From 57b6c557838b01929b8f133a99a74ed0ddc6bd18 Mon Sep 17 00:00:00 2001
From: lucve <luc.veldhuis@adyen.com>
Date: Tue, 26 Aug 2025 09:40:25 +0200
Subject: [PATCH] Issue#69 | Add ResolvedTypeMapper to convert ResolvedType
 into Type

---
 .../classmate/ResolvedTypeMapper.java         | 209 ++++++++++++++
 .../classmate/TestResolvedTypeMapper.java     | 267 ++++++++++++++++++
 2 files changed, 476 insertions(+)
 create mode 100644 src/main/java/com/fasterxml/classmate/ResolvedTypeMapper.java
 create mode 100644 src/test/java/com/fasterxml/classmate/TestResolvedTypeMapper.java

diff --git a/src/main/java/com/fasterxml/classmate/ResolvedTypeMapper.java b/src/main/java/com/fasterxml/classmate/ResolvedTypeMapper.java
new file mode 100644
index 0000000..db66d33
--- /dev/null
+++ b/src/main/java/com/fasterxml/classmate/ResolvedTypeMapper.java
@@ -0,0 +1,209 @@
+package com.fasterxml.classmate;
+
+import com.fasterxml.classmate.types.ResolvedArrayType;
+import com.fasterxml.classmate.types.ResolvedRecursiveType;
+
+import java.io.Serializable;
+import java.lang.reflect.GenericArrayType;
+import java.lang.reflect.ParameterizedType;
+import java.lang.reflect.Type;
+import java.util.ArrayList;
+import java.util.Arrays;
+import java.util.List;
+import java.util.Objects;
+import java.util.stream.Collectors;
+
+
+/**
+ * Utility for converting a {@link ResolvedType} into a standard Java {@link Type}
+ * that can be used with the reflection API.
+ *
+ * <p><strong>Limitations:</strong></p>
+ * <ul>
+ *   <li><b>Type variables and wildcards are not fully supported.</b>
+ *       Since {@link ResolvedType} does not preserve full type variable or wildcard details,
+ *       this mapper resolves them to their <em>upper bound</em> (or {@link Object} if no upper bound is known).</li>
+ *   <li>For example:
+ *     <ul>
+ *       <li>A field declared as {@code E extends List} will map to {@code List} when the type is unbound.</li>
+ *       <li>A wildcard like {@code ? super List} or a type variable like {@code E super List} will map to {@code Object}.</li>
+ *       <li>If a concrete type binding is provided in the {@link TypeBindings},
+ *           for example {@code E extends List} bound to {@code ArrayList},
+ *           this mapper will return {@code ArrayList}.</li>
+ *     </ul>
+ *   </li>
+ * </ul>
+ *
+ * <p>
+ * For further discussion, see
+ * <a href="https://github.com/FasterXML/java-classmate/issues/69">issue #69</a>.
+ * </p>
+ */
+
+@SuppressWarnings("serial")
+public class ResolvedTypeMapper implements Serializable {
+
+	private static final long serialVersionUID = 1L;
+
+	/**
+	 * Method for mapping {@link ResolvedType} to java types.
+
+	 * @param resolvedType The resolved type to map to a java {@link Type}
+	 * @return The type with all generics resolved, OR with the generics replaced with the upper bounds AND with all wildcards resolved to the upper bound.
+	 */
+	public Type map(ResolvedType resolvedType) {
+		if (resolvedType instanceof ResolvedArrayType) {
+			ResolvedArrayType arrayType = (ResolvedArrayType) resolvedType;
+			ResolvedType arrayElementType = arrayType.getArrayElementType();
+			if (arrayElementType == null) {
+				throw new IllegalStateException("Missing array element type");
+			}
+			Type elementType = map(arrayElementType);
+			//GenericArrayType is only used for parameterized types or TypeVariables, but we don't have TypeVariables
+			if (elementType instanceof ParameterizedType) {
+				return new GenericArrayTypeImpl(elementType);
+			}
+			return arrayType.getErasedType();
+		}
+		// Extract recursive type
+		if (resolvedType instanceof ResolvedRecursiveType) {
+			ResolvedRecursiveType recursiveType = (ResolvedRecursiveType) resolvedType;
+			ResolvedType selfReferencedType = recursiveType.getSelfReferencedType();
+			if (selfReferencedType == null) {
+				throw new IllegalStateException("Missing self referenced type");
+			}
+			return map(selfReferencedType);
+		}
+		// no generics present, so the erased type is equal to the real type
+		if (resolvedType.getTypeParameters() == null || resolvedType.getTypeParameters().isEmpty()) {
+			return resolvedType.getErasedType();
+		}
+		// Parameters are present, so we need to create a parameterized
+		// Wildcard types are not supported, since we store the upperbound
+		return _mapParameterizedType(resolvedType);
+	}
+
+	private ParameterizedTypeImpl _mapParameterizedType(ResolvedType objectType) {
+		Class<?> erasedType = objectType.getErasedType();
+		List<Type> list = new ArrayList<>();
+		for (ResolvedType resolvedType : objectType.getTypeParameters()) {
+			Type mappedArrayType = map(resolvedType);
+			list.add(mappedArrayType);
+		}
+		return new ParameterizedTypeImpl(erasedType, list.toArray(new Type[0]), erasedType.getEnclosingClass());
+	}
+
+	/**
+	 * Implementation of ParameterizedType for classmate type creation
+	 */
+	static final class ParameterizedTypeImpl implements ParameterizedType {
+		private final Type rawType;
+		private final Type[] actualTypeArguments;
+		private final Type ownerType;
+
+		private ParameterizedTypeImpl(Type rawType, Type[] actualTypeArguments, Type ownerType) {
+			this.rawType = rawType;
+			this.actualTypeArguments = actualTypeArguments;
+			this.ownerType = ownerType;
+		}
+
+		/**
+		 * {@inheritDoc}
+		 */
+		@Override
+		public Type[] getActualTypeArguments() {
+			return actualTypeArguments;
+		}
+
+		/**
+		 * {@inheritDoc}
+		 */
+		@Override
+		public Type getRawType() {
+			return rawType;
+		}
+
+		/**
+		 * {@inheritDoc}
+		 */
+		@Override
+		public Type getOwnerType() {
+			return ownerType;
+		}
+
+		/**
+		 * {@inheritDoc}
+		 */
+		@Override
+		public boolean equals(Object o) {
+			if (!(o instanceof ParameterizedType)) {
+				return false;
+			}
+			ParameterizedType that = (ParameterizedType) o;
+			return Objects.equals(rawType, that.getRawType()) && Objects.deepEquals(actualTypeArguments, that.getActualTypeArguments()) && Objects.equals(ownerType, that.getOwnerType());
+		}
+
+		/**
+		 * {@inheritDoc}
+		 */
+		@Override
+		public int hashCode() {
+			return Objects.hash(rawType, Arrays.hashCode(actualTypeArguments), ownerType);
+		}
+
+		/**
+		 * {@inheritDoc}
+		 */
+		@Override
+		public String toString() {
+			return rawType + "<" + Arrays.stream(actualTypeArguments).map(Type::getTypeName).collect(Collectors.joining(", ")) + ">";
+		}
+	}
+
+	/**
+	 * Implementation of GenericArrayType for classmate type creation
+	 */
+	static final class GenericArrayTypeImpl implements GenericArrayType {
+		private final Type genericComponentType;
+
+		private GenericArrayTypeImpl(Type genericComponentType) {
+			this.genericComponentType = genericComponentType;
+		}
+
+		/**
+		 * {@inheritDoc}
+		 */
+		@Override
+		public Type getGenericComponentType() {
+			return genericComponentType;
+		}
+
+		/**
+		 * {@inheritDoc}
+		 */
+		@Override
+		public boolean equals(Object o) {
+			if (!(o instanceof GenericArrayType)) {
+				return false;
+			}
+			GenericArrayType that = (GenericArrayType) o;
+			return Objects.equals(genericComponentType, that.getGenericComponentType());
+		}
+
+		/**
+		 * {@inheritDoc}
+		 */
+		@Override
+		public int hashCode() {
+			return Objects.hashCode(genericComponentType);
+		}
+
+		/**
+		 * {@inheritDoc}
+		 */
+		@Override
+		public String toString() {
+			return genericComponentType.getTypeName() + "[]";
+		}
+	}
+}
diff --git a/src/test/java/com/fasterxml/classmate/TestResolvedTypeMapper.java b/src/test/java/com/fasterxml/classmate/TestResolvedTypeMapper.java
new file mode 100644
index 0000000..f1ebda8
--- /dev/null
+++ b/src/test/java/com/fasterxml/classmate/TestResolvedTypeMapper.java
@@ -0,0 +1,267 @@
+package com.fasterxml.classmate;
+
+import com.fasterxml.classmate.types.ResolvedArrayType;
+import com.fasterxml.classmate.types.ResolvedPrimitiveType;
+import com.fasterxml.classmate.types.ResolvedRecursiveType;
+
+import java.lang.reflect.Field;
+import java.lang.reflect.GenericArrayType;
+import java.lang.reflect.Method;
+import java.lang.reflect.ParameterizedType;
+import java.lang.reflect.Type;
+import java.util.List;
+import java.util.Map;
+import java.util.TreeMap;
+
+@SuppressWarnings("serial")
+public class TestResolvedTypeMapper extends BaseTest {
+    /*
+    /**********************************************************************
+    /* Helper types
+    /**********************************************************************
+     */
+
+	// // Multi-level resolution needed
+
+	static class MyStringLongMap extends MyStringKeyMap<Long> {
+		public Map<String, Long> expectedType;
+	}
+
+	static class MyStringKeyMap<V> extends TreeMap<String, V> {
+	}
+
+	// // For verifying "jdk type" resolution
+
+	static class ListWrapper<T> {
+		public List<T> wrap() {
+			return null;
+		}
+	}
+
+	// Since using the regular java API we cannot get a parameterized type for List<String>, add the expected type to compare the returntype of the wrap method against
+	static class StringListWrapper extends ListWrapper<String> {
+		public long field;
+
+		public List<String> expectedType;
+	}
+
+	// and recursive types...
+	static abstract class SelfRefType implements Comparable<SelfRefType> {
+	}
+
+	// And arrays (ResolvedType resolves TypeVariables to the upperbound, in this case Object[] and List<Object>[])
+	static abstract class GenericArray<E, T extends List<E>> {
+		public E[] field;
+		public Object[] expectedTypeForField;
+		public T[] boundedField;
+		public List<Object>[] expectedTypeForBoundedField;
+		public List<? super E>[] wildcardAndSuperField;
+	}
+
+	// When using concrete types, we can resolve stricter bounds for the fields in the superclass
+	static class StringArray extends GenericArray<String, List<String>> {
+		public String[] expectedType;
+		public List<String>[] expectedBoundedType;
+		public List<Object>[] expectedWildcardSuperBoundedType;
+	}
+
+	static class StringMapArray {
+		public Map<String, Long>[] field;
+	}
+    
+    /*
+    /**********************************************************************
+    /* setup
+    /**********************************************************************
+     */
+
+	// Let's use a single instance for all tests, to increase chance of seeing failures
+	protected final ResolvedTypeMapper mapper = new ResolvedTypeMapper();
+
+	// Let's use the type resolver to construct the ResolvedType used in the tests
+	protected final TypeResolver resolver = new TypeResolver();
+
+    /*
+    /**********************************************************************
+    /* Unit tests, normal operation
+    /**********************************************************************
+     */
+
+	public void testMapWithRawType() {
+		ResolvedType resolvedType = resolver.resolve(List.class);
+		assertEquals(List.class, mapper.map(resolvedType));
+	}
+
+	public void testPrimitiveTypes() {
+		for (ResolvedPrimitiveType primitiveType : ResolvedPrimitiveType.all()) {
+			assertEquals(primitiveType._erasedType, mapper.map(primitiveType));
+		}
+	}
+
+	public void testPrimitiveArrayTypes() {
+		ResolvedType resolvedType = resolver.resolve(int[].class);
+		assertEquals(int[].class, mapper.map(resolvedType));
+	}
+
+	public void testGenericUnboundedArrayTypes() throws NoSuchFieldException {
+		Field f = GenericArray.class.getDeclaredField("field");
+		ResolvedType genericArrayType = resolver.resolve(GenericArray.class);
+		ResolvedType fieldType = resolver.resolve(genericArrayType.getTypeBindings(), f.getGenericType());
+		Type mappedArrayType = mapper.map(fieldType);
+		// Check it is a Object[]
+		assertEquals(GenericArray.class.getDeclaredField("expectedTypeForField").getGenericType(), mappedArrayType);
+		assertTrue(mappedArrayType instanceof Class<?>);
+	}
+
+	public void testGenericBoundedArrayTypes() throws NoSuchFieldException {
+		Field f = GenericArray.class.getDeclaredField("boundedField");
+		ResolvedType genericArrayType = resolver.resolve(GenericArray.class);
+		ResolvedType fieldType = resolver.resolve(genericArrayType.getTypeBindings(), f.getGenericType());
+		Type mappedArrayType = mapper.map(fieldType);
+		// Check it is a List<Object>[]
+		Type expectedGenericType = GenericArray.class.getDeclaredField("expectedTypeForBoundedField").getGenericType();
+		assertEquals(expectedGenericType, mappedArrayType);
+		assertTrue(mappedArrayType instanceof GenericArrayType);
+		//Test equals is symmetric
+		assertEquals(mappedArrayType, expectedGenericType);
+	}
+
+	public void testGenericWildcardWithSuperArrayTypes() throws NoSuchFieldException {
+		Field f = GenericArray.class.getDeclaredField("wildcardAndSuperField");
+		ResolvedType genericArrayType = resolver.resolve(GenericArray.class);
+		ResolvedType fieldType = resolver.resolve(genericArrayType.getTypeBindings(), f.getGenericType());
+		Type mappedArrayType = mapper.map(fieldType);
+		// Check it is a List<Object>[]
+		assertEquals(GenericArray.class.getDeclaredField("expectedTypeForBoundedField").getGenericType(), mappedArrayType);
+		assertTrue(mappedArrayType instanceof GenericArrayType);
+
+		// Even after resolving E, we would still get the same upper bound, since we are using super
+		ResolvedType stringArrayType = resolver.resolve(StringArray.class);
+		assertEquals(StringArray.class, mapper.map(stringArrayType));
+		ResolvedType resolvedType = resolver.resolve(stringArrayType.getParentClass().getTypeBindings(), f.getGenericType());
+		// Check it is a List<Object>[]
+		assertEquals(StringArray.class.getDeclaredField("expectedWildcardSuperBoundedType").getGenericType(), mapper.map(resolvedType));
+	}
+
+	public void testConcreteArrayTypes() throws NoSuchFieldException {
+		Field f = GenericArray.class.getDeclaredField("field");
+		ResolvedType stringArrayType = resolver.resolve(StringArray.class);
+		assertEquals(StringArray.class, mapper.map(stringArrayType));
+
+		ResolvedType resolvedType = resolver.resolve(stringArrayType.getParentClass().getTypeBindings(), f.getGenericType());
+		Type mappedArrayType = mapper.map(resolvedType);
+		// Check it is a String[]
+		assertEquals(StringArray.class.getDeclaredField("expectedType").getGenericType(), mappedArrayType);
+		assertTrue(mappedArrayType instanceof Class<?>);
+	}
+
+	public void testConcreteParameterArrayTypes() throws NoSuchFieldException {
+		Field f = GenericArray.class.getDeclaredField("boundedField");
+		ResolvedType stringArrayType = resolver.resolve(StringArray.class);
+		assertEquals(StringArray.class, mapper.map(stringArrayType));
+
+		ResolvedType resolvedType = resolver.resolve(stringArrayType.getParentClass().getTypeBindings(), f.getGenericType());
+		Type mappedArrayType = mapper.map(resolvedType);
+		// Check it is a List<String>[]
+		assertEquals(StringArray.class.getDeclaredField("expectedBoundedType").getGenericType(), mappedArrayType);
+		assertTrue(mappedArrayType instanceof GenericArrayType);
+	}
+
+	public void testParameterizedArrayTypes() throws NoSuchFieldException {
+		Field f = StringMapArray.class.getDeclaredField("field");
+		ResolvedType stringMapArrayType = resolver.resolve(StringMapArray.class);
+		assertEquals(StringMapArray.class, mapper.map(stringMapArrayType));
+
+		ResolvedType resolvedType = resolver.resolve(stringMapArrayType.getTypeBindings(), f.getGenericType());
+		// Check it is a Map<String, Long>[]
+		Type mappedArrayType = mapper.map(resolvedType);
+		assertEquals(f.getGenericType(), mappedArrayType);
+		assertTrue(mappedArrayType instanceof GenericArrayType);
+
+	}
+
+	public void testGenericMap() {
+		// First, direct ref
+		GenericType<?> mapInput = new GenericType<Map<String, Long>>() {
+		};
+		ResolvedType mapType = resolver.resolve(mapInput);
+
+		//Parameterized map type, since GenericType is skipped
+		ParameterizedType parameterizedMapType = (ParameterizedType) ((ParameterizedType) mapInput.getClass().getGenericSuperclass()).getActualTypeArguments()[0];
+		assertEquals(parameterizedMapType, mapper.map(mapType));
+		// Test equals is symmetric for ParameterizedType
+		assertEquals(mapper.map(mapType), parameterizedMapType);
+
+		//String
+		Type mappedString = mapper.map(mapType.getTypeParameters().get(0));
+		assertEquals(parameterizedMapType.getActualTypeArguments()[0], mappedString);
+		assertEquals(String.class, mappedString);
+		//Long
+		Type mappedLong = mapper.map(mapType.getTypeParameters().get(1));
+		assertEquals(parameterizedMapType.getActualTypeArguments()[1], mappedLong);
+		assertEquals(Long.class, mappedLong);
+	}
+
+	public void testParametricMap() throws NoSuchFieldException {
+		ResolvedType mapType = resolver.resolve(MyStringLongMap.class);
+
+		assertEquals(MyStringLongMap.class,  mapper.map(mapType));
+		// Ensure we can find parameters for Map
+		ResolvedType mapSuperType = mapType.findSupertype(Map.class);
+		// Check if it is a Map<String, Long>
+		assertEquals(MyStringLongMap.class.getDeclaredField("expectedType").getGenericType(), mapper.map(mapSuperType));
+	}
+
+	public void testJdkType() throws Exception {
+		ResolvedType wrapperType = resolver.resolve(StringListWrapper.class);
+		Field f = StringListWrapper.class.getDeclaredField("field");
+		// first; field has no generic stuff, should be simple
+		ResolvedType fieldType = resolver.resolve(wrapperType.getTypeBindings(), f.getGenericType());
+		assertEquals(Long.TYPE, mapper.map(fieldType));
+
+		// but method return type is templatized; and MUST be given correct type bindings!
+		Method m = ListWrapper.class.getDeclaredMethod("wrap");
+		ResolvedType superType = wrapperType.getParentClass();
+		ResolvedType methodReturnType = resolver.resolve(superType.getTypeBindings(),
+				m.getGenericReturnType());
+		// should be List<String>, but we cannot access that from the method, so we compare it to a typed field from the java API
+		Type expectedType = StringListWrapper.class.getField("expectedType").getGenericType();
+		assertEquals(expectedType, mapper.map(methodReturnType));
+	}
+
+	public void testSimpleSelfRef() {
+		ResolvedType type = resolver.resolve(SelfRefType.class);
+		List<ResolvedType> interfaces = type.getImplementedInterfaces();
+		assertEquals(1, interfaces.size());
+		ResolvedType compType = interfaces.get(0);
+		assertEquals(SelfRefType.class.getGenericInterfaces()[0], mapper.map(compType));
+	}
+
+	/*
+    /**********************************************************************
+    /* Unit tests, error cases
+    /**********************************************************************
+     */
+
+	public void testNullabilityInResolvedRecursiveType() {
+		ResolvedRecursiveType resolvedType = new ResolvedRecursiveType(Integer.class, TypeBindings.emptyBindings());
+		//empty reference
+		try {
+			mapper.map(resolvedType);
+			fail("Expected failure");
+		} catch (IllegalStateException e) {
+			verifyException(e, "Missing self referenced type");
+		}
+	}
+
+	public void testNullabilityInResolvedArrayType() {
+		ResolvedArrayType resolvedType = new ResolvedArrayType(Integer.class, TypeBindings.emptyBindings(), null);
+		//empty reference
+		try {
+			mapper.map(resolvedType);
+			fail("Expected failure");
+		} catch (IllegalStateException e) {
+			verifyException(e, "Missing array element type");
+		}
+	}
+}