Provide a flag to disable XML support

This commit introduces a spring.xml.ignore system property
which when set to true avoid initializing XML infrastructure.

A typical use case is optimizing GraalVM native image footprint
for applications not using XML. In order to be effective, those
classes should be initialized at build time:

- org.springframework.util.DefaultPropertiesPersister
- org.springframework.core.io.support.PropertiesLoaderUtils
- org.springframework.web.servlet.function.support.RouterFunctionMapping
- org.springframework.web.client.RestTemplate
- org.springframework.web.servlet.mvc.method.annotation.ExceptionHandlerExceptionResolver
- org.springframework.web.servlet.config.annotation.WebMvcConfigurationSupport
- org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter
- org.springframework.http.converter.support.AllEncompassingFormHttpMessageConverter
- org.springframework.http.codec.support.BaseDefaultCodecs
- org.springframework.beans.PropertyEditorRegistrySupport

Closes gh-25151

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

@@ -24,6 +24,7 @@ import java.net.URLConnection;
 import java.util.Enumeration;
 import java.util.Properties;
 
+import org.springframework.core.SpringProperties;
 import org.springframework.core.io.Resource;
 import org.springframework.lang.Nullable;
 import org.springframework.util.Assert;
@@ -41,6 +42,7 @@ import org.springframework.util.ResourceUtils;
  *
  * @author Juergen Hoeller
  * @author Rob Harrop
+ * @author Sebastien Deleuze
  * @since 2.0
  * @see PropertiesLoaderSupport
  */
@@ -48,6 +50,13 @@ public abstract class PropertiesLoaderUtils {
 
 	private static final String XML_FILE_EXTENSION = ".xml";
 
+	/**
+	 * Boolean flag controlled by a {@code spring.xml.ignore} system property that instructs Spring to
+	 * ignore XML, i.e. to not initialize the XML-related infrastructure.
+	 * <p>The default is "false".
+	 */
+	private static final boolean shouldIgnoreXml = SpringProperties.getFlag("spring.xml.ignore");
+
 
 	/**
 	 * Load properties from the given EncodedResource,
@@ -88,6 +97,9 @@ public abstract class PropertiesLoaderUtils {
 		try {
 			String filename = resource.getResource().getFilename();
 			if (filename != null && filename.endsWith(XML_FILE_EXTENSION)) {
+				if (shouldIgnoreXml) {
+					throw new UnsupportedOperationException("XML support disabled");
+				}
 				stream = resource.getInputStream();
 				persister.loadFromXml(props, stream);
 			}
@@ -133,6 +145,9 @@ public abstract class PropertiesLoaderUtils {
 		try (InputStream is = resource.getInputStream()) {
 			String filename = resource.getFilename();
 			if (filename != null && filename.endsWith(XML_FILE_EXTENSION)) {
+				if (shouldIgnoreXml) {
+					throw new UnsupportedOperationException("XML support disabled");
+				}
 				props.loadFromXML(is);
 			}
 			else {
@@ -180,6 +195,9 @@ public abstract class PropertiesLoaderUtils {
 			ResourceUtils.useCachesIfNecessary(con);
 			try (InputStream is = con.getInputStream()) {
 				if (resourceName.endsWith(XML_FILE_EXTENSION)) {
+					if (shouldIgnoreXml) {
+						throw new UnsupportedOperationException("XML support disabled");
+					}
 					props.loadFromXML(is);
 				}
 				else {

spring-core/src/main/java/org/springframework/util/DefaultPropertiesPersister.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2019 the original author or authors.
+ * Copyright 2002-2020 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.
@@ -23,6 +23,8 @@ import java.io.Reader;
 import java.io.Writer;
 import java.util.Properties;
 
+import org.springframework.core.SpringProperties;
+
 /**
  * Default implementation of the {@link PropertiesPersister} interface.
  * Follows the native parsing of {@code java.util.Properties}.
@@ -46,6 +48,7 @@ import java.util.Properties;
  * "defaultEncoding" and "fileEncodings" properties).
  *
  * @author Juergen Hoeller
+ * @author Sebastien Deleuze
  * @since 10.03.2004
  * @see java.util.Properties
  * @see java.util.Properties#load
@@ -53,6 +56,14 @@ import java.util.Properties;
  */
 public class DefaultPropertiesPersister implements PropertiesPersister {
 
+	/**
+	 * Boolean flag controlled by a {@code spring.xml.ignore} system property that instructs Spring to
+	 * ignore XML, i.e. to not initialize the XML-related infrastructure.
+	 * <p>The default is "false".
+	 */
+	private static final boolean shouldIgnoreXml = SpringProperties.getFlag("spring.xml.ignore");
+
+
 	@Override
 	public void load(Properties props, InputStream is) throws IOException {
 		props.load(is);
@@ -75,16 +86,25 @@ public class DefaultPropertiesPersister implements PropertiesPersister {
 
 	@Override
 	public void loadFromXml(Properties props, InputStream is) throws IOException {
+		if (shouldIgnoreXml) {
+			throw new UnsupportedOperationException("XML support disabled");
+		}
 		props.loadFromXML(is);
 	}
 
 	@Override
 	public void storeToXml(Properties props, OutputStream os, String header) throws IOException {
+		if (shouldIgnoreXml) {
+			throw new UnsupportedOperationException("XML support disabled");
+		}
 		props.storeToXML(os, header);
 	}
 
 	@Override
 	public void storeToXml(Properties props, OutputStream os, String header, String encoding) throws IOException {
+		if (shouldIgnoreXml) {
+			throw new UnsupportedOperationException("XML support disabled");
+		}
 		props.storeToXML(os, header, encoding);
 	}