Cache SpringFactoriesLoader loads

Update `SpringFactoriesLoader` to cache property file loads. This helps
reduce the number of garbage objects created as each load uses an 8K
char buffer.

Issue: SPR-15509

Author: philwebb

spring-core/src/main/java/org/springframework/core/io/support/SpringFactoriesLoader.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2016 the original author or authors.
+ * Copyright 2002-2017 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.
@@ -20,17 +20,21 @@
 import java.net.URL;
 import java.util.ArrayList;
 import java.util.Arrays;
+import java.util.Collections;
 import java.util.Enumeration;
 import java.util.List;
+import java.util.Map;
 import java.util.Properties;
 
 import org.apache.commons.logging.Log;
 import org.apache.commons.logging.LogFactory;
-
 import org.springframework.core.annotation.AnnotationAwareOrderComparator;
 import org.springframework.core.io.UrlResource;
 import org.springframework.util.Assert;
 import org.springframework.util.ClassUtils;
+import org.springframework.util.ConcurrentReferenceHashMap;
+import org.springframework.util.LinkedMultiValueMap;
+import org.springframework.util.MultiValueMap;
 import org.springframework.util.ReflectionUtils;
 import org.springframework.util.StringUtils;
 
@@ -58,6 +62,8 @@ public abstract class SpringFactoriesLoader {
 
 	private static final Log logger = LogFactory.getLog(SpringFactoriesLoader.class);
 
+	private static Map<ClassLoader, MultiValueMap<String, String>> cache = new ConcurrentReferenceHashMap<>();
+
 	/**
 	 * The location to look for factories.
 	 * <p>Can be present in multiple JAR files.
@@ -107,21 +113,36 @@ public static <T> List<T> loadFactories(Class<T> factoryClass, ClassLoader class
 	 */
 	public static List<String> loadFactoryNames(Class<?> factoryClass, ClassLoader classLoader) {
 		String factoryClassName = factoryClass.getName();
+		return loadSpringFactories(classLoader).getOrDefault(factoryClassName,
+				Collections.emptyList());
+	}
+
+	private static Map<String, List<String>> loadSpringFactories(
+			ClassLoader classLoader) {
+		MultiValueMap<String, String> result = cache.get(classLoader);
+		if (result != null)
+			return result;
 		try {
-			Enumeration<URL> urls = (classLoader != null ? classLoader.getResources(FACTORIES_RESOURCE_LOCATION) :
-					ClassLoader.getSystemResources(FACTORIES_RESOURCE_LOCATION));
-			List<String> result = new ArrayList<>();
+			Enumeration<URL> urls = (classLoader != null
+					? classLoader.getResources(FACTORIES_RESOURCE_LOCATION)
+					: ClassLoader.getSystemResources(FACTORIES_RESOURCE_LOCATION));
+			result = new LinkedMultiValueMap<>();
 			while (urls.hasMoreElements()) {
 				URL url = urls.nextElement();
-				Properties properties = PropertiesLoaderUtils.loadProperties(new UrlResource(url));
-				String factoryClassNames = properties.getProperty(factoryClassName);
-				result.addAll(Arrays.asList(StringUtils.commaDelimitedListToStringArray(factoryClassNames)));
+				UrlResource resource = new UrlResource(url);
+				Properties properties = PropertiesLoaderUtils.loadProperties(resource);
+				for (Map.Entry<?, ?> entry : properties.entrySet()) {
+					List<String> factoryClassNames = Arrays.asList(
+							StringUtils.commaDelimitedListToStringArray((String) entry.getValue()));
+					result.addAll((String) entry.getKey(), factoryClassNames);
+				}
 			}
+			cache.put(classLoader, result);
 			return result;
 		}
 		catch (IOException ex) {
-			throw new IllegalArgumentException("Unable to load [" + factoryClass.getName() +
-					"] factories from location [" + FACTORIES_RESOURCE_LOCATION + "]", ex);
+			throw new IllegalArgumentException("Unable to load factories from location ["
+					+ FACTORIES_RESOURCE_LOCATION + "]", ex);
 		}
 	}