perf(core): [SDK Overhead Reduction 10] Lazily create reflection JSON serializer

[adinauer]

PR Stack (SDK Overhead Reduction)

• perf(core): SDK Overhead Reduction #5499
• perf(core): [SDK Overhead Reduction 1] Skip java.specification.version lookup on Android #5500
• perf(android): [SDK Overhead Reduction 2] Replace reflective OptionsContainer with direct subclass #5501
• perf(android): [SDK Overhead Reduction 3] Reuse SentryExecutorService for DeviceInfoUtil pre-caching #5502
• perf(android): [SDK Overhead Reduction 4] Use default timezone directly #5587
• perf(core): [SDK Overhead Reduction 5] Replace Calendar with Date in DateUtils #5589
• perf(core): [SDK Overhead Reduction 6] Reduce JsonWriter stack allocation #5591
• perf(core): [SDK Overhead Reduction 7] Lazily allocate Breadcrumb data #5598
• perf(core): [SDK Overhead Reduction 8] Reduce context serialization allocations #5599
• perf(core): [SDK Overhead Reduction 9] Lazily allocate reflection serializer state #5600
• perf(core): [SDK Overhead Reduction 10] Lazily create reflection JSON serializer #5601
• perf(core): [SDK Overhead Reduction 11] Replace ISO8601 timestamp handling #5602
• perf(core): [SDK Overhead Reduction 12] Avoid cloning Date getters #5603
• fix(core): [SDK Overhead Reduction 13] Preserve ISO8601 utility compatibility #5609

---

📜 Description

Lazily creates JsonReflectionObjectSerializer only when unknown-object reflection serialization is used.

Known JSON serialization paths continue to serialize directly without creating the reflection serializer. Unknown-object fallback keeps using the same reflection serializer behavior once needed.

💡 Motivation and Context

Most SDK payloads serialize through explicit JsonSerializable implementations or other directly supported types. Those paths do not need reflection fallback, so eagerly allocating JsonReflectionObjectSerializer for every writer adds unnecessary overhead.

💚 How did you test it?

• ./gradlew :sentry:test --tests io.sentry.JsonObjectSerializerTest
• ./gradlew spotlessApply apiDump
• Re-ran ./gradlew :sentry:test --tests io.sentry.JsonObjectSerializerTest

📝 Checklist

• I added GH Issue ID & Linear ID
• I added tests to verify the changes.
• No new PII added or SDK only sends newly added PII if sendDefaultPII is enabled.
• I updated the docs if needed.
• I updated the wizard if needed.
• Review from the native team if needed.
• No breaking change or entry added to the changelog.
• No breaking change for hybrid SDKs or communicated to hybrid SDKs.

🔮 Next steps

⚠️ Merge this PR using a merge commit (not squash). Only the collection branch is squash-merged into main.

[sentry]

📲 Install Builds

Android

🔗 App Name	App ID	Version	Configuration
SDK Size	io.sentry.tests.size	8.43.1 (1)	release

⚙️ sentry-android Build Distribution Settings

[adinauer]

Cursor review

[adinauer]

@sentry review

[cursor]

✅ Bugbot reviewed your changes and found no new issues!

Comment @cursor review or bugbot run to trigger another review on this PR

^{Reviewed by Cursor Bugbot for commit fd46dbe. Configure here.}

[github-actions]

Performance metrics 🚀

	Plain	With Sentry	Diff
Startup time	369.23 ms	460.06 ms	90.83 ms
Size	0 B	0 B	0 B

Previous results on branch: perf/sdk-overhead-reduction-reflection-serializer

Startup times

Revision	Plain	With Sentry	Diff
28e4d53	383.13 ms	473.56 ms	90.44 ms

App size

Revision	Plain	With Sentry	Diff
28e4d53	0 B	0 B	0 B