Disconnect HttpURLConnection in AbstractFileResolvingResource

[SebTardif]

Summary

Ensure HttpURLConnection instances are always disconnected in AbstractFileResolvingResource's exists(), checkReadable(), contentLength(), and lastModified() methods.

Problem

These four methods open URLConnection instances via url.openConnection() that are never disconnected on most code paths. This leaks underlying sockets when resources are accessed over HTTP.

Additionally, on the 405 (Method Not Allowed) retry paths, the original connection reference is silently overwritten when a new connection is opened — the original connection is leaked since no reference to it remains.

This class is the base for ClassPathResource, UrlResource, and all classpath/URL resources in Spring, so any code checking resource existence, readability, content length, or last-modified over HTTP is affected.

Fix

• Wrap HTTP connection usage in try-finally blocks to ensure disconnect() is always called regardless of which code path is taken
• Explicitly disconnect the original connection before opening a retry connection on 405 paths
• Set httpCon = null when a retry yields a non-HTTP connection to avoid disconnecting a stale reference

No behavioral changes — only resource cleanup is added.