Optimize memory usage in factory *Metadata classes

InjectionMetadata and LifecycleMetadata can end up having mostly empty
instance variables. In such cases memory usage can be improved a little
bit.

This patch addresses this in two ways:

 - Creating a LinkedHashSet of the "right" size, the default capacity
   is 16 but the exact capacity needed is known in advance.

 - If the argument is empty then use Collections#emptySet which is a
   constant so no additional memory is used. Since it's immutable there
   is no need for the Collections#synchronizedSet wrapper.

Issue: SPR-9264

spring-beans/src/main/java/org/springframework/beans/factory/annotation/InitDestroyAnnotationBeanPostProcessor.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2011 the original author or authors.
+ * Copyright 2002-2012 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.
@@ -247,20 +247,30 @@ public class InitDestroyAnnotationBeanPostProcessor
 		public LifecycleMetadata(Class<?> targetClass, Collection<LifecycleElement> initMethods,
 				Collection<LifecycleElement> destroyMethods) {
 
-			this.initMethods = Collections.synchronizedSet(new LinkedHashSet<LifecycleElement>());
-			for (LifecycleElement element : initMethods) {
-				if (logger.isDebugEnabled()) {
-					logger.debug("Found init method on class [" + targetClass.getName() + "]: " + element);
+			if (!initMethods.isEmpty()) {
+				this.initMethods = Collections.synchronizedSet(new LinkedHashSet<LifecycleElement>(initMethods.size()));
+				for (LifecycleElement element : initMethods) {
+					if (logger.isDebugEnabled()) {
+						logger.debug("Found init method on class [" + targetClass.getName() + "]: " + element);
+					}
+					this.initMethods.add(element);
 				}
-				this.initMethods.add(element);
+			}
+			else {
+				this.initMethods = Collections.emptySet();
 			}
 
-			this.destroyMethods = Collections.synchronizedSet(new LinkedHashSet<LifecycleElement>());
-			for (LifecycleElement element : destroyMethods) {
-				if (logger.isDebugEnabled()) {
-					logger.debug("Found destroy method on class [" + targetClass.getName() + "]: " + element);
+			if (!destroyMethods.isEmpty()) {
+				this.destroyMethods = Collections.synchronizedSet(new LinkedHashSet<LifecycleElement>(destroyMethods.size()));
+				for (LifecycleElement element : destroyMethods) {
+					if (logger.isDebugEnabled()) {
+						logger.debug("Found destroy method on class [" + targetClass.getName() + "]: " + element);
+					}
+					this.destroyMethods.add(element);
 				}
-				this.destroyMethods.add(element);
+			}
+			else {
+				this.destroyMethods = Collections.emptySet();
 			}
 		}
 

spring-beans/src/main/java/org/springframework/beans/factory/annotation/InjectionMetadata.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2011 the original author or authors.
+ * Copyright 2002-2012 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.
@@ -54,12 +54,17 @@ public class InjectionMetadata {
 
 
 	public InjectionMetadata(Class targetClass, Collection<InjectedElement> elements) {
-		this.injectedElements = Collections.synchronizedSet(new LinkedHashSet<InjectedElement>());
-		for (InjectedElement element : elements) {
-			if (logger.isDebugEnabled()) {
-				logger.debug("Found injected element on class [" + targetClass.getName() + "]: " + element);
+		if (!elements.isEmpty()) {
+			this.injectedElements = Collections.synchronizedSet(new LinkedHashSet<InjectedElement>(elements.size()));
+			for (InjectedElement element : elements) {
+				if (logger.isDebugEnabled()) {
+					logger.debug("Found injected element on class [" + targetClass.getName() + "]: " + element);
+				}
+				this.injectedElements.add(element);
 			}
-			this.injectedElements.add(element);
+		}
+		else {
+			this.injectedElements = Collections.emptySet();
 		}
 	}