Workaround for inner class constructor parameter annotation bug in javac

Issue: SPR-16652

Author: jhoeller

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

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2017 the original author or authors.
+ * Copyright 2002-2018 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.
@@ -22,6 +22,7 @@
 import java.lang.reflect.Executable;
 import java.lang.reflect.Member;
 import java.lang.reflect.Method;
+import java.lang.reflect.Modifier;
 import java.lang.reflect.Parameter;
 import java.lang.reflect.ParameterizedType;
 import java.lang.reflect.Type;
@@ -57,6 +58,8 @@
  */
 public class MethodParameter {
 
+	private static final Annotation[] EMPTY_ANNOTATION_ARRAY = new Annotation[0];
+
 	private final Executable executable;
 
 	private final int parameterIndex;
@@ -514,11 +517,20 @@ public Annotation[] getParameterAnnotations() {
 		Annotation[] paramAnns = this.parameterAnnotations;
 		if (paramAnns == null) {
 			Annotation[][] annotationArray = this.executable.getParameterAnnotations();
-			if (this.parameterIndex >= 0 && this.parameterIndex < annotationArray.length) {
-				paramAnns = adaptAnnotationArray(annotationArray[this.parameterIndex]);
+			int index = this.parameterIndex;
+			if (this.executable instanceof Constructor &&
+					this.executable.getDeclaringClass().isMemberClass() &&
+					!Modifier.isStatic(this.executable.getDeclaringClass().getModifiers()) &&
+					annotationArray.length == this.executable.getParameterCount() - 1) {
+				// Bug in javac in JDK <9: annotation array excludes enclosing instance parameter
+				// 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 = new Annotation[0];
+				paramAnns = EMPTY_ANNOTATION_ARRAY;
 			}
 			this.parameterAnnotations = paramAnns;
 		}

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

@@ -24,7 +24,6 @@
 import java.lang.reflect.Method;
 
 import org.junit.Before;
-import org.junit.Ignore;
 import org.junit.Test;
 
 import static org.junit.Assert.*;
@@ -46,7 +45,7 @@ public class MethodParameterTests {
 
 
 	@Before
-	public void setUp() throws NoSuchMethodException {
+	public void setup() throws NoSuchMethodException {
 		method = getClass().getMethod("method", String.class, Long.TYPE);
 		stringParameter = new MethodParameter(method, 0);
 		longParameter = new MethodParameter(method, 1);
@@ -114,15 +113,22 @@ public void annotatedConstructorParameterInStaticNestedClass() throws Exception
 		assertNotNull(methodParameter.getParameterAnnotation(Param.class));
 	}
 
-	@Test
-	@Ignore("Disabled until SPR-16652 is resolved")
+	@Test  // SPR-16652
 	public void annotatedConstructorParameterInInnerClass() throws Exception {
-		Constructor<?> constructor = InnerClass.class.getDeclaredConstructor(getClass(), String.class);
-		MethodParameter methodParameter = MethodParameter.forExecutable(constructor, 1);
+		Constructor<?> constructor = InnerClass.class.getConstructor(getClass(), String.class, Integer.class);
+
+		MethodParameter methodParameter = MethodParameter.forExecutable(constructor, 0);
+		assertEquals(getClass(), methodParameter.getParameterType());
+		assertNull(methodParameter.getParameterAnnotation(Param.class));
+
+		methodParameter = MethodParameter.forExecutable(constructor, 1);
 		assertEquals(String.class, methodParameter.getParameterType());
-		assertNull(methodParameter.getParameterAnnotation(Override.class));
 		// The following assertion currently fails if this test class is compiled using JDK 8.
 		assertNotNull("Failed to find @Param annotation", methodParameter.getParameterAnnotation(Param.class));
+
+		methodParameter = MethodParameter.forExecutable(constructor, 2);
+		assertEquals(Integer.class, methodParameter.getParameterType());
+		assertNull(methodParameter.getParameterAnnotation(Param.class));
 	}
 
 
@@ -140,7 +146,7 @@ private static class NestedClass {
 	@SuppressWarnings("unused")
 	private class InnerClass {
 
-		InnerClass(@Param String s) {
+		public InnerClass(@Param String s, Integer i) {
 		}
 	}