ADDITIONAL SYSTEM INFORMATION :
Linux
Property settings:
    file.encoding = UTF-8
    file.separator = /
    java.class.path =
    java.class.version = 69.0
    java.home = /usr/lib/jvm/java-25-openjdk-amd64
    java.io.tmpdir = /tmp
    java.library.path = /usr/java/packages/lib
        /usr/lib/x86_64-linux-gnu/jni
        /lib/x86_64-linux-gnu
        /usr/lib/x86_64-linux-gnu
        /usr/lib/jni
        /lib
        /usr/lib
    java.runtime.name = OpenJDK Runtime Environment
    java.runtime.version = 25.0.2+10-Ubuntu-124.04
    java.specification.name = Java Platform API Specification
    java.specification.vendor = Oracle Corporation
    java.specification.version = 25
    java.vendor = Ubuntu
    java.vendor.url = https://ubuntu.com/
    java.vendor.url.bug = https://bugs.launchpad.net/ubuntu/+source/openjdk-25
    java.version = 25.0.2
    java.version.date = 2026-01-20
    java.vm.compressedOopsMode = Zero based
    java.vm.info = mixed mode, sharing
    java.vm.name = OpenJDK 64-Bit Server VM
    java.vm.specification.name = Java Virtual Machine Specification
    java.vm.specification.vendor = Oracle Corporation
    java.vm.specification.version = 25
    java.vm.vendor = Ubuntu
    java.vm.version = 25.0.2+10-Ubuntu-124.04
    jdk.debug = release
    line.separator = \n
    native.encoding = UTF-8
    os.arch = amd64
    os.name = Linux
    os.version = 6.17.0-14-generic
    path.separator = :
    stderr.encoding = UTF-8
    stdin.encoding = UTF-8
    stdout.encoding = UTF-8
    sun.arch.data.model = 64
    sun.boot.library.path = /usr/lib/jvm/java-25-openjdk-amd64/lib
    sun.cpu.endian = little
    sun.io.unicode.encoding = UnicodeLittle
    sun.java.launcher = SUN_STANDARD
    sun.jnu.encoding = UTF-8
    sun.management.compiler = HotSpot 64-Bit Tiered Compilers
    user.country = DE
    user.dir = /tmp/canonical-path-test
    user.home = /home/<username>
    user.language = de
    user.name = <username>

openjdk version "25.0.2" 2026-01-20
OpenJDK Runtime Environment (build 25.0.2+10-Ubuntu-124.04)
OpenJDK 64-Bit Server VM (build 25.0.2+10-Ubuntu-124.04, mixed mode, sharing)

Windows
Property settings:
    file.encoding = UTF-8
    file.separator = \
    java.class.path =
    java.class.version = 69.0
    java.home = c:\Program Files\Eclipse Adoptium\jdk-25.0.2.10-hotspot
    java.io.tmpdir = C:\Users\bodewig\AppData\Local\Temp\
    java.library.path = c:\Program Files\Eclipse Adoptium\jdk-25.0.2.10-hotspot\bin
        C:\WINDOWS\Sun\Java\bin
        C:\WINDOWS\system32
        C:\WINDOWS
        C:\Program Files\Eclipse Adoptium\jdk-21.0.10.7-hotspot\bin
        C:\Program Files\Eclipse Adoptium\jdk-25.0.2.10-hotspot\bin
        C:\WINDOWS\system32
        C:\WINDOWS
        C:\WINDOWS\System32\Wbem
        C:\WINDOWS\System32\WindowsPowerShell\v1.0\
        C:\Program Files\dotnet\
        C:\WINDOWS\System32\OpenSSH\
        C:\Program Files\PowerShell\7\
        C:\Program Files\Git\cmd
        C:\Users\<username>\.dotnet\tools
        C:\Windows\Microsoft.NET\Framework\v4.0.30319
        C:\Users\<username>\AppData\Local\Microsoft\WindowsApps
        C:\Users\<username>\.dotnet\tools
        C:\xmlunit
        .
    java.runtime.name = OpenJDK Runtime Environment
    java.runtime.version = 25.0.2+10-LTS
    java.specification.name = Java Platform API Specification
    java.specification.vendor = Oracle Corporation
    java.specification.version = 25
    java.vendor = Eclipse Adoptium
    java.vendor.url = https://adoptium.net/
    java.vendor.url.bug = https://github.com/adoptium/adoptium-support/issues
    java.vendor.version = Temurin-25.0.2+10
    java.version = 25.0.2
    java.version.date = 2026-01-20
    java.vm.compressedOopsMode = Zero based
    java.vm.info = mixed mode, sharing
    java.vm.name = OpenJDK 64-Bit Server VM
    java.vm.specification.name = Java Virtual Machine Specification
    java.vm.specification.vendor = Oracle Corporation
    java.vm.specification.version = 25
    java.vm.vendor = Eclipse Adoptium
    java.vm.version = 25.0.2+10-LTS
    jdk.debug = release
    line.separator = \r \n
    native.encoding = Cp1252
    os.arch = amd64
    os.name = Windows 11
    os.version = 10.0
    path.separator = ;
    stderr.encoding = cp437
    stdin.encoding = cp437
    stdout.encoding = cp437
    sun.arch.data.model = 64
    sun.boot.library.path = c:\Program Files\Eclipse Adoptium\jdk-25.0.2.10-hotspot\bin
    sun.cpu.endian = little
    sun.cpu.isalist = amd64
    sun.io.unicode.encoding = UnicodeLittle
    sun.java.launcher = SUN_STANDARD
    sun.jnu.encoding = Cp1252
    sun.management.compiler = HotSpot 64-Bit Tiered Compilers
    sun.os.patch.level =
    user.country = US
    user.dir = C:\temp\canonical-path-test
    user.home = C:\Users\<username>
    user.language = en
    user.name = <username>
    user.script =
    user.variant =

openjdk version "25.0.2" 2026-01-20 LTS
OpenJDK Runtime Environment Temurin-25.0.2+10 (build 25.0.2+10-LTS)
OpenJDK 64-Bit Server VM Temurin-25.0.2+10 (build 25.0.2+10-LTS, mixed mode, sharing)

A DESCRIPTION OF THE PROBLEM :
I'm a developer of Apache Ant and while working on improved symlink/junction support on windows stumbled over a difference of behavior in File.getCanonicalPath between Windows and Linux (and probably other Unices).

Thanks to https://bugs.openjdk.org/browse/JDK-8003887 symlnks and junctions are resolved on Windows since Java 24. This works fine, as long as the file itself exists. If you ask for the canonical path of a non-existent file inside an existing directory symlinks in the file's ancestors are not resolved on Windows. They are resolved if the file exists. Linux resolves symlinks in ancestors in either case.

STEPS TO FOLLOW TO REPRODUCE THE PROBLEM :
On Linux:

mkdir -p /tmp/canonical-path-test/normal
cd /tmp/canonical-path-test
touch normal/exists
ln -s normal symlink
# copy CanonicalPath.java here
/usr/lib/jvm/java-25-openjdk-amd64/bin/javac CanonicalPath.java
# run CanonicalPath for normal/exists, normal/does-not-exist, symlink/exists and symlink/does-not-exist respectively

On Windows
cd \temp
mkdir canonical-path-test
cd canonical-path-test
# copy CanonicalPath.java here
"c:\Program Files\Eclipse Adoptium\jdk-25.0.2.10-hotspot\bin\javac.exe" CanonicalPath.java
mkdir normal
mklink /D symlink c:\temp\canonical-path-test\normal
symbolic link created for symlink <<===>> c:\temp\canonical-path-test\normal
mklink /J junction c:\temp\canonical-path-test\normal
Junction created for junction <<===>> c:\temp\canonical-path-test\normal
echo > normal\exists
# run CanonicalPath for normal/exists, normal/does-not-exist, symlink/exists, symlink/does-not-exist, junction/exists and junction/does-not-exist respectively


---------- BEGIN SOURCE ----------
import java.io.*;

public class CanonicalPath {

    public static void main(String[] args) throws IOException {
        if (args.length != 1) {
            System.err.println("CanonicalPath file");
            System.exit(1);
        }
        System.err.println("getCanonicalPath is " + new File(args[0]).getCanonicalPath());
    }
}

---------- END SOURCE ----------

CUSTOMER SUBMITTED WORKAROUND :
Unfortunately Path#toRealPath does not work at all if the path doesn't exist. The only workaround I came up with was walking up the ancestor tree until I find an existing directory. Invoke getCanonicalPath on that and then resolve the rest of the path relative to this resolved ancestor.