chore: Readability of CallSiteUtils::toURL

Author: bric3

buildSrc/call-site-instrumentation-plugin/src/main/java/datadog/trace/plugin/csi/util/CallSiteUtils.java

@@ -3,6 +3,7 @@
 import java.io.File;
 import java.net.MalformedURLException;
 import java.net.URL;
+import java.nio.file.Files;
 import java.nio.file.Path;
 import java.util.stream.Collectors;
 import java.util.stream.IntStream;
@@ -48,9 +49,14 @@ public static String repeat(final char value, int count) {
   public static URL toURL(final Path path) {
     try {
       URL url = path.toUri().toURL();
-      // There's a subtle detail where `URLClassLoader` requires directory URLs to end with '/',
-      // otherwise they are assimilated to jar file, and vice versa.
-      if (path.toFile().isDirectory() || !path.toString().endsWith(".jar")) {
+      // URLClassLoader interprets URLs ending with '/' as directories. If the trailing '/' is missing,
+      // a directory URL is treated as a JAR. If the path does yet exist on disk assumes that paths
+      // not ending with ".jar" are directories.
+      boolean shouldAddSlash = Files.exists(path) ?
+          Files.isDirectory(path) :
+          !path.toString().endsWith(".jar");
+
+      if (shouldAddSlash) {
         String urlString = url.toString();
         if (!urlString.endsWith("/")) {
           url = new URL(urlString + "/");