Add support for @Delimiter binding

Add a new `@Delimiter` annotation that can be used to change how a
String value is bound to a Collection.

Fixes gh-11883

spring-boot-project/spring-boot/src/main/java/org/springframework/boot/context/properties/bind/ArrayBinder.java

@@ -41,7 +41,7 @@ class ArrayBinder extends IndexedElementsBinder<Object> {
 		IndexedCollectionSupplier result = new IndexedCollectionSupplier(ArrayList::new);
 		ResolvableType aggregateType = target.getType();
 		ResolvableType elementType = target.getType().getComponentType();
-		bindIndexed(name, elementBinder, aggregateType, elementType, result);
+		bindIndexed(name, target, elementBinder, aggregateType, elementType, result);
 		if (result.wasSupplied()) {
 			List<Object> list = (List<Object>) result.get();
 			Object array = Array.newInstance(elementType.resolve(), list.size());

spring-boot-project/spring-boot/src/main/java/org/springframework/boot/context/properties/bind/CollectionBinder.java

@@ -45,7 +45,7 @@ class CollectionBinder extends IndexedElementsBinder<Collection<Object>> {
 		ResolvableType elementType = target.getType().asCollection().getGeneric();
 		IndexedCollectionSupplier result = new IndexedCollectionSupplier(
 				() -> CollectionFactory.createCollection(collectionType, 0));
-		bindIndexed(name, elementBinder, aggregateType, elementType, result);
+		bindIndexed(name, target, elementBinder, aggregateType, elementType, result);
 		if (result.wasSupplied()) {
 			return result.get();
 		}

spring-boot-project/spring-boot/src/main/java/org/springframework/boot/context/properties/bind/IndexedElementsBinder.java

@@ -16,6 +16,7 @@
 
 package org.springframework.boot.context.properties.bind;
 
+import java.lang.annotation.Annotation;
 import java.util.Collection;
 import java.util.List;
 import java.util.TreeSet;
@@ -56,16 +57,18 @@ abstract class IndexedElementsBinder<T> extends AggregateBinder<T> {
 	/**
 	 * Bind indexed elements to the supplied collection.
 	 * @param name The name of the property to bind
+	 * @param target the target bindable
 	 * @param elementBinder the binder to use for elements
 	 * @param aggregateType the aggregate type, may be a collection or an array
 	 * @param elementType the element type
 	 * @param result the destination for results
 	 */
-	protected final void bindIndexed(ConfigurationPropertyName name,
+	protected final void bindIndexed(ConfigurationPropertyName name, Bindable<?> target,
 			AggregateElementBinder elementBinder, ResolvableType aggregateType,
 			ResolvableType elementType, IndexedCollectionSupplier result) {
 		for (ConfigurationPropertySource source : getContext().getSources()) {
-			bindIndexed(source, name, elementBinder, result, aggregateType, elementType);
+			bindIndexed(source, name, target, elementBinder, result, aggregateType,
+					elementType);
 			if (result.wasSupplied() && result.get() != null) {
 				return;
 			}
@@ -73,12 +76,13 @@ abstract class IndexedElementsBinder<T> extends AggregateBinder<T> {
 	}
 
 	private void bindIndexed(ConfigurationPropertySource source,
-			ConfigurationPropertyName root, AggregateElementBinder elementBinder,
-			IndexedCollectionSupplier collection, ResolvableType aggregateType,
-			ResolvableType elementType) {
+			ConfigurationPropertyName root, Bindable<?> target,
+			AggregateElementBinder elementBinder, IndexedCollectionSupplier collection,
+			ResolvableType aggregateType, ResolvableType elementType) {
 		ConfigurationProperty property = source.getConfigurationProperty(root);
 		if (property != null) {
-			Object aggregate = convert(property.getValue(), aggregateType);
+			Object aggregate = convert(property.getValue(), aggregateType,
+					target.getAnnotations());
 			ResolvableType collectionType = forClassWithGenerics(
 					collection.get().getClass(), elementType);
 			Collection<Object> elements = convert(aggregate, collectionType);
@@ -134,10 +138,11 @@ abstract class IndexedElementsBinder<T> extends AggregateBinder<T> {
 		}
 	}
 
-	private <C> C convert(Object value, ResolvableType type) {
+	private <C> C convert(Object value, ResolvableType type, Annotation... annotations) {
 		value = getContext().getPlaceholdersResolver().resolvePlaceholders(value);
 		BinderConversionService conversionService = getContext().getConversionService();
-		return ResolvableTypeDescriptor.forType(type).convert(conversionService, value);
+		return ResolvableTypeDescriptor.forType(type, annotations)
+				.convert(conversionService, value);
 	}
 
 	// Work around for SPR-16456

spring-boot-project/spring-boot/src/main/java/org/springframework/boot/context/properties/bind/convert/BinderConversionService.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2012-2017 the original author or authors.
+ * Copyright 2012-2018 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.
@@ -16,14 +16,17 @@
 
 package org.springframework.boot.context.properties.bind.convert;
 
+import java.util.ArrayList;
+import java.util.Collections;
+import java.util.List;
 import java.util.function.Function;
 
 import org.springframework.boot.context.properties.bind.Binder;
 import org.springframework.core.convert.ConversionException;
 import org.springframework.core.convert.ConversionService;
-import org.springframework.core.convert.ConverterNotFoundException;
 import org.springframework.core.convert.TypeDescriptor;
 import org.springframework.core.convert.support.DefaultConversionService;
+import org.springframework.core.convert.support.GenericConversionService;
 import org.springframework.format.annotation.DateTimeFormat;
 import org.springframework.format.datetime.DateFormatter;
 import org.springframework.format.datetime.DateFormatterRegistrar;
@@ -38,69 +41,30 @@ import org.springframework.format.support.DefaultFormattingConversionService;
  */
 public class BinderConversionService implements ConversionService {
 
-	private static final ConversionService additionalConversionService = createAdditionalConversionService();
-
 	private static final ConversionService defaultConversionService = new DefaultFormattingConversionService();
 
-	private final ConversionService conversionService;
+	private final List<ConversionService> conversionServices;
 
 	/**
 	 * Create a new {@link BinderConversionService} instance.
 	 * @param conversionService and option root conversion service
 	 */
 	public BinderConversionService(ConversionService conversionService) {
-		this.conversionService = (conversionService != null ? conversionService
-				: defaultConversionService);
+		List<ConversionService> conversionServices = new ArrayList<>();
+		conversionServices.add(createOverrideConversionService());
+		conversionServices.add(
+				conversionService != null ? conversionService : defaultConversionService);
+		conversionServices.add(createAdditionalConversionService());
+		this.conversionServices = Collections.unmodifiableList(conversionServices);
 	}
 
-	@Override
-	public boolean canConvert(Class<?> sourceType, Class<?> targetType) {
-		return (this.conversionService != null
-				&& this.conversionService.canConvert(sourceType, targetType))
-				|| additionalConversionService.canConvert(sourceType, targetType);
+	private ConversionService createOverrideConversionService() {
+		GenericConversionService service = new GenericConversionService();
+		service.addConverter(new DelimitedStringToCollectionConverter(this));
+		return service;
 	}
 
-	@Override
-	public boolean canConvert(TypeDescriptor sourceType, TypeDescriptor targetType) {
-		return (this.conversionService != null
-				&& this.conversionService.canConvert(sourceType, targetType))
-				|| additionalConversionService.canConvert(sourceType, targetType);
-	}
-
-	@Override
-	public <T> T convert(Object source, Class<T> targetType) {
-		return callConversionService((c) -> c.convert(source, targetType));
-	}
-
-	@Override
-	public Object convert(Object source, TypeDescriptor sourceType,
-			TypeDescriptor targetType) {
-		return callConversionService((c) -> c.convert(source, sourceType, targetType));
-	}
-
-	private <T> T callConversionService(Function<ConversionService, T> call) {
-		if (this.conversionService == null) {
-			return callAdditionalConversionService(call, null);
-		}
-		try {
-			return call.apply(this.conversionService);
-		}
-		catch (ConversionException ex) {
-			return callAdditionalConversionService(call, ex);
-		}
-	}
-
-	private <T> T callAdditionalConversionService(Function<ConversionService, T> call,
-			RuntimeException cause) {
-		try {
-			return call.apply(additionalConversionService);
-		}
-		catch (ConverterNotFoundException ex) {
-			throw (cause != null ? cause : ex);
-		}
-	}
-
-	private static ConversionService createAdditionalConversionService() {
+	private ConversionService createAdditionalConversionService() {
 		DefaultFormattingConversionService service = new DefaultFormattingConversionService();
 		DefaultConversionService.addCollectionConverters(service);
 		service.addConverterFactory(new StringToEnumConverterFactory());
@@ -117,4 +81,48 @@ public class BinderConversionService implements ConversionService {
 		return service;
 	}
 
+	@Override
+	public boolean canConvert(Class<?> sourceType, Class<?> targetType) {
+		for (ConversionService service : this.conversionServices) {
+			if (service.canConvert(sourceType, targetType)) {
+				return true;
+			}
+		}
+		return false;
+	}
+
+	@Override
+	public boolean canConvert(TypeDescriptor sourceType, TypeDescriptor targetType) {
+		for (ConversionService service : this.conversionServices) {
+			if (service.canConvert(sourceType, targetType)) {
+				return true;
+			}
+		}
+		return false;
+	}
+
+	@Override
+	public <T> T convert(Object source, Class<T> targetType) {
+		return callConversionServices((c) -> c.convert(source, targetType));
+	}
+
+	@Override
+	public Object convert(Object source, TypeDescriptor sourceType,
+			TypeDescriptor targetType) {
+		return callConversionServices((c) -> c.convert(source, sourceType, targetType));
+	}
+
+	private <T> T callConversionServices(Function<ConversionService, T> call) {
+		ConversionException exception = null;
+		for (ConversionService service : this.conversionServices) {
+			try {
+				return call.apply(service);
+			}
+			catch (ConversionException ex) {
+				exception = ex;
+			}
+		}
+		throw exception;
+	}
+
 }

spring-boot-project/spring-boot/src/main/java/org/springframework/boot/context/properties/bind/convert/DelimitedStringToCollectionConverter.java

@@ -0,0 +1,98 @@
+/*
+ * Copyright 2012-2018 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
+ *
+ *      http://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.boot.context.properties.bind.convert;
+
+import java.util.Arrays;
+import java.util.Collection;
+import java.util.Collections;
+import java.util.Set;
+import java.util.stream.Stream;
+
+import org.springframework.core.CollectionFactory;
+import org.springframework.core.convert.ConversionService;
+import org.springframework.core.convert.TypeDescriptor;
+import org.springframework.core.convert.converter.ConditionalGenericConverter;
+import org.springframework.lang.Nullable;
+import org.springframework.util.Assert;
+import org.springframework.util.StringUtils;
+
+/**
+ * Converts a {@link Delimiter delimited} String to a Collection.
+ *
+ * @author Phillip Webb
+ */
+class DelimitedStringToCollectionConverter implements ConditionalGenericConverter {
+
+	private final ConversionService conversionService;
+
+	DelimitedStringToCollectionConverter(ConversionService conversionService) {
+		Assert.notNull(conversionService, "ConversionService must not be null");
+		this.conversionService = conversionService;
+	}
+
+	@Override
+	public Set<ConvertiblePair> getConvertibleTypes() {
+		return Collections.singleton(new ConvertiblePair(String.class, Collection.class));
+	}
+
+	@Override
+	public boolean matches(TypeDescriptor sourceType, TypeDescriptor targetType) {
+		return targetType.hasAnnotation(Delimiter.class)
+				&& (targetType.getElementTypeDescriptor() == null
+						|| this.conversionService.canConvert(sourceType,
+								targetType.getElementTypeDescriptor()));
+	}
+
+	@Override
+	@Nullable
+	public Object convert(@Nullable Object source, TypeDescriptor sourceType,
+			TypeDescriptor targetType) {
+		if (source == null) {
+			return null;
+		}
+		return convert((String) source, sourceType, targetType);
+	}
+
+	private Object convert(String source, TypeDescriptor sourceType,
+			TypeDescriptor targetType) {
+		Delimiter delimiter = targetType.getAnnotation(Delimiter.class);
+		Assert.state(delimiter != null, "Missing @DelimitedStringFormat annotation");
+		String[] elements = getElements(source, delimiter.value());
+		TypeDescriptor elementDescriptor = targetType.getElementTypeDescriptor();
+		Collection<Object> target = createCollection(targetType, elementDescriptor,
+				elements.length);
+		Stream<Object> stream = Arrays.stream(elements).map(String::trim);
+		if (elementDescriptor != null) {
+			stream = stream.map((element) -> this.conversionService.convert(element,
+					sourceType, elementDescriptor));
+		}
+		stream.forEach(target::add);
+		return target;
+	}
+
+	private Collection<Object> createCollection(TypeDescriptor targetType,
+			TypeDescriptor elementDescriptor, int length) {
+		return CollectionFactory.createCollection(targetType.getType(),
+				(elementDescriptor != null ? elementDescriptor.getType() : null), length);
+	}
+
+	private String[] getElements(String source, String delimiter) {
+		return StringUtils.delimitedListToStringArray(source,
+				Delimiter.NONE.equals(delimiter) ? null : delimiter);
+	}
+
+}

spring-boot-project/spring-boot/src/main/java/org/springframework/boot/context/properties/bind/convert/Delimiter.java

@@ -0,0 +1,51 @@
+/*
+ * Copyright 2012-2018 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
+ *
+ *      http://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.boot.context.properties.bind.convert;
+
+import java.lang.annotation.Documented;
+import java.lang.annotation.ElementType;
+import java.lang.annotation.Retention;
+import java.lang.annotation.RetentionPolicy;
+import java.lang.annotation.Target;
+
+/**
+ * Declares a field or method parameter should be converted to collection using the
+ * specified delimiter.
+ *
+ * @author Phillip Webb
+ * @since 2.0.0
+ */
+@Documented
+@Retention(RetentionPolicy.RUNTIME)
+@Target({ ElementType.METHOD, ElementType.FIELD, ElementType.PARAMETER,
+		ElementType.ANNOTATION_TYPE })
+public @interface Delimiter {
+
+	/**
+	 * A delimiter value used to indicate that no delimiter is required and the result
+	 * should be a single element containing the entire string.
+	 */
+	String NONE = "";
+
+	/**
+	 * The delimiter to use or {@code NONE} if the entire contents should be treated as a
+	 * single element.
+	 * @return the delimiter
+	 */
+	String value();
+
+}

spring-boot-project/spring-boot/src/test/java/org/springframework/boot/context/properties/bind/JavaBeanBinderTests.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2012-2017 the original author or authors.
+ * Copyright 2012-2018 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.
@@ -31,6 +31,7 @@ import org.junit.Rule;
 import org.junit.Test;
 import org.junit.rules.ExpectedException;
 
+import org.springframework.boot.context.properties.bind.convert.Delimiter;
 import org.springframework.boot.context.properties.bind.handler.IgnoreErrorsBindHandler;
 import org.springframework.boot.context.properties.source.ConfigurationPropertyName;
 import org.springframework.boot.context.properties.source.ConfigurationPropertySource;
@@ -210,6 +211,17 @@ public class JavaBeanBinderTests {
 				ExampleEnum.BAR_BAZ);
 	}
 
+	@Test
+	public void bindToClassShouldBindToCollectionWithDelimeter() {
+		MockConfigurationPropertySource source = new MockConfigurationPropertySource();
+		source.put("foo.collection", "foo-bar|bar-baz");
+		this.sources.add(source);
+		ExampleCollectionBeanWithDelimeter bean = this.binder
+				.bind("foo", Bindable.of(ExampleCollectionBeanWithDelimeter.class)).get();
+		assertThat(bean.getCollection()).containsExactly(ExampleEnum.FOO_BAR,
+				ExampleEnum.BAR_BAZ);
+	}
+
 	@Test
 	public void bindToClassWhenHasNoSetterShouldBindToMap() {
 		MockConfigurationPropertySource source = new MockConfigurationPropertySource();
@@ -617,6 +629,21 @@ public class JavaBeanBinderTests {
 
 	}
 
+	public static class ExampleCollectionBeanWithDelimeter {
+
+		@Delimiter("|")
+		private Collection<ExampleEnum> collection;
+
+		public Collection<ExampleEnum> getCollection() {
+			return this.collection;
+		}
+
+		public void setCollection(Collection<ExampleEnum> collection) {
+			this.collection = collection;
+		}
+
+	}
+
 	public static class ExampleNestedBean {
 
 		private ExampleValueBean valueBean;

spring-boot-project/spring-boot/src/test/java/org/springframework/boot/context/properties/bind/convert/BinderConversionServiceTests.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2012-2017 the original author or authors.
+ * Copyright 2012-2018 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.
@@ -19,6 +19,7 @@ package org.springframework.boot.context.properties.bind.convert;
 import java.io.InputStream;
 import java.net.InetAddress;
 import java.time.Duration;
+import java.util.List;
 
 import org.junit.Before;
 import org.junit.Test;
@@ -27,6 +28,7 @@ import org.springframework.core.convert.ConversionFailedException;
 import org.springframework.core.convert.ConversionService;
 import org.springframework.core.convert.TypeDescriptor;
 import org.springframework.core.io.Resource;
+import org.springframework.util.ReflectionUtils;
 
 import static org.assertj.core.api.Assertions.assertThat;
 import static org.mockito.BDDMockito.given;
@@ -166,6 +168,36 @@ public class BinderConversionServiceTests {
 		assertThat(converted).isEqualTo(Duration.ofMillis(10));
 	}
 
+	@Test
+	@SuppressWarnings("unchecked")
+	public void conversionServiceShouldSupportBarDelimitedStrings() {
+		this.service = new BinderConversionService(null);
+		List<TestEnum> converted = (List<TestEnum>) this.service.convert("ONE|ONE|TWO",
+				TypeDescriptor.valueOf(String.class), TypeDescriptor.nested(
+						ReflectionUtils.findField(DelimitedValues.class, "bar"), 0));
+		assertThat(converted).containsExactly(TestEnum.ONE, TestEnum.ONE, TestEnum.TWO);
+	}
+
+	@Test
+	@SuppressWarnings("unchecked")
+	public void conversionServiceShouldSupportNoneDelimitedStrings() {
+		this.service = new BinderConversionService(null);
+		List<String> converted = (List<String>) this.service.convert("a,b,c",
+				TypeDescriptor.valueOf(String.class), TypeDescriptor.nested(
+						ReflectionUtils.findField(DelimitedValues.class, "none"), 0));
+		assertThat(converted).containsExactly("a,b,c");
+	}
+
+	static class DelimitedValues {
+
+		@Delimiter("|")
+		List<TestEnum> bar;
+
+		@Delimiter(Delimiter.NONE)
+		List<String> none;
+
+	}
+
 	enum TestEnum {
 
 		ONE, TWO

spring-boot-project/spring-boot/src/test/java/org/springframework/boot/context/properties/bind/convert/DelimitedStringToCollectionConverterTests.java

@@ -0,0 +1,178 @@
+/*
+ * Copyright 2012-2018 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
+ *
+ *      http://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.boot.context.properties.bind.convert;
+
+import java.util.Collection;
+import java.util.LinkedList;
+import java.util.List;
+import java.util.Set;
+
+import org.junit.Before;
+import org.junit.Rule;
+import org.junit.Test;
+import org.junit.rules.ExpectedException;
+
+import org.springframework.core.convert.TypeDescriptor;
+import org.springframework.core.convert.converter.GenericConverter.ConvertiblePair;
+import org.springframework.format.support.DefaultFormattingConversionService;
+import org.springframework.util.ReflectionUtils;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+/**
+ * Tests for {@link DelimitedStringToCollectionConverter}.
+ *
+ * @author Phillip Webb
+ */
+public class DelimitedStringToCollectionConverterTests {
+
+	private DefaultFormattingConversionService service;
+
+	private DelimitedStringToCollectionConverter converter;
+
+	@Rule
+	public ExpectedException thrown = ExpectedException.none();
+
+	@Before
+	public void setup() {
+		this.service = new DefaultFormattingConversionService(null, false);
+		this.converter = new DelimitedStringToCollectionConverter(this.service);
+		this.service.addConverter(this.converter);
+		DefaultFormattingConversionService.addDefaultFormatters(this.service);
+	}
+
+	@Test
+	public void createWhenConversionServiceIsNullShouldThrowException() {
+		this.thrown.expect(IllegalArgumentException.class);
+		this.thrown.expectMessage("ConversionService must not be null");
+		new DelimitedStringToCollectionConverter(null);
+	}
+
+	@Test
+	public void getConvertiblePairShouldReturnStringCollectionPair() {
+		Set<ConvertiblePair> types = this.converter.getConvertibleTypes();
+		assertThat(types).hasSize(1);
+		ConvertiblePair pair = types.iterator().next();
+		assertThat(pair.getSourceType()).isEqualTo(String.class);
+		assertThat(pair.getTargetType()).isEqualTo(Collection.class);
+	}
+
+	@Test
+	public void matchesWhenTargetIsNotAnnotatedShouldReturnFalse() {
+		TypeDescriptor sourceType = TypeDescriptor.valueOf(String.class);
+		TypeDescriptor targetType = TypeDescriptor
+				.nested(ReflectionUtils.findField(Values.class, "noAnnotation"), 0);
+		assertThat(this.converter.matches(sourceType, targetType)).isFalse();
+	}
+
+	@Test
+	public void matchesWhenHasAnnotationAndNoElementTypeShouldReturnTrue() {
+		TypeDescriptor sourceType = TypeDescriptor.valueOf(String.class);
+		TypeDescriptor targetType = TypeDescriptor
+				.nested(ReflectionUtils.findField(Values.class, "noElementType"), 0);
+		assertThat(this.converter.matches(sourceType, targetType)).isTrue();
+	}
+
+	@Test
+	public void matchesWhenHasAnnotationAndConvertibleElementTypeShouldReturnTrue() {
+		TypeDescriptor sourceType = TypeDescriptor.valueOf(String.class);
+		TypeDescriptor targetType = TypeDescriptor.nested(
+				ReflectionUtils.findField(Values.class, "convertibleElementType"), 0);
+		assertThat(this.converter.matches(sourceType, targetType)).isTrue();
+	}
+
+	@Test
+	public void matchesWhenHasAnnotationAndNonConvertibleElementTypeShouldReturnFalse() {
+		TypeDescriptor sourceType = TypeDescriptor.valueOf(String.class);
+		TypeDescriptor targetType = TypeDescriptor.nested(
+				ReflectionUtils.findField(Values.class, "nonConvertibleElementType"), 0);
+		assertThat(this.converter.matches(sourceType, targetType)).isFalse();
+	}
+
+	@Test
+	@SuppressWarnings("unchecked")
+	public void convertWhenHasNoElementTypeShouldReturnTrimmedString() {
+		TypeDescriptor sourceType = TypeDescriptor.valueOf(String.class);
+		TypeDescriptor targetType = TypeDescriptor
+				.nested(ReflectionUtils.findField(Values.class, "noElementType"), 0);
+		List<String> converted = (List<String>) this.converter.convert(" a |  b| c  ",
+				sourceType, targetType);
+		assertThat(converted).containsExactly("a", "b", "c");
+	}
+
+	@Test
+	@SuppressWarnings("unchecked")
+	public void convertWhenHasConvertibleElementTypeShouldReturnConvertedType() {
+		TypeDescriptor sourceType = TypeDescriptor.valueOf(String.class);
+		TypeDescriptor targetType = TypeDescriptor.nested(
+				ReflectionUtils.findField(Values.class, "convertibleElementType"), 0);
+		List<Integer> converted = (List<Integer>) this.converter.convert(" 1 |  2| 3  ",
+				sourceType, targetType);
+		assertThat(converted).containsExactly(1, 2, 3);
+	}
+
+	@Test
+	@SuppressWarnings("unchecked")
+	public void convertWhenHasDelimiterOfNoneShouldReturnTrimmedStringElement() {
+		TypeDescriptor sourceType = TypeDescriptor.valueOf(String.class);
+		TypeDescriptor targetType = TypeDescriptor
+				.nested(ReflectionUtils.findField(Values.class, "delimiterNone"), 0);
+		List<String> converted = (List<String>) this.converter.convert("a,b,c",
+				sourceType, targetType);
+		assertThat(converted).containsExactly("a,b,c");
+	}
+
+	@Test
+	public void convertWhenHasCollectionObjectTypeShouldUseCollectionObjectType() {
+		TypeDescriptor sourceType = TypeDescriptor.valueOf(String.class);
+		TypeDescriptor targetType = TypeDescriptor
+				.nested(ReflectionUtils.findField(Values.class, "specificType"), 0);
+		Object converted = this.converter.convert("a*b", sourceType, targetType);
+		assertThat(converted).isInstanceOf(MyCustomList.class);
+	}
+
+	static class Values {
+
+		List<String> noAnnotation;
+
+		@SuppressWarnings("rawtypes")
+		@Delimiter("|")
+		List noElementType;
+
+		@Delimiter("|")
+		List<Integer> convertibleElementType;
+
+		@Delimiter("|")
+		List<NonConvertible> nonConvertibleElementType;
+
+		@Delimiter(Delimiter.NONE)
+		List<String> delimiterNone;
+
+		@Delimiter("*")
+		MyCustomList<String> specificType;
+
+	}
+
+	static class NonConvertible {
+
+	}
+
+	static class MyCustomList<E> extends LinkedList<E> {
+
+	}
+
+}