string to collection and array converters now are conditional and apply target element type match

Author: Keith Donald

org.springframework.core/src/main/java/org/springframework/core/convert/ConversionService.java

@@ -27,7 +27,12 @@ public interface ConversionService {
 
 	/**
 	 * Returns true if objects of sourceType can be converted to targetType.
-	 * @param sourceType the source type to convert from (required)
+	 * If this method returns true, it means {@link #convert(Object, Class)} is capable of converting an instance of sourceType to targetType.
+	 * Special note on collections, arrays, and maps types:
+	 * For conversion between collection, array, and map types, this method will return 'true'
+	 * even though a convert invocation may still generate a {@link ConversionException} if the underlying elements are not convertible.
+	 * Callers are expected to handle this exceptional case when working with collections and maps.
+	 * @param sourceType the source type to convert from (may be null if source is null)
 	 * @param targetType the target type to convert to (required)
 	 * @return true if a conversion can be performed, false if not
 	 * @throws IllegalArgumentException if targetType is null
@@ -36,12 +41,16 @@ public interface ConversionService {
 
 	/**
 	 * Returns true if objects of sourceType can be converted to the targetType.
-	 * The TypeDescriptors provide additional context about the source and target locations where conversion would occur, often object property locations.
-	 * @param sourceType context about the source type to convert from (required)
+	 * The TypeDescriptors provide additional context about the source and target locations where conversion would occur, often object fields or property locations.
+	 * If this method returns true, it means {@link #convert(Object, TypeDescriptor, TypeDescriptor)} is capable of converting an instance of sourceType to targetType.
+	 * Special note on collections, arrays, and maps types:
+	 * For conversion between collection, array, and map types, this method will return 'true'
+	 * even though a convert invocation may still generate a {@link ConversionException} if the underlying elements are not convertible.
+	 * Callers are expected to handle this exceptional case when working with collections and maps.
+	 * @param sourceType context about the source type to convert from (may be null if source is null)
 	 * @param targetType context about the target type to convert to (required)
 	 * @return true if a conversion can be performed between the source and target types, false if not
 	 * @throws IllegalArgumentException if targetType is null
-	 * @see TypeDescriptor#forObject(Object)
 	 */
 	boolean canConvert(TypeDescriptor sourceType, TypeDescriptor targetType);
 
@@ -57,15 +66,14 @@ public interface ConversionService {
 
 	/**
 	 * Convert the source to targetType.
-	 * The TypeDescriptors provide additional context about the source and target locations where conversion will occur, often object property locations.
+	 * The TypeDescriptors provide additional context about the source and target locations where conversion will occur, often object fields or property locations.
 	 * @param source the source object to convert (may be null)
 	 * @param sourceType context about the source type converting from (may be null if source is null)
 	 * @param targetType context about the target type to convert to (required)
 	 * @return the converted object, an instance of {@link TypeDescriptor#getObjectType() targetType}</code>
 	 * @throws ConversionException if a conversion exception occurred
 	 * @throws IllegalArgumentException if targetType is null
 	 * @throws IllegalArgumentException if sourceType is null but source is not null
-	 * @see TypeDescriptor#forObject(Object)
 	 */
 	Object convert(Object source, TypeDescriptor sourceType, TypeDescriptor targetType);
 

org.springframework.core/src/main/java/org/springframework/core/convert/support/StringToArrayConverter.java

@@ -22,16 +22,17 @@
 
 import org.springframework.core.convert.ConversionService;
 import org.springframework.core.convert.TypeDescriptor;
-import org.springframework.core.convert.converter.GenericConverter;
+import org.springframework.core.convert.converter.ConditionalGenericConverter;
 import org.springframework.util.StringUtils;
 
 /**
  * Converts a comma-delimited String to an Array.
- *
+ * Only matches if String.class can be converted to the target array element type.
+ * 
  * @author Keith Donald
  * @since 3.0
  */
-final class StringToArrayConverter implements GenericConverter {
+final class StringToArrayConverter implements ConditionalGenericConverter {
 
 	private final ConversionService conversionService;
 
@@ -43,6 +44,10 @@ public Set<ConvertiblePair> getConvertibleTypes() {
 		return Collections.singleton(new ConvertiblePair(String.class, Object[].class));
 	}
 
+	public boolean matches(TypeDescriptor sourceType, TypeDescriptor targetType) {
+		return this.conversionService.canConvert(sourceType, targetType.getElementType());
+	}
+	
 	public Object convert(Object source, TypeDescriptor sourceType, TypeDescriptor targetType) {
 		if (source == null) {
 			return null;

org.springframework.core/src/main/java/org/springframework/core/convert/support/StringToCollectionConverter.java

@@ -28,6 +28,7 @@
 
 /**
  * Converts a comma-delimited String to a Collection.
+ * If the target collection element type is declared, only matches if String.class can be converted to it.
  *
  * @author Keith Donald
  * @since 3.0
@@ -45,10 +46,11 @@ public Set<ConvertiblePair> getConvertibleTypes() {
 	}
 
 	public boolean matches(TypeDescriptor sourceType, TypeDescriptor targetType) {
-		if (targetType.getElementType() == null) {
+		if (targetType.getElementType() != null) {
+			return this.conversionService.canConvert(sourceType, targetType.getElementType());
+		} else {
 			return true;
 		}
-		return this.conversionService.canConvert(sourceType, targetType.getElementType());
 	}
 
 	@SuppressWarnings("unchecked")

org.springframework.core/src/test/java/org/springframework/core/convert/support/DefaultConversionTests.java

@@ -759,4 +759,5 @@ public static TestEntity findTestEntity(Long id) {
 			return new TestEntity(id);
 		}
 	}
+	
 }

org.springframework.core/src/test/java/org/springframework/core/convert/support/GenericConversionServiceTests.java

@@ -16,16 +16,17 @@
 
 package org.springframework.core.convert.support;
 
+import static junit.framework.Assert.assertTrue;
 import static org.junit.Assert.assertEquals;
 import static org.junit.Assert.assertFalse;
 import static org.junit.Assert.assertNotNull;
 import static org.junit.Assert.assertNull;
 import static org.junit.Assert.assertSame;
-import static org.junit.Assert.assertTrue;
 import static org.junit.Assert.fail;
 
 import java.util.ArrayList;
 import java.util.Arrays;
+import java.util.Collection;
 import java.util.HashMap;
 import java.util.LinkedHashMap;
 import java.util.LinkedList;
@@ -528,4 +529,25 @@ public WithCopyConstructor(WithCopyConstructor value) {
 
 	public static Map<String, ?> wildcardMap;
 
+	@Test
+	public void stringToArrayCanConvert() {
+		conversionService.addConverter(new StringToArrayConverter(conversionService));
+		assertFalse(conversionService.canConvert(String.class, Integer[].class));
+		conversionService.addConverterFactory(new StringToNumberConverterFactory());
+		assertTrue(conversionService.canConvert(String.class, Integer[].class));
+	}
+	
+	@Test
+	public void stringToCollectionCanConvert() throws Exception {
+		conversionService.addConverter(new StringToCollectionConverter(conversionService));
+		assertTrue(conversionService.canConvert(String.class, Collection.class));
+		TypeDescriptor targetType = new TypeDescriptor(getClass().getField("stringToCollection"));
+		assertFalse(conversionService.canConvert(TypeDescriptor.valueOf(String.class), targetType));		
+		conversionService.addConverterFactory(new StringToNumberConverterFactory());
+		assertTrue(conversionService.canConvert(TypeDescriptor.valueOf(String.class), targetType));		
+	}
+	
+	public Collection<Integer> stringToCollection;
+	
+
 }