Use non-lenient constructor resolution mode for @Bean methods

Since @Bean methods are never used with externally specified constructor argument values but rather just with autowiring, the non-lenient constructor resolution mode is appropriate in case of an overloaded @Bean method, not performing any type difference weight checks. This change includes a refinement of Spring's existing non-lenient constructor resolution (which needs to be explicitly turned on and is therefore not well tested), narrowing the conditions for the ambiguity check (only in case of the same number of arguments and not for overridden methods).

Issue: SPR-10988

spring-beans/src/main/java/org/springframework/beans/factory/support/ConstructorResolver.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.
@@ -151,7 +151,7 @@ class ConstructorResolver {
 			// Take specified constructors, if any.
 			Constructor[] candidates = chosenCtors;
 			if (candidates == null) {
-				Class beanClass = mbd.getBeanClass();
+				Class<?> beanClass = mbd.getBeanClass();
 				try {
 					candidates = (mbd.isNonPublicAccessAllowed() ?
 							beanClass.getDeclaredConstructors() : beanClass.getConstructors());
@@ -169,7 +169,7 @@ class ConstructorResolver {
 
 			for (int i = 0; i < candidates.length; i++) {
 				Constructor<?> candidate = candidates[i];
-				Class[] paramTypes = candidate.getParameterTypes();
+				Class<?>[] paramTypes = candidate.getParameterTypes();
 
 				if (constructorToUse != null && argsToUse.length > paramTypes.length) {
 					// Already found greedy constructor that can be satisfied ->
@@ -342,7 +342,7 @@ class ConstructorResolver {
 		this.beanFactory.initBeanWrapper(bw);
 
 		Object factoryBean;
-		Class factoryClass;
+		Class<?> factoryClass;
 		boolean isStatic;
 
 		String factoryBeanName = mbd.getFactoryBeanName();
@@ -400,7 +400,7 @@ class ConstructorResolver {
 			factoryClass = ClassUtils.getUserClass(factoryClass);
 			Method[] rawCandidates;
 
-			final Class factoryClazz = factoryClass;
+			final Class<?> factoryClazz = factoryClass;
 			if (System.getSecurityManager() != null) {
 				rawCandidates = AccessController.doPrivileged(new PrivilegedAction<Method[]>() {
 					@Override
@@ -447,7 +447,7 @@ class ConstructorResolver {
 
 			for (int i = 0; i < candidates.length; i++) {
 				Method candidate = candidates[i];
-				Class[] paramTypes = candidate.getParameterTypes();
+				Class<?>[] paramTypes = candidate.getParameterTypes();
 
 				if (paramTypes.length >= minNrOfArgs) {
 					ArgumentsHolder argsHolder;
@@ -505,7 +505,15 @@ class ConstructorResolver {
 						minTypeDiffWeight = typeDiffWeight;
 						ambiguousFactoryMethods = null;
 					}
-					else if (factoryMethodToUse != null && typeDiffWeight == minTypeDiffWeight) {
+					// Find out about ambiguity: In case of the same type difference weight
+					// for methods with the same number of parameters, collect such candidates
+					// and eventually raise an ambiguity exception.
+					// However, only perform that check in non-lenient constructor resolution mode,
+					// and explicitly ignore overridden methods (with the same parameter signature).
+					else if (factoryMethodToUse != null && typeDiffWeight == minTypeDiffWeight &&
+							!mbd.isLenientConstructorResolution() &&
+							paramTypes.length == factoryMethodToUse.getParameterTypes().length &&
+							!Arrays.equals(paramTypes, factoryMethodToUse.getParameterTypes())) {
 						if (ambiguousFactoryMethods == null) {
 							ambiguousFactoryMethods = new LinkedHashSet<Method>();
 							ambiguousFactoryMethods.add(factoryMethodToUse);
@@ -542,7 +550,7 @@ class ConstructorResolver {
 						"Invalid factory method '" + mbd.getFactoryMethodName() +
 						"': needs to have a non-void return type!");
 			}
-			else if (ambiguousFactoryMethods != null && !mbd.isLenientConstructorResolution()) {
+			else if (ambiguousFactoryMethods != null) {
 				throw new BeanCreationException(mbd.getResourceDescription(), beanName,
 						"Ambiguous factory method matches found in bean '" + beanName + "' " +
 						"(hint: specify index/type/name arguments for simple parameters to avoid type ambiguities): " +
@@ -647,7 +655,7 @@ class ConstructorResolver {
 	 */
 	private ArgumentsHolder createArgumentArray(
 			String beanName, RootBeanDefinition mbd, ConstructorArgumentValues resolvedValues,
-			BeanWrapper bw, Class[] paramTypes, String[] paramNames, Object methodOrCtor,
+			BeanWrapper bw, Class<?>[] paramTypes, String[] paramNames, Object methodOrCtor,
 			boolean autowiring) throws UnsatisfiedDependencyException {
 
 		String methodType = (methodOrCtor instanceof Constructor ? "constructor" : "factory method");
@@ -753,7 +761,7 @@ class ConstructorResolver {
 	private Object[] resolvePreparedArguments(
 			String beanName, RootBeanDefinition mbd, BeanWrapper bw, Member methodOrCtor, Object[] argsToResolve) {
 
-		Class[] paramTypes = (methodOrCtor instanceof Method ?
+		Class<?>[] paramTypes = (methodOrCtor instanceof Method ?
 				((Method) methodOrCtor).getParameterTypes() : ((Constructor) methodOrCtor).getParameterTypes());
 		TypeConverter converter = (this.beanFactory.getCustomTypeConverter() != null ?
 				this.beanFactory.getCustomTypeConverter() : bw);
@@ -825,7 +833,7 @@ class ConstructorResolver {
 			this.preparedArguments = args;
 		}
 
-		public int getTypeDifferenceWeight(Class[] paramTypes) {
+		public int getTypeDifferenceWeight(Class<?>[] paramTypes) {
 			// If valid arguments found, determine type difference weight.
 			// Try type difference weight on both the converted arguments and
 			// the raw arguments. If the raw weight is better, use it.
@@ -835,7 +843,7 @@ class ConstructorResolver {
 			return (rawTypeDiffWeight < typeDiffWeight ? rawTypeDiffWeight : typeDiffWeight);
 		}
 
-		public int getAssignabilityWeight(Class[] paramTypes) {
+		public int getAssignabilityWeight(Class<?>[] paramTypes) {
 			for (int i = 0; i < paramTypes.length; i++) {
 				if (!ClassUtils.isAssignableValue(paramTypes[i], this.arguments[i])) {
 					return Integer.MAX_VALUE;

spring-context/src/main/java/org/springframework/context/annotation/ConfigurationClassBeanDefinitionReader.java

@@ -332,6 +332,7 @@ class ConfigurationClassBeanDefinitionReader {
 
 		public ConfigurationClassBeanDefinition(ConfigurationClass configClass) {
 			this.annotationMetadata = configClass.getMetadata();
+			setLenientConstructorResolution(false);
 		}
 
 		public ConfigurationClassBeanDefinition(RootBeanDefinition original, ConfigurationClass configClass) {

spring-context/src/test/java/org/springframework/context/annotation/BeanMethodPolymorphismTests.java

@@ -19,10 +19,10 @@ package org.springframework.context.annotation;
 import java.lang.annotation.Inherited;
 import java.util.List;
 
-import org.junit.Ignore;
 import org.junit.Rule;
 import org.junit.Test;
 import org.junit.rules.ExpectedException;
+
 import org.springframework.beans.factory.parsing.BeanDefinitionParsingException;
 import org.springframework.beans.factory.support.DefaultListableBeanFactory;
 import org.springframework.beans.factory.support.RootBeanDefinition;
@@ -74,7 +74,6 @@ public class BeanMethodPolymorphismTests {
 	}
 
 	@Test
-	@Ignore
 	public void beanMethodOverloadingWithInheritanceAndList() {
 		// SPR-11025
 		AnnotationConfigApplicationContext ctx = new AnnotationConfigApplicationContext(SubConfigWithList.class);

spring-core/src/main/java/org/springframework/util/MethodInvoker.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.
@@ -40,7 +40,7 @@ import java.lang.reflect.Modifier;
  */
 public class MethodInvoker {
 
-	private Class targetClass;
+	private Class<?> targetClass;
 
 	private Object targetObject;
 
@@ -61,14 +61,14 @@ public class MethodInvoker {
 	 * @see #setTargetObject
 	 * @see #setTargetMethod
 	 */
-	public void setTargetClass(Class targetClass) {
+	public void setTargetClass(Class<?> targetClass) {
 		this.targetClass = targetClass;
 	}
 
 	/**
 	 * Return the target class on which to call the target method.
 	 */
-	public Class getTargetClass() {
+	public Class<?> getTargetClass() {
 		return this.targetClass;
 	}
 
@@ -158,7 +158,7 @@ public class MethodInvoker {
 			this.targetMethod = methodName;
 		}
 
-		Class targetClass = getTargetClass();
+		Class<?> targetClass = getTargetClass();
 		String targetMethod = getTargetMethod();
 		if (targetClass == null) {
 			throw new IllegalArgumentException("Either 'targetClass' or 'targetObject' is required");
@@ -194,7 +194,7 @@ public class MethodInvoker {
 	 * @return the resolved Class
 	 * @throws ClassNotFoundException if the class name was invalid
 	 */
-	protected Class resolveClassName(String className) throws ClassNotFoundException {
+	protected Class<?> resolveClassName(String className) throws ClassNotFoundException {
 		return ClassUtils.forName(className, ClassUtils.getDefaultClassLoader());
 	}
 
@@ -287,19 +287,22 @@ public class MethodInvoker {
 	 * Therefore, with an arg of type Integer, a constructor (Integer) would be preferred to a
 	 * constructor (Number) which would in turn be preferred to a constructor (Object).
 	 * All argument weights get accumulated.
+	 * <p>Note: This is the algorithm used by MethodInvoker itself and also the algorithm
+	 * used for constructor and factory method selection in Spring's bean container (in case
+	 * of lenient constructor resolution which is the default for regular bean definitions).
 	 * @param paramTypes the parameter types to match
 	 * @param args the arguments to match
 	 * @return the accumulated weight for all arguments
 	 */
-	public static int getTypeDifferenceWeight(Class[] paramTypes, Object[] args) {
+	public static int getTypeDifferenceWeight(Class<?>[] paramTypes, Object[] args) {
 		int result = 0;
 		for (int i = 0; i < paramTypes.length; i++) {
 			if (!ClassUtils.isAssignableValue(paramTypes[i], args[i])) {
 				return Integer.MAX_VALUE;
 			}
 			if (args[i] != null) {
-				Class paramType = paramTypes[i];
+				Class<?> paramType = paramTypes[i];
-				Class superClass = args[i].getClass().getSuperclass();
+				Class<?> superClass = args[i].getClass().getSuperclass();
 				while (superClass != null) {
 					if (paramType.equals(superClass)) {
 						result = result + 2;