Use JarURLConnection caching defaults

In order to prevent leaks of large amounts of non-heap
memory (and potential other efficiency and performance side
effects), this commit updates ResourceUtils#useCachesIfNecessary
to leave the caching flag to its JVM default value for instances
of JarURLConnection.

The previous behavior was 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/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/util/ResourceUtils.java

@@ -18,6 +18,7 @@
 
 import java.io.File;
 import java.io.FileNotFoundException;
+import java.net.JarURLConnection;
 import java.net.MalformedURLException;
 import java.net.URI;
 import java.net.URISyntaxException;
@@ -422,12 +423,14 @@ 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.
+	 * given connection, preferring {@code false} but leaving the flag at
+	 * its JVM default value for jar resources (typically {@code true}).
 	 * @param con the URLConnection to set the flag on
 	 */
 	public static void useCachesIfNecessary(URLConnection con) {
-		con.setUseCaches(con.getClass().getSimpleName().startsWith("JNLP"));
+		if (!(con instanceof JarURLConnection)) {
+			con.setUseCaches(false);
+		}
 	}
 
 }