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Multiple Java versions on Windows: pin JAVA_HOME per service

Verified 2 min read

Keep JDK 17 and 21 side by side, pin JAVA_HOME in each Tomcat/service wrapper, and stop relying on a machine-wide PATH switch.

Tested onStandard / Datacenter · Build 26100.33650 · x64
E1
Build
26100.33650
Edition
Standard / Datacenter
Architecture
x64
Support
Documentation (E1)
Evidence
E1Official documentation
Verified
2026-10-29
Page type
Method

The short answer

Section titled “The short answer”

Do not switch Java globally with setx JAVA_HOME and hope every service picks it up. Pin the JDK per service:

C:\Java\jdk-17\
C:\Java\jdk-21\
C:\apps\tomcat-a\setenv.bat   -> JAVA_HOME=C:\Java\jdk-17
C:\apps\tomcat-b\setenv.bat   -> JAVA_HOME=C:\Java\jdk-21

PATH is for your interactive shell. A Windows service gets its environment when it starts; changing the machine PATH does not retarget a running service.

Install side by side

Section titled “Install side by side”
  1. Download Temurin/Microsoft OpenJDK zips for each LTS.
  2. Extract to versioned directories, not C:\Program Files\Java\latest.
  3. Do not add either bin to the machine PATH unless you need a default CLI.
  4. Verify each:
Terminal window
& C:\Java\jdk-17\bin\java.exe -version
& C:\Java\jdk-21\bin\java.exe -version

Keep the full path in scripts; it is the only unambiguous selector.

Tomcat per instance

Section titled “Tomcat per instance”

Tomcat reads JAVA_HOME (or JRE_HOME) at startup. In each instance:

Terminal window
REM C:\apps\tomcat-a\bin\setenv.bat
set "JAVA_HOME=C:\Java\jdk-17"
set "CATALINA_BASE=C:\apps\tomcat-a"
Terminal window
REM C:\apps\tomcat-b\bin\setenv.bat
set "JAVA_HOME=C:\Java\jdk-21"
set "CATALINA_BASE=C:\apps\tomcat-b"

setenv.bat is per instance and survives upgrades better than editing catalina.bat. Keep CATALINA_HOME as the shared Tomcat install if you run multiple instances from one binary; keep CATALINA_BASE per instance (config, logs, webapps).

Windows service

Section titled “Windows service”

If Tomcat runs as a service, the service wrapper must capture the right environment. With the Tomcat service manager:

Terminal window
tomcat10w.exe //ES//TomcatA

Set the Java tab / JVM path to the versioned jre/jdk, or use a wrapper that reads setenv.bat. After changing, restart the service and verify the actual process:

Terminal window
Get-CimInstance Win32_Process -Filter "Name='java.exe'" |
  Select-Object ProcessId, CommandLine

The command line should show the expected JDK path.

Verify the app, not just java -version

Section titled “Verify the app, not just java -version”
Terminal window
Invoke-WebRequest http://localhost:8080/ -UseBasicParsing | Select-Object StatusCode
Get-Content C:\apps\tomcat-a\logs\catalina.*.log -Tail 50

A Tomcat started with the wrong JDK may still boot, then fail on a class file version, TLS provider or GC option. Check the log’s “Java Home”/JVM line.

Upgrade path

Section titled “Upgrade path”
  1. Add the new JDK beside the old.
  2. Test one instance with setenv.bat.
  3. Run the app’s test suite and check TLS/keystore compatibility.
  4. Move instances one at a time.
  5. Remove the old JDK after rollback is no longer needed.

Lab boundary

Section titled “Lab boundary”

E1. The lab did not install a JDK or Tomcat; the commands are the per-service pattern to validate on Server 2025.

Sources