FactoryBean, BeanPostProcessor and HandlerInterceptor variants declared with default methods

Issue: SPR-14432

spring-beans/src/main/java/org/springframework/beans/factory/FactoryBean.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2012 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.
@@ -111,10 +111,14 @@ public interface FactoryBean<T> {
 	 * implementations which do not implement this extended interface are
 	 * simply assumed to always return independent instances if the
 	 * {@code isSingleton()} implementation returns {@code false}.
+	 * <p>The default implementation returns {@code true}, since a
+	 * {@code FactoryBean} typically manages a singleton instance.
 	 * @return whether the exposed object is a singleton
 	 * @see #getObject()
 	 * @see SmartFactoryBean#isPrototype()
 	 */
-	boolean isSingleton();
+	default boolean isSingleton() {
+		return true;
+	}
 
 }

spring-beans/src/main/java/org/springframework/beans/factory/ObjectFactory.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2012 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.
@@ -35,6 +35,7 @@ import org.springframework.beans.BeansException;
  * @since 1.0.2
  * @see FactoryBean
  */
+@FunctionalInterface
 public interface ObjectFactory<T> {
 
 	/**

spring-beans/src/main/java/org/springframework/beans/factory/SmartFactoryBean.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2012 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.
@@ -50,11 +50,14 @@ public interface SmartFactoryBean<T> extends FactoryBean<T> {
 	 * it should not return {@code true} for scoped objects or other
 	 * kinds of non-singleton, non-independent objects. For this reason,
 	 * this is not simply the inverted form of {@link #isSingleton()}.
+	 * <p>The default implementation returns {@code false}.
 	 * @return whether the exposed object is a prototype
 	 * @see #getObject()
 	 * @see #isSingleton()
 	 */
-	boolean isPrototype();
+	default boolean isPrototype() {
+		return false;
+	}
 
 	/**
 	 * Does this FactoryBean expect eager initialization, that is,
@@ -67,9 +70,12 @@ public interface SmartFactoryBean<T> extends FactoryBean<T> {
 	 * also applying post-processors eagerly. This may make sense in case
 	 * of a {@link #isSingleton() singleton} object, in particular if
 	 * post-processors expect to be applied on startup.
+	 * <p>The default implementation returns {@code false}.
 	 * @return whether eager initialization applies
 	 * @see org.springframework.beans.factory.config.ConfigurableListableBeanFactory#preInstantiateSingletons()
 	 */
-	boolean isEagerInit();
+	default boolean isEagerInit() {
+		return false;
+	}
 
 }

spring-beans/src/main/java/org/springframework/beans/factory/config/BeanPostProcessor.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.
@@ -46,6 +46,7 @@ public interface BeanPostProcessor {
 	 * initialization callbacks (like InitializingBean's {@code afterPropertiesSet}
 	 * or a custom init-method). The bean will already be populated with property values.
 	 * The returned bean instance may be a wrapper around the original.
+	 * <p>The default implementation returns the given {@code bean} as-is.
 	 * @param bean the new bean instance
 	 * @param beanName the name of the bean
 	 * @return the bean instance to use, either the original or a wrapped one;
@@ -53,7 +54,9 @@ public interface BeanPostProcessor {
 	 * @throws org.springframework.beans.BeansException in case of errors
 	 * @see org.springframework.beans.factory.InitializingBean#afterPropertiesSet
 	 */
-	Object postProcessBeforeInitialization(Object bean, String beanName) throws BeansException;
+	default Object postProcessBeforeInitialization(Object bean, String beanName) throws BeansException {
+		return bean;
+	}
 
 	/**
 	 * Apply this BeanPostProcessor to the given new bean instance <i>after</i> any bean
@@ -67,6 +70,7 @@ public interface BeanPostProcessor {
 	 * <p>This callback will also be invoked after a short-circuiting triggered by a
 	 * {@link InstantiationAwareBeanPostProcessor#postProcessBeforeInstantiation} method,
 	 * in contrast to all other BeanPostProcessor callbacks.
+	 * <p>The default implementation returns the given {@code bean} as-is.
 	 * @param bean the new bean instance
 	 * @param beanName the name of the bean
 	 * @return the bean instance to use, either the original or a wrapped one;
@@ -75,6 +79,8 @@ public interface BeanPostProcessor {
 	 * @see org.springframework.beans.factory.InitializingBean#afterPropertiesSet
 	 * @see org.springframework.beans.factory.FactoryBean
 	 */
-	Object postProcessAfterInitialization(Object bean, String beanName) throws BeansException;
+	default Object postProcessAfterInitialization(Object bean, String beanName) throws BeansException {
+		return bean;
+	}
 
 }

spring-beans/src/main/java/org/springframework/beans/factory/config/DestructionAwareBeanPostProcessor.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.
@@ -61,6 +61,8 @@ public interface DestructionAwareBeanPostProcessor extends BeanPostProcessor {
 	 * be called for this bean instance eventually, or {@code false} if not needed
 	 * @since 4.3
 	 */
-	boolean requiresDestruction(Object bean);
+	default boolean requiresDestruction(Object bean) {
+		return true;
+	}
 
 }

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

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2012 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.
@@ -58,6 +58,7 @@ public interface InstantiationAwareBeanPostProcessor extends BeanPostProcessor {
 	 * <p>Post-processors may implement the extended
 	 * {@link SmartInstantiationAwareBeanPostProcessor} interface in order
 	 * to predict the type of the bean object that they are going to return here.
+	 * <p>The default implementation returns {@code null}.
 	 * @param beanClass the class of the bean to be instantiated
 	 * @param beanName the name of the bean
 	 * @return the bean object to expose instead of a default instance of the target bean,
@@ -66,7 +67,9 @@ public interface InstantiationAwareBeanPostProcessor extends BeanPostProcessor {
 	 * @see org.springframework.beans.factory.support.AbstractBeanDefinition#hasBeanClass
 	 * @see org.springframework.beans.factory.support.AbstractBeanDefinition#getFactoryMethodName
 	 */
-	Object postProcessBeforeInstantiation(Class<?> beanClass, String beanName) throws BeansException;
+	default Object postProcessBeforeInstantiation(Class<?> beanClass, String beanName) throws BeansException {
+		return null;
+	}
 
 	/**
 	 * Perform operations after the bean has been instantiated, via a constructor or factory method,
@@ -74,6 +77,7 @@ public interface InstantiationAwareBeanPostProcessor extends BeanPostProcessor {
 	 * <p>This is the ideal callback for performing field injection on the given bean instance.
 	 * See Spring's own {@link org.springframework.beans.factory.annotation.AutowiredAnnotationBeanPostProcessor}
 	 * for a typical example.
+	 * <p>The default implementation returns {@code true}.
 	 * @param bean the bean instance created, with properties not having been set yet
 	 * @param beanName the name of the bean
 	 * @return {@code true} if properties should be set on the bean; {@code false}
@@ -82,7 +86,9 @@ public interface InstantiationAwareBeanPostProcessor extends BeanPostProcessor {
 	 * instances being invoked on this bean instance.
 	 * @throws org.springframework.beans.BeansException in case of errors
 	 */
-	boolean postProcessAfterInstantiation(Object bean, String beanName) throws BeansException;
+	default boolean postProcessAfterInstantiation(Object bean, String beanName) throws BeansException {
+		return true;
+	}
 
 	/**
 	 * Post-process the given property values before the factory applies them
@@ -91,6 +97,7 @@ public interface InstantiationAwareBeanPostProcessor extends BeanPostProcessor {
 	 * <p>Also allows for replacing the property values to apply, typically through
 	 * creating a new MutablePropertyValues instance based on the original PropertyValues,
 	 * adding or removing specific values.
+	 * <p>The default implementation returns the given {@code pvs} as-is.
 	 * @param pvs the property values that the factory is about to apply (never {@code null})
 	 * @param pds the relevant property descriptors for the target bean (with ignored
 	 * dependency types - which the factory handles specifically - already filtered out)
@@ -102,8 +109,10 @@ public interface InstantiationAwareBeanPostProcessor extends BeanPostProcessor {
 	 * @throws org.springframework.beans.BeansException in case of errors
 	 * @see org.springframework.beans.MutablePropertyValues
 	 */
-	PropertyValues postProcessPropertyValues(
+	default PropertyValues postProcessPropertyValues(
-			PropertyValues pvs, PropertyDescriptor[] pds, Object bean, String beanName)
+			PropertyValues pvs, PropertyDescriptor[] pds, Object bean, String beanName) throws BeansException {
-			throws BeansException;
+
+		return pvs;
+	}
 
 }

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

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2012 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.
@@ -39,21 +39,29 @@ public interface SmartInstantiationAwareBeanPostProcessor extends InstantiationA
 	/**
 	 * Predict the type of the bean to be eventually returned from this
 	 * processor's {@link #postProcessBeforeInstantiation} callback.
+	 * <p>The default implementation returns {@code null}.
 	 * @param beanClass the raw class of the bean
 	 * @param beanName the name of the bean
 	 * @return the type of the bean, or {@code null} if not predictable
 	 * @throws org.springframework.beans.BeansException in case of errors
 	 */
-	Class<?> predictBeanType(Class<?> beanClass, String beanName) throws BeansException;
+	default Class<?> predictBeanType(Class<?> beanClass, String beanName) throws BeansException {
+		return null;
+	}
 
 	/**
 	 * Determine the candidate constructors to use for the given bean.
+	 * <p>The default implementation returns {@code null}.
 	 * @param beanClass the raw class of the bean (never {@code null})
 	 * @param beanName the name of the bean
 	 * @return the candidate constructors, or {@code null} if none specified
 	 * @throws org.springframework.beans.BeansException in case of errors
 	 */
-	Constructor<?>[] determineCandidateConstructors(Class<?> beanClass, String beanName) throws BeansException;
+	default Constructor<?>[] determineCandidateConstructors(Class<?> beanClass, String beanName)
+			throws BeansException {
+
+		return null;
+	}
 
 	/**
 	 * Obtain a reference for early access to the specified bean,
@@ -69,12 +77,15 @@ public interface SmartInstantiationAwareBeanPostProcessor extends InstantiationA
 	 * return the raw bean instance from those subsequent callbacks (if the wrapper
 	 * for the affected bean has been built for a call to this method already,
 	 * it will be exposes as final bean reference by default).
+	 * <p>The default implementation returns the given {@code bean} as-is.
 	 * @param bean the raw bean instance
 	 * @param beanName the name of the bean
 	 * @return the object to expose as bean reference
 	 * (typically with the passed-in bean instance as default)
 	 * @throws org.springframework.beans.BeansException in case of errors
 	 */
-	Object getEarlyBeanReference(Object bean, String beanName) throws BeansException;
+	default Object getEarlyBeanReference(Object bean, String beanName) throws BeansException {
+		return bean;
+	}
 
 }

spring-webmvc/src/main/java/org/springframework/web/servlet/HandlerInterceptor.java

@@ -84,6 +84,7 @@ public interface HandlerInterceptor {
 	 * <p><strong>Note:</strong> special considerations apply for asynchronous
 	 * request processing. For more details see
 	 * {@link org.springframework.web.servlet.AsyncHandlerInterceptor}.
+	 * <p>The default implementation returns {@code true}.
 	 * @param request current HTTP request
 	 * @param response current HTTP response
 	 * @param handler chosen handler to execute, for type and/or instance evaluation
@@ -92,8 +93,11 @@ public interface HandlerInterceptor {
 	 * that this interceptor has already dealt with the response itself.
 	 * @throws Exception in case of errors
 	 */
-	boolean preHandle(HttpServletRequest request, HttpServletResponse response, Object handler)
+	default boolean preHandle(HttpServletRequest request, HttpServletResponse response, Object handler)
-	    throws Exception;
+			throws Exception {
+
+		return true;
+	}
 
 	/**
 	 * Intercept the execution of a handler. Called after HandlerAdapter actually
@@ -106,6 +110,7 @@ public interface HandlerInterceptor {
 	 * <p><strong>Note:</strong> special considerations apply for asynchronous
 	 * request processing. For more details see
 	 * {@link org.springframework.web.servlet.AsyncHandlerInterceptor}.
+	 * <p>The default implementation is empty.
 	 * @param request current HTTP request
 	 * @param response current HTTP response
 	 * @param handler handler (or {@link HandlerMethod}) that started asynchronous
@@ -114,8 +119,10 @@ public interface HandlerInterceptor {
 	 * (can also be {@code null})
 	 * @throws Exception in case of errors
 	 */
-	void postHandle(HttpServletRequest request, HttpServletResponse response, Object handler, ModelAndView modelAndView)
+	default void postHandle(
-			throws Exception;
+			HttpServletRequest request, HttpServletResponse response, Object handler, ModelAndView modelAndView)
+			throws Exception {
+	}
 
 	/**
 	 * Callback after completion of request processing, that is, after rendering
@@ -129,6 +136,7 @@ public interface HandlerInterceptor {
 	 * <p><strong>Note:</strong> special considerations apply for asynchronous
 	 * request processing. For more details see
 	 * {@link org.springframework.web.servlet.AsyncHandlerInterceptor}.
+	 * <p>The default implementation is empty.
 	 * @param request current HTTP request
 	 * @param response current HTTP response
 	 * @param handler handler (or {@link HandlerMethod}) that started asynchronous
@@ -136,7 +144,9 @@ public interface HandlerInterceptor {
 	 * @param ex exception thrown on handler execution, if any
 	 * @throws Exception in case of errors
 	 */
-	void afterCompletion(HttpServletRequest request, HttpServletResponse response, Object handler, Exception ex)
+	default void afterCompletion(
-			throws Exception;
+			HttpServletRequest request, HttpServletResponse response, Object handler, Exception ex)
+			throws Exception {
+	}
 
 }