Workaround for generic parameter types on inner class constructors

Issue: SPR-16734

spring-core/src/main/java/org/springframework/core/MethodParameter.java

@@ -419,7 +419,18 @@ public class MethodParameter {
 				paramType = (method != null ? method.getGenericReturnType() : void.class);
 			}
 			else {
-				paramType = this.executable.getGenericParameterTypes()[this.parameterIndex];
+				Type[] genericParameterTypes = this.executable.getGenericParameterTypes();
+				int index = this.parameterIndex;
+				if (this.executable instanceof Constructor &&
+						ClassUtils.isInnerClass(this.executable.getDeclaringClass()) &&
+						genericParameterTypes.length == this.executable.getParameterCount() - 1) {
+					// Bug in javac: type array excludes enclosing instance parameter
+					// for inner classes with at least one generic constructor parameter,
+					// so access it with the actual parameter index lowered by 1
+					index = this.parameterIndex - 1;
+				}
+				paramType = (index >= 0 && index < genericParameterTypes.length ?
+						genericParameterTypes[index] : getParameterType());
 			}
 			this.genericParameterType = paramType;
 		}
@@ -525,12 +536,8 @@ public class MethodParameter {
 				// for inner classes, so access it with the actual parameter index lowered by 1
 				index = this.parameterIndex - 1;
 			}
-			if (index >= 0 && index < annotationArray.length) {
-				paramAnns = adaptAnnotationArray(annotationArray[index]);
-			}
-			else {
-				paramAnns = EMPTY_ANNOTATION_ARRAY;
-			}
+			paramAnns = (index >= 0 && index < annotationArray.length ?
+					adaptAnnotationArray(annotationArray[index]) : EMPTY_ANNOTATION_ARRAY);
 			this.parameterAnnotations = paramAnns;
 		}
 		return paramAnns;
@@ -770,7 +777,6 @@ public class MethodParameter {
 			}
 			return false;
 		}
-		
 	}
 
 }

spring-core/src/test/java/org/springframework/core/MethodParameterTests.java

@@ -22,6 +22,7 @@ import java.lang.annotation.RetentionPolicy;
 import java.lang.annotation.Target;
 import java.lang.reflect.Constructor;
 import java.lang.reflect.Method;
+import java.util.concurrent.Callable;
 
 import org.junit.Before;
 import org.junit.Test;
@@ -114,7 +115,7 @@ public class MethodParameterTests {
 
 	@Test  // SPR-16652
 	public void annotatedConstructorParameterInInnerClass() throws Exception {
-		Constructor<?> constructor = InnerClass.class.getConstructor(getClass(), String.class, Integer.class);
+		Constructor<?> constructor = InnerClass.class.getConstructor(getClass(), String.class, Callable.class);
 
 		MethodParameter methodParameter = MethodParameter.forExecutable(constructor, 0);
 		assertEquals(getClass(), methodParameter.getParameterType());
@@ -125,10 +126,28 @@ public class MethodParameterTests {
 		assertNotNull("Failed to find @Param annotation", methodParameter.getParameterAnnotation(Param.class));
 
 		methodParameter = MethodParameter.forExecutable(constructor, 2);
-		assertEquals(Integer.class, methodParameter.getParameterType());
+		assertEquals(Callable.class, methodParameter.getParameterType());
 		assertNull(methodParameter.getParameterAnnotation(Param.class));
 	}
 
+	@Test  // SPR-16734
+	public void genericConstructorParameterInInnerClass() throws Exception {
+		Constructor<?> constructor = InnerClass.class.getConstructor(getClass(), String.class, Callable.class);
+
+		MethodParameter methodParameter = MethodParameter.forExecutable(constructor, 0);
+		assertEquals(getClass(), methodParameter.getParameterType());
+		assertEquals(getClass(), methodParameter.getGenericParameterType());
+
+		methodParameter = MethodParameter.forExecutable(constructor, 1);
+		assertEquals(String.class, methodParameter.getParameterType());
+		assertEquals(String.class, methodParameter.getGenericParameterType());
+
+		methodParameter = MethodParameter.forExecutable(constructor, 2);
+		assertEquals(Callable.class, methodParameter.getParameterType());
+		assertEquals(ResolvableType.forClassWithGenerics(Callable.class, Integer.class).getType(),
+				methodParameter.getGenericParameterType());
+	}
+
 
 	public int method(String p1, long p2) {
 		return 42;
@@ -144,7 +163,7 @@ public class MethodParameterTests {
 	@SuppressWarnings("unused")
 	private class InnerClass {
 
-		public InnerClass(@Param String s, Integer i) {
+		public InnerClass(@Param String s, Callable<Integer> i) {
 		}
 	}