Consistent local vs external resolution of https schema references

Co-Authored-By: Sam Brannen <sbrannen@pivotal.io>

See gh-22504

spring-beans/src/main/java/org/springframework/beans/factory/xml/PluggableSchemaResolver.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.
@@ -37,18 +37,18 @@ import org.springframework.util.CollectionUtils;
  * {@link EntityResolver} implementation that attempts to resolve schema URLs into
  * local {@link ClassPathResource classpath resources} using a set of mappings files.
  *
- * <p>By default, this class will look for mapping files in the classpath using the pattern:
- * {@code META-INF/spring.schemas} allowing for multiple files to exist on the
- * classpath at any one time.
+ * <p>By default, this class will look for mapping files in the classpath using the
+ * pattern: {@code META-INF/spring.schemas} allowing for multiple files to exist on
+ * the classpath at any one time.
  *
- * The format of {@code META-INF/spring.schemas} is a properties
- * file where each line should be of the form {@code systemId=schema-location}
- * where {@code schema-location} should also be a schema file in the classpath.
- * Since systemId is commonly a URL, one must be careful to escape any ':' characters
- * which are treated as delimiters in properties files.
+ * <p>The format of {@code META-INF/spring.schemas} is a properties file where each line
+ * should be of the form {@code systemId=schema-location} where {@code schema-location}
+ * should also be a schema file in the classpath. Since {@code systemId} is commonly a
+ * URL, one must be careful to escape any ':' characters which are treated as delimiters
+ * in properties files.
  *
- * <p>The pattern for the mapping files can be overidden using the
- * {@link #PluggableSchemaResolver(ClassLoader, String)} constructor
+ * <p>The pattern for the mapping files can be overridden using the
+ * {@link #PluggableSchemaResolver(ClassLoader, String)} constructor.
  *
  * @author Rob Harrop
  * @author Juergen Hoeller
@@ -109,6 +109,10 @@ public class PluggableSchemaResolver implements EntityResolver {
 
 		if (systemId != null) {
 			String resourceLocation = getSchemaMappings().get(systemId);
+			if (resourceLocation == null && systemId.startsWith("https:")) {
+				// Retrieve canonical http schema mapping even for https declaration
+				resourceLocation = getSchemaMappings().get("http:" + systemId.substring(6));
+			}
 			if (resourceLocation != null) {
 				Resource resource = new ClassPathResource(resourceLocation, this.classLoader);
 				try {