Generic bean type resolution for lookup methods

Closes gh-26998

spring-beans/src/main/java/org/springframework/beans/factory/support/CglibSubclassingInstantiationStrategy.java

 /*
- * Copyright 2002-2020 the original author or authors.
+ * Copyright 2002-2021 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.
@@ -35,6 +35,7 @@ import org.springframework.cglib.proxy.Factory;
 import org.springframework.cglib.proxy.MethodInterceptor;
 import org.springframework.cglib.proxy.MethodProxy;
 import org.springframework.cglib.proxy.NoOp;
+import org.springframework.core.ResolvableType;
 import org.springframework.lang.Nullable;
 import org.springframework.util.Assert;
 import org.springframework.util.StringUtils;
@@ -244,8 +245,10 @@ public class CglibSubclassingInstantiationStrategy extends SimpleInstantiationSt
 				return (bean.equals(null) ? null : bean);
 			}
 			else {
-				return (argsToUse != null ? this.owner.getBean(method.getReturnType(), argsToUse) :
-						this.owner.getBean(method.getReturnType()));
+				// Find target bean matching the (potentially generic) method return type
+				ResolvableType genericReturnType = ResolvableType.forMethodReturnType(method);
+				return (argsToUse != null ? this.owner.getBeanProvider(genericReturnType).getObject(argsToUse) :
+						this.owner.getBeanProvider(genericReturnType).getObject());
 			}
 		}
 	}

spring-beans/src/main/java/org/springframework/beans/factory/support/LookupOverride.java

 /*
- * Copyright 2002-2017 the original author or authors.
+ * Copyright 2002-2021 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.
@@ -19,17 +19,25 @@ package org.springframework.beans.factory.support;
 import java.lang.reflect.Method;
 import java.lang.reflect.Modifier;
 
+import org.springframework.core.ResolvableType;
 import org.springframework.lang.Nullable;
 import org.springframework.util.ObjectUtils;
 
 /**
- * Represents an override of a method that looks up an object in the same IoC context.
+ * Represents an override of a method that looks up an object in the same IoC context,
+ * either by bean name or by bean type (based on the declared method return type).
  *
- * <p>Methods eligible for lookup override must not have arguments.
+ * <p>Methods eligible for lookup override may declare arguments in which case the
+ * given arguments are passed to the bean retrieval operation.
  *
  * @author Rod Johnson
  * @author Juergen Hoeller
  * @since 1.1
+ * @see org.springframework.beans.factory.BeanFactory#getBean(String)
+ * @see org.springframework.beans.factory.BeanFactory#getBean(Class)
+ * @see org.springframework.beans.factory.BeanFactory#getBean(String, Object...)
+ * @see org.springframework.beans.factory.BeanFactory#getBean(Class, Object...)
+ * @see org.springframework.beans.factory.BeanFactory#getBeanProvider(ResolvableType)
  */
 public class LookupOverride extends MethodOverride {
 
@@ -43,8 +51,8 @@ public class LookupOverride extends MethodOverride {
 	/**
 	 * Construct a new LookupOverride.
 	 * @param methodName the name of the method to override
-	 * @param beanName the name of the bean in the current {@code BeanFactory}
-	 * that the overridden method should return (may be {@code null})
+	 * @param beanName the name of the bean in the current {@code BeanFactory} that the
+	 * overridden method should return (may be {@code null} for type-based bean retrieval)
 	 */
 	public LookupOverride(String methodName, @Nullable String beanName) {
 		super(methodName);
@@ -53,9 +61,9 @@ public class LookupOverride extends MethodOverride {
 
 	/**
 	 * Construct a new LookupOverride.
-	 * @param method the method to override
-	 * @param beanName the name of the bean in the current {@code BeanFactory}
-	 * that the overridden method should return (may be {@code null})
+	 * @param method the method declaration to override
+	 * @param beanName the name of the bean in the current {@code BeanFactory} that the
+	 * overridden method should return (may be {@code null} for type-based bean retrieval)
 	 */
 	public LookupOverride(Method method, @Nullable String beanName) {
 		super(method.getName());

spring-beans/src/main/java/org/springframework/beans/factory/support/MethodReplacer.java

 /*
- * Copyright 2002-2012 the original author or authors.
+ * Copyright 2002-2021 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.
@@ -19,9 +19,8 @@ package org.springframework.beans.factory.support;
 import java.lang.reflect.Method;
 
 /**
- * Interface to be implemented by classes that can reimplement any method
- * on an IoC-managed object: the <b>Method Injection</b> form of
- * Dependency Injection.
+ * Interface to be implemented by classes that can reimplement any method on an
+ * IoC-managed object: the <b>Method Injection</b> form of Dependency Injection.
  *
  * <p>Such methods may be (but need not be) abstract, in which case the
  * container will create a concrete subclass to instantiate.

spring-beans/src/main/java/org/springframework/beans/factory/support/ReplaceOverride.java

 /*
- * Copyright 2002-2020 the original author or authors.
+ * Copyright 2002-2021 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.
@@ -25,7 +25,7 @@ import org.springframework.util.Assert;
 import org.springframework.util.ObjectUtils;
 
 /**
- * Extension of MethodOverride that represents an arbitrary
+ * Extension of {@link MethodOverride} that represents an arbitrary
  * override of a method by the IoC container.
  *
  * <p>Any non-final method can be overridden, irrespective of its
@@ -45,7 +45,7 @@ public class ReplaceOverride extends MethodOverride {
 	/**
 	 * Construct a new ReplaceOverride.
 	 * @param methodName the name of the method to override
-	 * @param methodReplacerBeanName the bean name of the MethodReplacer
+	 * @param methodReplacerBeanName the bean name of the {@link MethodReplacer}
 	 */
 	public ReplaceOverride(String methodName, String methodReplacerBeanName) {
 		super(methodName);

spring-beans/src/test/java/org/springframework/beans/factory/annotation/LookupAnnotationTests.java

 /*
- * Copyright 2002-2020 the original author or authors.
+ * Copyright 2002-2021 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.
@@ -121,6 +121,18 @@ public class LookupAnnotationTests {
 		assertThat(beanFactory.getBean(BeanConsumer.class).abstractBean).isSameAs(bean);
 	}
 
+	@Test
+	public void testWithGenericBean() {
+		beanFactory.registerBeanDefinition("numberBean", new RootBeanDefinition(NumberBean.class));
+		beanFactory.registerBeanDefinition("doubleStore", new RootBeanDefinition(DoubleStore.class));
+		beanFactory.registerBeanDefinition("floatStore", new RootBeanDefinition(FloatStore.class));
+
+		NumberBean bean = (NumberBean) beanFactory.getBean("numberBean");
+		assertThat(bean).isNotNull();
+		assertThat(beanFactory.getBean(DoubleStore.class)).isSameAs(bean.getDoubleStore());
+		assertThat(beanFactory.getBean(FloatStore.class)).isSameAs(bean.getFloatStore());
+	}
+
 
 	public static abstract class AbstractBean {
 
@@ -147,4 +159,26 @@ public class LookupAnnotationTests {
 		AbstractBean abstractBean;
 	}
 
+
+	public static class NumberStore<T extends Number> {
+	}
+
+
+	public static class DoubleStore extends NumberStore<Double> {
+	}
+
+
+	public static class FloatStore extends NumberStore<Float> {
+	}
+
+
+	public static abstract class NumberBean {
+
+		@Lookup
+		public abstract NumberStore<Double> getDoubleStore();
+
+		@Lookup
+		public abstract NumberStore<Float> getFloatStore();
+	}
+
 }

spring-beans/src/test/java/org/springframework/beans/factory/support/LookupMethodTests.java

 /*
- * Copyright 2002-2019 the original author or authors.
+ * Copyright 2002-2021 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.
@@ -36,7 +36,7 @@ public class LookupMethodTests {
 
 
 	@BeforeEach
-	public void setUp() {
+	public void setup() {
 		beanFactory = new DefaultListableBeanFactory();
 		XmlBeanDefinitionReader reader = new XmlBeanDefinitionReader(beanFactory);
 		reader.loadBeanDefinitions(new ClassPathResource("lookupMethodTests.xml", getClass()));
@@ -83,8 +83,8 @@ public class LookupMethodTests {
 	public void testWithThreeArgsShouldFail() {
 		AbstractBean bean = (AbstractBean) beanFactory.getBean("abstractBean");
 		assertThat(bean).isNotNull();
-		assertThatExceptionOfType(AbstractMethodError.class).as("does not have a three arg constructor").isThrownBy(() ->
-			bean.getThreeArguments("name", 1, 2));
+		assertThatExceptionOfType(AbstractMethodError.class).as("does not have a three arg constructor")
+				.isThrownBy(() -> bean.getThreeArguments("name", 1, 2));
 	}
 
 	@Test
@@ -97,6 +97,21 @@ public class LookupMethodTests {
 		assertThat(expected.isJedi()).isTrue();
 	}
 
+	@Test
+	public void testWithGenericBean() {
+		RootBeanDefinition bd = new RootBeanDefinition(NumberBean.class);
+		bd.getMethodOverrides().addOverride(new LookupOverride("getDoubleStore", null));
+		bd.getMethodOverrides().addOverride(new LookupOverride("getFloatStore", null));
+		beanFactory.registerBeanDefinition("numberBean", bd);
+		beanFactory.registerBeanDefinition("doubleStore", new RootBeanDefinition(DoubleStore.class));
+		beanFactory.registerBeanDefinition("floatStore", new RootBeanDefinition(FloatStore.class));
+
+		NumberBean bean = (NumberBean) beanFactory.getBean("numberBean");
+		assertThat(bean).isNotNull();
+		assertThat(beanFactory.getBean(DoubleStore.class)).isSameAs(bean.getDoubleStore());
+		assertThat(beanFactory.getBean(FloatStore.class)).isSameAs(bean.getFloatStore());
+	}
+
 
 	public static abstract class AbstractBean {
 
@@ -111,4 +126,24 @@ public class LookupMethodTests {
 		public abstract TestBean getThreeArguments(String name, int age, int anotherArg);
 	}
 
+
+	public static class NumberStore<T extends Number> {
+	}
+
+
+	public static class DoubleStore extends NumberStore<Double> {
+	}
+
+
+	public static class FloatStore extends NumberStore<Float> {
+	}
+
+
+	public static abstract class NumberBean {
+
+		public abstract NumberStore<Double> getDoubleStore();
+
+		public abstract NumberStore<Float> getFloatStore();
+	}
+
 }