EsotericSoftware/kryo

JDK 25 compatibility

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#1246 opened on Dec 24, 2025

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bughelp wantedkryo 6

Description

Describe the bug JDK 25 reports warnings:

WARNING: A terminally deprecated method in sun.misc.Unsafe has been called 2025-12-23T20:48:33.210463889Z WARNING: sun.misc.Unsafe::arrayBaseOffset has been called by com.esotericsoftware.kryo.unsafe.UnsafeUtil (file:/application/BOOT-INF/lib/kryo-5.6.2.jar) 2025-12-23T20:48:33.210466222Z WARNING: Please consider reporting this to the maintainers of class com.esotericsoftware.kryo.unsafe.UnsafeUtil 2025-12-23T20:48:33.210467514Z WARNING: sun.misc.Unsafe::arrayBaseOffset will be removed in a future release

To Reproduce

        Kryo5Codec cc = new Kryo5Codec();
        cc.getValueEncoder().encode("123123");

Environment:

  • OS: Any
  • JDK Version: 25
  • Kryo Version: 5.6.2

Additional context Redisson lib

Contributor guide

Tech stack
java
Domain
backend
Issue type
bug
DifficultyEstimated implementation difficulty for a new contributor, from 1 for very small changes to 5 for expert-level work.
2
Estimated timeA rough time range for an experienced contributor to investigate, implement, test, and prepare a pull request.
1-3 hours
Activity statusHow available the issue appears right now: fresh, active, stale, blocked, or waiting on maintainer input.
fresh
ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.
clear
Prerequisites
JavaKryo libraryUnsafe API
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
60
Research direction
The issue is about deprecated sun.misc.Unsafe::arrayBaseOffset in JDK 25. The warning is triggered in com.esotericsoftware.kryo.unsafe.UnsafeUtil. Find the exact line where arrayBaseOffset is called and replace it with the recommended replacement using MethodHandles or VarHandle, as per JDK 25 documentation. Ensure backward compatibility with older JDK versions by using conditional code or reflection. Check the Kryo source code for other Unsafe methods that may need similar updates.