Use URLConnection caching defaults

In order to prevent leaks of large amounts of non-heap
memory (and potential other efficiency and performance side
effects), this commit turns ResourceUtils#useCachesIfNecessary
into a no-op method and deprecates it. It is recommended to
not use it anymore.

This method has been originally introduced via spring-projectsgh-9316 and
spring-projectsgh-13755 to avoid I/O failure during webapp hot reloading in
Servlet containers. This is not a popular deployment mode anymore
and we have not been able to reproduce the original issue with
a Java 17 JVM and Tomcat 10.

Closes spring-projectsgh-30955

spring-core/src/main/java/org/springframework/core/io/AbstractFileResolvingResource.java

@@ -297,14 +297,12 @@ public long lastModified() throws IOException {
 
 	/**
 	 * Customize the given {@link URLConnection} before fetching the resource.
-	 * <p>Calls {@link ResourceUtils#useCachesIfNecessary(URLConnection)} and
-	 * delegates to {@link #customizeConnection(HttpURLConnection)} if possible.
+	 * <p>Delegates to {@link #customizeConnection(HttpURLConnection)} if possible.
 	 * Can be overridden in subclasses.
 	 * @param con the URLConnection to customize
 	 * @throws IOException if thrown from URLConnection methods
 	 */
 	protected void customizeConnection(URLConnection con) throws IOException {
-		ResourceUtils.useCachesIfNecessary(con);
 		if (con instanceof HttpURLConnection httpConn) {
 			customizeConnection(httpConn);
 		}

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

@@ -680,7 +680,6 @@ protected Set<Resource> doFindPathMatchingJarResources(Resource rootDirResource,
 
 		if (con instanceof JarURLConnection jarCon) {
 			// Should usually be the case for traditional JAR files.
-			ResourceUtils.useCachesIfNecessary(jarCon);
 			jarFile = jarCon.getJarFile();
 			jarFileUrl = jarCon.getJarFileURL().toExternalForm();
 			JarEntry jarEntry = jarCon.getJarEntry();

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

@@ -30,7 +30,6 @@
 import org.springframework.util.ClassUtils;
 import org.springframework.util.DefaultPropertiesPersister;
 import org.springframework.util.PropertiesPersister;
-import org.springframework.util.ResourceUtils;
 
 /**
  * Convenient utility methods for loading of {@code java.util.Properties},
@@ -178,7 +177,6 @@ public static Properties loadAllProperties(String resourceName, @Nullable ClassL
 		while (urls.hasMoreElements()) {
 			URL url = urls.nextElement();
 			URLConnection con = url.openConnection();
-			ResourceUtils.useCachesIfNecessary(con);
 			try (InputStream is = con.getInputStream()) {
 				if (resourceName.endsWith(XML_FILE_EXTENSION)) {
 					props.loadFromXML(is);

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

@@ -421,13 +421,13 @@ public static URL toRelativeURL(URL root, String relativePath) throws MalformedU
 	}
 
 	/**
-	 * Set the {@link URLConnection#setUseCaches "useCaches"} flag on the
-	 * given connection, preferring {@code false} but leaving the
-	 * flag at {@code true} for JNLP based resources.
+	 * Leave the {@link URLConnection#setUseCaches "useCaches"} flag to its
+	 * default value.
 	 * @param con the URLConnection to set the flag on
+	 * @deprecated since now a no-op implementations
 	 */
+	@Deprecated(since = "6.1.1", forRemoval = true)
 	public static void useCachesIfNecessary(URLConnection con) {
-		con.setUseCaches(con.getClass().getSimpleName().startsWith("JNLP"));
 	}
 
 }