    @Test
+    public void singularIsLenientWithMapKeys() throws Exception {
+
+        Person person = Person.builder()
+            .givenName("Aaron")
+            .additionalName("A")
+            .familyName("Aardvark")
+            .award("Best Dancer", LocalDate.now()
+                .minusYears(5))
+            .award("Best Dancer", LocalDate.now()
+                .minusYears(4))
+            .award("Best Dancer", LocalDate.now()
+                .minusYears(3))
+            .award("Best Dancer", LocalDate.now()
+                .minusYears(2))
+            .award("Best Dancer", LocalDate.now()
+                .minusYears(1))
+            .build();
+        assertThat(person.getAwards()
+            .keySet(), hasSize(1));
+        assertThat(person.getAwards()
+            .get("Best Dancer"),
+            is(LocalDate.now()
+                .minusYears(1)));
+    }
+
+    @Test
+    public void wordsWithNonStandardPlurals() throws Exception {
+        Sea sea = Sea.builder()
+            .grass("Dulse")
+            .grass("Kelp")
+            .oneFish("Cod")
+            .oneFish("Mackerel")
+            .build();
+        assertThat(sea.getGrasses(), contains("Dulse", "Kelp"));
+        assertThat(sea.getFish(), contains("Cod", "Mackerel"));
+    }
+
+}