DATACMNS-1762 - Extract NullableWrapperConverters from QueryExecutionConverters.

Nullable wrappers such as Java 8 Optional, Guava Optional, Scala Option and Vavr Option are now handled in NullableWrapperConverters and are no longer coupled to QueryExecutionConverters so that this functionality can be reused.

Original Pull Request: #459

src/test/java/org/springframework/data/util/NullableWrapperConvertersUnitTests.java

@@ -0,0 +1,127 @@
+/*
+ * Copyright 2014-2020 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.util;
+
+import static org.assertj.core.api.Assertions.*;
+
+import scala.Option;
+
+import java.util.concurrent.Future;
+
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.Test;
+
+import org.springframework.core.convert.support.DefaultConversionService;
+import org.springframework.util.concurrent.ListenableFuture;
+
+import com.google.common.base.Optional;
+
+/**
+ * Unit tests for {@link NullableWrapperConverters}.
+ *
+ * @author Oliver Gierke
+ * @author Mark Paluch
+ * @author Maciek Opała
+ */
+class NullableWrapperConvertersUnitTests {
+
+	DefaultConversionService conversionService;
+
+	@BeforeEach
+	void setUp() {
+
+		this.conversionService = new DefaultConversionService();
+		NullableWrapperConverters.registerConvertersIn(conversionService);
+	}
+
+	@Test // DATACMNS-714, DATACMNS-1762
+	void registersWrapperTypes() {
+
+		assertThat(NullableWrapperConverters.supports(Optional.class)).isTrue();
+		assertThat(NullableWrapperConverters.supports(java.util.Optional.class)).isTrue();
+		assertThat(NullableWrapperConverters.supports(Future.class)).isFalse();
+		assertThat(NullableWrapperConverters.supports(ListenableFuture.class)).isFalse();
+		assertThat(NullableWrapperConverters.supports(Option.class)).isTrue();
+		assertThat(NullableWrapperConverters.supports(io.vavr.control.Option.class)).isTrue();
+	}
+
+	@Test // DATACMNS-836, DATACMNS-1762
+	void registersUnwrapperTypes() {
+
+		assertThat(NullableWrapperConverters.supportsUnwrapping(Optional.class)).isTrue();
+		assertThat(NullableWrapperConverters.supportsUnwrapping(java.util.Optional.class)).isTrue();
+		assertThat(NullableWrapperConverters.supportsUnwrapping(Future.class)).isFalse();
+		assertThat(NullableWrapperConverters.supportsUnwrapping(ListenableFuture.class)).isFalse();
+		assertThat(NullableWrapperConverters.supportsUnwrapping(Option.class)).isTrue();
+	}
+
+	@Test // DATACMNS-483, DATACMNS-1762
+	void turnsNullIntoGuavaOptional() {
+		assertThat(conversionService.convert(new NullableWrapper(null), Optional.class)).isEqualTo(Optional.absent());
+	}
+
+	@Test // DATACMNS-483, DATACMNS-1762
+	@SuppressWarnings("unchecked")
+	void turnsNullIntoJdk8Optional() {
+		assertThat(conversionService.convert(new NullableWrapper(null), java.util.Optional.class)).isEmpty();
+	}
+
+	@Test // DATACMNS-768, DATACMNS-1762
+	void unwrapsJdk8Optional() {
+		assertThat(NullableWrapperConverters.unwrap(java.util.Optional.of("Foo"))).isEqualTo("Foo");
+	}
+
+	@Test // DATACMNS-768, DATACMNS-1762
+	void unwrapsGuava8Optional() {
+		assertThat(NullableWrapperConverters.unwrap(Optional.of("Foo"))).isEqualTo("Foo");
+	}
+
+	@Test // DATACMNS-768, DATACMNS-1762
+	void unwrapsNullToNull() {
+		assertThat(NullableWrapperConverters.unwrap(null)).isNull();
+	}
+
+	@Test // DATACMNS-768, DATACMNS-1762
+	void unwrapsNonWrapperTypeToItself() {
+		assertThat(NullableWrapperConverters.unwrap("Foo")).isEqualTo("Foo");
+	}
+
+	@Test // DATACMNS-795, DATACMNS-1762
+	void turnsNullIntoScalaOptionEmpty() {
+		assertThat(conversionService.convert(new NullableWrapper(null), Option.class)).isEqualTo(Option.empty());
+	}
+
+	@Test // DATACMNS-795, DATACMNS-1762
+	void unwrapsScalaOption() {
+		assertThat(NullableWrapperConverters.unwrap(Option.apply("foo"))).isEqualTo("foo");
+	}
+
+	@Test // DATACMNS-874, DATACMNS-1762
+	void unwrapsEmptyScalaOption() {
+		assertThat(NullableWrapperConverters.unwrap(Option.empty())).isNull();
+	}
+
+	@Test // DATACMNS-1065, DATACMNS-1762
+	void unwrapsEmptyVavrOption() {
+		assertThat(NullableWrapperConverters.unwrap(io.vavr.control.Option.none())).isNull();
+	}
+
+	@Test // DATACMNS-1065, DATACMNS-1762
+	void unwrapsVavrOption() {
+		assertThat(NullableWrapperConverters.unwrap(io.vavr.control.Option.of("string"))).isEqualTo("string");
+	}
+
+}