Support for functional instance supplier callback at BeanDefinition level

Issue: SPR-14832

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

@@ -38,6 +38,7 @@ import java.util.Set;
 import java.util.TreeSet;
 import java.util.concurrent.ConcurrentHashMap;
 import java.util.concurrent.ConcurrentMap;
+import java.util.function.Supplier;
 
 import org.springframework.beans.BeanUtils;
 import org.springframework.beans.BeanWrapper;
@@ -1036,6 +1037,13 @@ public abstract class AbstractAutowireCapableBeanFactory extends AbstractBeanFac
 					"Bean class isn't public, and non-public access not allowed: " + beanClass.getName());
 		}
 
+		Supplier<?> instanceSupplier = mbd.getInstanceSupplier();
+		if (instanceSupplier != null) {
+			BeanWrapper bw = new BeanWrapperImpl(instanceSupplier.get());
+			initBeanWrapper(bw);
+			return bw;
+		}
+
 		if (mbd.getFactoryMethodName() != null)  {
 			return instantiateUsingFactoryMethod(beanName, mbd, args);
 		}

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

@@ -22,6 +22,7 @@ import java.util.LinkedHashMap;
 import java.util.LinkedHashSet;
 import java.util.Map;
 import java.util.Set;
+import java.util.function.Supplier;
 
 import org.springframework.beans.BeanMetadataAttributeAccessor;
 import org.springframework.beans.MutablePropertyValues;
@@ -165,6 +166,8 @@ public abstract class AbstractBeanDefinition extends BeanMetadataAttributeAccess
 
 	private MethodOverrides methodOverrides = new MethodOverrides();
 
+	private Supplier<?> instanceSupplier;
+
 	private String factoryBeanName;
 
 	private String factoryMethodName;
@@ -234,6 +237,7 @@ public abstract class AbstractBeanDefinition extends BeanMetadataAttributeAccess
 			setPrimary(originalAbd.isPrimary());
 			setNonPublicAccessAllowed(originalAbd.isNonPublicAccessAllowed());
 			setLenientConstructorResolution(originalAbd.isLenientConstructorResolution());
+			setInstanceSupplier(originalAbd.getInstanceSupplier());
 			setInitMethodName(originalAbd.getInitMethodName());
 			setEnforceInitMethod(originalAbd.isEnforceInitMethod());
 			setDestroyMethodName(originalAbd.getDestroyMethodName());
@@ -298,6 +302,7 @@ public abstract class AbstractBeanDefinition extends BeanMetadataAttributeAccess
 			setDependsOn(otherAbd.getDependsOn());
 			setNonPublicAccessAllowed(otherAbd.isNonPublicAccessAllowed());
 			setLenientConstructorResolution(otherAbd.isLenientConstructorResolution());
+			setInstanceSupplier(otherAbd.getInstanceSupplier());
 			if (StringUtils.hasLength(otherAbd.getInitMethodName())) {
 				setInitMethodName(otherAbd.getInitMethodName());
 				setEnforceInitMethod(otherAbd.isEnforceInitMethod());
@@ -738,6 +743,28 @@ public abstract class AbstractBeanDefinition extends BeanMetadataAttributeAccess
 	}
 
 
+	/**
+	 * Specify a callback for creating an instance of the bean,
+	 * as an alternative to a declaratively specified factory method.
+	 * <p>If such a callback is set, it will override any other constructor
+	 * or factory method metadata. However, bean property population and
+	 * potential annotation-driven injection will still apply as usual.
+	 * @since 5.0
+	 * @see #setConstructorArgumentValues(ConstructorArgumentValues)
+	 * @see #setPropertyValues(MutablePropertyValues)
+	 */
+	public void setInstanceSupplier(Supplier<?> instanceSupplier) {
+		this.instanceSupplier = instanceSupplier;
+	}
+
+	/**
+	 * Return a callback for creating an instance of the bean, if any.
+	 * @since 5.0
+	 */
+	public Supplier<?> getInstanceSupplier() {
+		return this.instanceSupplier;
+	}
+
 	@Override
 	public void setFactoryBeanName(String factoryBeanName) {
 		this.factoryBeanName = factoryBeanName;

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

@@ -22,6 +22,7 @@ import java.lang.reflect.Member;
 import java.lang.reflect.Method;
 import java.util.HashSet;
 import java.util.Set;
+import java.util.function.Supplier;
 
 import org.springframework.beans.MutablePropertyValues;
 import org.springframework.beans.factory.config.BeanDefinition;
@@ -116,12 +117,45 @@ public class RootBeanDefinition extends AbstractBeanDefinition {
 	/**
 	 * Create a new RootBeanDefinition for a singleton.
 	 * @param beanClass the class of the bean to instantiate
+	 * @see #setBeanClass
 	 */
 	public RootBeanDefinition(Class<?> beanClass) {
 		super();
 		setBeanClass(beanClass);
 	}
 
+	/**
+	 * Create a new RootBeanDefinition for a singleton bean, constructing each instance
+	 * through calling the given supplier (possibly a lambda or method reference).
+	 * @param beanClass the class of the bean to instantiate
+	 * @param instanceSupplier the supplier to construct a bean instance,
+	 * as an alternative to a declaratively specified factory method
+	 * @since 5.0
+	 * @see #setInstanceSupplier(Supplier)
+	 */
+	public <T> RootBeanDefinition(Class<T> beanClass, Supplier<T> instanceSupplier) {
+		super();
+		setBeanClass(beanClass);
+		setInstanceSupplier(instanceSupplier);
+	}
+
+	/**
+	 * Create a new RootBeanDefinition for a scoped bean, constructing each instance
+	 * through calling the given supplier (possibly a lambda or method reference).
+	 * @param beanClass the class of the bean to instantiate
+	 * @param scope the name of the corresponding scope
+	 * @param instanceSupplier the supplier to construct a bean instance,
+	 * as an alternative to a declaratively specified factory method
+	 * @since 5.0
+	 * @see #setInstanceSupplier(Supplier)
+	 */
+	public <T> RootBeanDefinition(Class<T> beanClass, String scope, Supplier<T> instanceSupplier) {
+		super();
+		setBeanClass(beanClass);
+		setScope(scope);
+		setInstanceSupplier(instanceSupplier);
+	}
+
 	/**
 	 * Create a new RootBeanDefinition for a singleton,
 	 * using the given autowire mode.

spring-context/src/test/java/org/springframework/context/support/GenericApplicationContextTests.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2015 the original author or authors.
+ * Copyright 2002-2016 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.
@@ -43,6 +43,7 @@ public class GenericApplicationContextTests {
 		ac.registerBeanDefinition("testBean", new RootBeanDefinition(String.class));
 		ac.refresh();
 
+		assertEquals("", ac.getBean("testBean"));
 		assertSame(ac.getBean("testBean"), ac.getBean(String.class));
 		assertSame(ac.getBean("testBean"), ac.getBean(CharSequence.class));
 
@@ -55,6 +56,31 @@ public class GenericApplicationContextTests {
 		}
 	}
 
+	@Test
+	public void withSingletonSupplier() {
+		GenericApplicationContext ac = new GenericApplicationContext();
+		ac.registerBeanDefinition("testBean", new RootBeanDefinition(String.class, ac::toString));
+		ac.refresh();
+
+		assertSame(ac.getBean("testBean"), ac.getBean("testBean"));
+		assertSame(ac.getBean("testBean"), ac.getBean(String.class));
+		assertSame(ac.getBean("testBean"), ac.getBean(CharSequence.class));
+		assertEquals(ac.toString(), ac.getBean("testBean"));
+	}
+
+	@Test
+	public void withScopedSupplier() {
+		GenericApplicationContext ac = new GenericApplicationContext();
+		ac.registerBeanDefinition("testBean",
+				new RootBeanDefinition(String.class, RootBeanDefinition.SCOPE_PROTOTYPE, ac::toString));
+		ac.refresh();
+
+		assertNotSame(ac.getBean("testBean"), ac.getBean("testBean"));
+		assertEquals(ac.getBean("testBean"), ac.getBean(String.class));
+		assertEquals(ac.getBean("testBean"), ac.getBean(CharSequence.class));
+		assertEquals(ac.toString(), ac.getBean("testBean"));
+	}
+
 	@Test
 	public void accessAfterClosing() {
 		GenericApplicationContext ac = new GenericApplicationContext();