fix(filelisting): replace SimpleDateFormat with DateTimeFormatter and Instant

[Avanish Jha (Kingjha13)]

Summary

This PR modernizes date handling in the filelisting sample and fixes several issues.

Changes

• Replace SimpleDateFormat with DateTimeFormatter
• Replace java.util.Date with java.time.Instant
• Fix date pattern from YYYY to yyyy
• Remove usage of request.location() which is no longer available in Ktor 3.x
• Restore CSS rendering by adding the missing unary + in the HTML DSL

Why

• SimpleDateFormat is not thread-safe and can produce incorrect results when shared across concurrent requests.
• DateTimeFormatter is immutable and thread-safe.
• YYYY uses week-based years and can display incorrect years around New Year boundaries.
• Instant is the modern Java time API and integrates cleanly with DateTimeFormatter.
• request.location() causes compilation issues in Ktor 3.x.

Verification

• Built successfully with ./gradlew build
• Verified application startup with ./gradlew run
• Confirmed file listing and info pages render correctly.

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No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: Organization UI

Review profile: CHILL

Plan: Pro

Run ID: 78aa6158-d33d-44e9-aaaf-bbb8479e9244

📥 Commits

Reviewing files that changed from the base of the PR and between c89f051 and 0889322.

📒 Files selected for processing (2)

• filelisting/gradle.properties
• filelisting/src/main/kotlin/io/ktor/samples/filelisting/FileListingApplication.kt

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Walkthrough

File listing sample is updated to use Kotlin 2.3.21 and modernizes date/time handling. The change replaces SimpleDateFormat with DateTimeFormatter and updates the FileInfo data model to use java.time.Instant instead of java.util.Date for file timestamps. The /info HTML output removes request.location() and clarifies CSS formatting.

Changes

File Listing Modernization

Layer / File(s)	Summary
Kotlin compiler version update filelisting/gradle.properties	Kotlin Gradle property updated from 2.3.0 to 2.3.21.
Date/time API modernization filelisting/src/main/kotlin/io/ktor/samples/filelisting/FileListingApplication.kt	Imports updated to use java.time classes (Instant, ZoneId, DateTimeFormatter). FileInfo data class field date changed from java.util.Date to java.time.Instant. File listing logic in listSuspend updated to construct FileInfo with Instant.ofEpochMilli(it.lastModified()) for files and Instant.now() for parent entries. DateTimeFormatter configured with Locale.ENGLISH and ZoneId.systemDefault() replaces SimpleDateFormat.
HTML/CSS presentation updates filelisting/src/main/kotlin/io/ktor/samples/filelisting/FileListingApplication.kt	CSS string in the /info page reformatted with explicit triple-quoted literal and trimIndent(). request.location() output row removed from the info HTML table with a comment noting its removal in Ktor 3.x.

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🎯 2 (Simple) | ⏱️ ~12 minutes

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 0.00% which is insufficient. The required threshold is 80.00%.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title accurately describes the main changes: replacing SimpleDateFormat with DateTimeFormatter and using Instant instead of java.util.Date, which aligns with the file changes and PR objectives.
Description check	✅ Passed	The description is comprehensive and directly related to the changeset, providing clear rationale for each modification and verification steps taken.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

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✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests

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