Allow TypeDescriptor array construction

Add a static factory method that can be used to create an array
TypeDescriptor with a specific element type. Allows array types
with generic elements to be constructed.

Issue: SPR-9792

Author: philwebb

spring-core/src/main/java/org/springframework/core/convert/TypeDescriptor.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2012 the original author or authors.
+ * Copyright 2002-2013 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.
@@ -17,6 +17,7 @@
 package org.springframework.core.convert;
 
 import java.lang.annotation.Annotation;
+import java.lang.reflect.Array;
 import java.lang.reflect.Field;
 import java.util.Collection;
 import java.util.HashMap;
@@ -33,6 +34,7 @@
  * @author Keith Donald
  * @author Andy Clement
  * @author Juergen Hoeller
+ * @author Phillip Webb
  * @since 3.0
  */
 public class TypeDescriptor {
@@ -146,6 +148,22 @@ public static TypeDescriptor map(Class<?> mapType, TypeDescriptor keyTypeDescrip
 		return new TypeDescriptor(mapType, keyTypeDescriptor, valueTypeDescriptor);
 	}
 
+	/**
+	 * Create a new type descriptor as an array of the specified type. For example to
+	 * create a {@code Map<String,String>[]} use
+	 * {@code TypeDescriptor.array(TypeDescriptor.map(Map.class, TypeDescriptor.value(String.class), TypeDescriptor.value(String.class)))}.
+	 * @param elementTypeDescriptor the {@link TypeDescriptor} of the array element or {@code null}
+	 * @return an array {@link TypeDescriptor} or {@code null} if {@code elementTypeDescriptor} is {@code null}
+	 * @since 3.2
+	 */
+	public static TypeDescriptor array(TypeDescriptor elementTypeDescriptor) {
+		if(elementTypeDescriptor == null) {
+			return null;
+		}
+		Class<?> type = Array.newInstance(elementTypeDescriptor.getType(), 0).getClass();
+		return new TypeDescriptor(type, elementTypeDescriptor, null, null, elementTypeDescriptor.getAnnotations());
+	}
+
 	/**
 	 * Creates a type descriptor for a nested type declared within the method parameter.
 	 * For example, if the methodParameter is a List&lt;String&gt; and the nestingLevel is 1, the nested type descriptor will be String.class.

spring-core/src/test/java/org/springframework/core/convert/TypeDescriptorTests.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2012 the original author or authors.
+ * Copyright 2002-2013 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.
@@ -25,6 +25,7 @@
 import java.util.Date;
 import java.util.HashMap;
 import java.util.HashSet;
+import java.util.LinkedHashMap;
 import java.util.List;
 import java.util.Map;
 
@@ -36,6 +37,7 @@
 /**
  * @author Keith Donald
  * @author Andy Clement
+ * @author Phillip Webb
  */
 @SuppressWarnings("rawtypes")
 public class TypeDescriptorTests {
@@ -849,4 +851,23 @@ class CustomMap extends HashMap<String, Integer> {
 		assertEquals(TypeDescriptor.forObject(new CustomMap()).getMapValueTypeDescriptor(), TypeDescriptor.valueOf(Integer.class));
 	}
 
+	@Test
+	public void createMapArray() throws Exception {
+		TypeDescriptor mapType = TypeDescriptor.map(LinkedHashMap.class, TypeDescriptor.valueOf(String.class), TypeDescriptor.valueOf(Integer.class));
+		TypeDescriptor arrayType = TypeDescriptor.array(mapType);
+		assertEquals(arrayType.getType(), LinkedHashMap[].class);
+		assertEquals(arrayType.getElementTypeDescriptor(), mapType);
+	}
+
+
+	@Test
+	public void createStringArray() throws Exception {
+		TypeDescriptor arrayType = TypeDescriptor.array(TypeDescriptor.valueOf(String.class));
+		assertEquals(arrayType, TypeDescriptor.valueOf(String[].class));
+	}
+
+	@Test
+	public void createNullArray() throws Exception {
+		assertNull(TypeDescriptor.array(null));
+	}
 }