Support for fine-grained by-type references and autowired properties

Closes gh-23032

Author: jhoeller

spring-beans/src/main/java/org/springframework/beans/BeanMetadataElement.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2012 the original author or authors.
+ * Copyright 2002-2019 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.
@@ -32,6 +32,8 @@ public interface BeanMetadataElement {
 	 * (may be {@code null}).
 	 */
 	@Nullable
-	Object getSource();
+	default Object getSource() {
+		return null;
+	}
 
 }

spring-beans/src/main/java/org/springframework/beans/factory/config/AutowiredPropertyMarker.java

@@ -0,0 +1,68 @@
+/*
+ * Copyright 2002-2019 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.
+ * You may obtain a copy of the License at
+ *
+ *      https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.springframework.beans.factory.config;
+
+import java.io.Serializable;
+
+import org.springframework.lang.Nullable;
+
+/**
+ * Simple marker class for an individually autowired property value, to be added
+ * to {@link BeanDefinition#getPropertyValues()} for a specific bean property.
+ *
+ * <p>At runtime, this will be replaced with a {@link DependencyDescriptor}
+ * for the corresponding bean property's write method, eventually to be resolved
+ * through a {@link AutowireCapableBeanFactory#resolveDependency} step.
+ *
+ * @author Juergen Hoeller
+ * @since 5.2
+ * @see AutowireCapableBeanFactory#resolveDependency
+ * @see BeanDefinition#getPropertyValues()
+ * @see org.springframework.beans.factory.support.BeanDefinitionBuilder#addAutowiredProperty
+ */
+public final class AutowiredPropertyMarker implements Serializable {
+
+	/**
+	 * The canonical instance for the autowired marker value.
+	 */
+	public static final Object INSTANCE = new AutowiredPropertyMarker();
+
+
+	private AutowiredPropertyMarker() {
+	}
+
+	private Object readResolve() {
+		return INSTANCE;
+	}
+
+
+	@Override
+	public boolean equals(@Nullable Object obj) {
+		return (this == obj);
+	}
+
+	@Override
+	public int hashCode() {
+		return AutowiredPropertyMarker.class.hashCode();
+	}
+
+	@Override
+	public String toString() {
+		return "(autowired)";
+	}
+
+}

spring-beans/src/main/java/org/springframework/beans/factory/config/RuntimeBeanReference.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2017 the original author or authors.
+ * Copyright 2002-2019 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.
@@ -26,22 +26,24 @@
  * @author Rod Johnson
  * @author Juergen Hoeller
  * @see BeanDefinition#getPropertyValues()
- * @see org.springframework.beans.factory.BeanFactory#getBean
+ * @see org.springframework.beans.factory.BeanFactory#getBean(String)
+ * @see org.springframework.beans.factory.BeanFactory#getBean(Class)
  */
 public class RuntimeBeanReference implements BeanReference {
 
 	private final String beanName;
 
+	@Nullable
+	private final Class<?> beanType;
+
 	private final boolean toParent;
 
 	@Nullable
 	private Object source;
 
 
 	/**
-	 * Create a new RuntimeBeanReference to the given bean name,
-	 * without explicitly marking it as reference to a bean in
-	 * the parent factory.
+	 * Create a new RuntimeBeanReference to the given bean name.
 	 * @param beanName name of the target bean
 	 */
 	public RuntimeBeanReference(String beanName) {
@@ -50,27 +52,64 @@ public RuntimeBeanReference(String beanName) {
 
 	/**
 	 * Create a new RuntimeBeanReference to the given bean name,
-	 * with the option to mark it as reference to a bean in
-	 * the parent factory.
+	 * with the option to mark it as reference to a bean in the parent factory.
 	 * @param beanName name of the target bean
-	 * @param toParent whether this is an explicit reference to
-	 * a bean in the parent factory
+	 * @param toParent whether this is an explicit reference to a bean in the
+	 * parent factory
 	 */
 	public RuntimeBeanReference(String beanName, boolean toParent) {
 		Assert.hasText(beanName, "'beanName' must not be empty");
 		this.beanName = beanName;
+		this.beanType = null;
 		this.toParent = toParent;
 	}
 
+	/**
+	 * Create a new RuntimeBeanReference to a bean of the given type.
+	 * @param beanType type of the target bean
+	 * @since 5.2
+	 */
+	public RuntimeBeanReference(Class<?> beanType) {
+		this(beanType, false);
+	}
 
+	/**
+	 * Create a new RuntimeBeanReference to a bean of the given type,
+	 * with the option to mark it as reference to a bean in the parent factory.
+	 * @param beanType type of the target bean
+	 * @param toParent whether this is an explicit reference to a bean in the
+	 * parent factory
+	 * @since 5.2
+	 */
+	public RuntimeBeanReference(Class<?> beanType, boolean toParent) {
+		Assert.notNull(beanType, "'beanType' must not be empty");
+		this.beanName = beanType.getName();
+		this.beanType = beanType;
+		this.toParent = toParent;
+	}
+
+
+	/**
+	 * Return the requested bean name, or the fully-qualified type name
+	 * in case of by-type resolution.
+	 * @see #getBeanType()
+	 */
 	@Override
 	public String getBeanName() {
 		return this.beanName;
 	}
 
 	/**
-	 * Return whether this is an explicit reference to a bean
-	 * in the parent factory.
+	 * Return the requested bean type if resolution by type is demanded.
+	 * @since 5.2
+	 */
+	@Nullable
+	public Class<?> getBeanType() {
+		return this.beanType;
+	}
+
+	/**
+	 * Return whether this is an explicit reference to a bean in the parent factory.
 	 */
 	public boolean isToParent() {
 		return this.toParent;
@@ -100,7 +139,8 @@ public boolean equals(@Nullable Object other) {
 			return false;
 		}
 		RuntimeBeanReference that = (RuntimeBeanReference) other;
-		return (this.beanName.equals(that.beanName) && this.toParent == that.toParent);
+		return (this.beanName.equals(that.beanName) && this.beanType == that.beanType &&
+				this.toParent == that.toParent);
 	}
 
 	@Override

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

@@ -61,6 +61,7 @@
 import org.springframework.beans.factory.InjectionPoint;
 import org.springframework.beans.factory.UnsatisfiedDependencyException;
 import org.springframework.beans.factory.config.AutowireCapableBeanFactory;
+import org.springframework.beans.factory.config.AutowiredPropertyMarker;
 import org.springframework.beans.factory.config.BeanDefinition;
 import org.springframework.beans.factory.config.BeanPostProcessor;
 import org.springframework.beans.factory.config.ConfigurableBeanFactory;
@@ -1683,6 +1684,13 @@ protected void applyPropertyValues(String beanName, BeanDefinition mbd, BeanWrap
 			else {
 				String propertyName = pv.getName();
 				Object originalValue = pv.getValue();
+				if (originalValue == AutowiredPropertyMarker.INSTANCE) {
+					Method writeMethod = bw.getPropertyDescriptor(propertyName).getWriteMethod();
+					if (writeMethod == null) {
+						throw new IllegalArgumentException("Autowire marker for property without write method: " + pv);
+					}
+					originalValue = new DependencyDescriptor(new MethodParameter(writeMethod, 0), true);
+				}
 				Object resolvedValue = valueResolver.resolveValueIfNecessary(pv, originalValue);
 				Object convertedValue = resolvedValue;
 				boolean convertible = bw.isWritableProperty(propertyName) &&

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

@@ -18,6 +18,7 @@
 
 import java.util.function.Supplier;
 
+import org.springframework.beans.factory.config.AutowiredPropertyMarker;
 import org.springframework.beans.factory.config.BeanDefinitionCustomizer;
 import org.springframework.beans.factory.config.RuntimeBeanReference;
 import org.springframework.lang.Nullable;
@@ -209,7 +210,7 @@ public BeanDefinitionBuilder addConstructorArgReference(String beanName) {
 	}
 
 	/**
-	 * Add the supplied property value under the given name.
+	 * Add the supplied property value under the given property name.
 	 */
 	public BeanDefinitionBuilder addPropertyValue(String name, @Nullable Object value) {
 		this.beanDefinition.getPropertyValues().add(name, value);
@@ -226,6 +227,17 @@ public BeanDefinitionBuilder addPropertyReference(String name, String beanName)
 		return this;
 	}
 
+	/**
+	 * Add an autowired marker for the specified property on the specified bean.
+	 * @param name the name of the property to mark as autowired
+	 * @since 5.2
+	 * @see AutowiredPropertyMarker
+	 */
+	public BeanDefinitionBuilder addAutowiredProperty(String name) {
+		this.beanDefinition.getPropertyValues().add(name, AutowiredPropertyMarker.INSTANCE);
+		return this;
+	}
+
 	/**
 	 * Set the init method for this definition.
 	 */