org.springframework.util.ResourceUtils#toRelativeURL drops custom URLStreamHandler

[ljcvok]

This relates to #33199

Due to the custom encryption of JARs we have a custom java.net.URLStreamHandler on URL instance.
In recent versions (from 6.1.x) the reimplemented method org.springframework.util.ResourceUtils#toRelativeURL fails to retain the original URLStreamHandler on the root URL instance. Instead, it uses only the string part of the URL and creates a new one.

6.1.x:
toURL(StringUtils.applyRelativePath(root.toString(), relativePath));

vs
6.0.x:
new URL(root, relativePath);

I propose similar approach as was the fix for #33199

if (ResourceUtils.toURL(root.toString()).equals(root)) {
  // Plain URL with default URLStreamHandler -> replace with cleaned path.
  return toURL(StringUtils.applyRelativePath(root.toString(), relativePath));;
} else {
  // Retain original URL instance, potentially including custom URLStreamHandler.
  return new URL(root, relativePath);
}

[fendo8888]

I used xjar here to upgrade to spring 3.x and encountered this problem：core-lib/xjar#133

[fendo8888]

Seemingly not in xjar,ResourceUtils.toURL(root.tostring ()).equals(root) is always true,How to make ResourceUtils.toURL(root.tostring ()).equals(root) return false and call return new URL(root, relativePath)

[jhoeller]

It looks like depending on the URLStreamHandler implementation underneath, the ResourceUtils.toURL(root.toString ()).equals(root) check may indeed mis-identify the URL as equal even if it does not have the same handler associated. This may also apply to the fix in #33199, as far as I can see.

@ljcvok what specific condition causes that equals check to return false in your scenario? Is it within your custom handler?