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Quickly retrieve available Java JVM on a workstation (Windows)Tag(s): Environment


Using regedit
Use regedit utility to query the Windows registry, the result is written into a file. 
start /w regedit /e jre.txt
   "HKEY_LOCAL_MACHINE\SOFTWARE\JavaSoft\Java Runtime Environment"

The content of jre.txt on my machine : 

Windows Registry Editor Version 5.00

[HKEY_LOCAL_MACHINE\SOFTWARE\JavaSoft\Java Runtime Environment]
"CurrentVersion"="1.5"

[HKEY_LOCAL_MACHINE\SOFTWARE\JavaSoft\Java Runtime Environment\1.4]
"JavaHome"="C:\\Program Files\\Java\\j2re1.4.1_02"
"RuntimeLib"="C:\\Program Files\\Java\\j2re1.4.1_02\\bin\\client\\jvm.dll"
"MicroVersion"="1"

[HKEY_LOCAL_MACHINE\SOFTWARE\JavaSoft\Java Runtime Environment\1.4.1_02]
"JavaHome"="C:\\Program Files\\Java\\j2re1.4.1_02"
"MicroVersion"="1"
"RuntimeLib"="C:\\Program Files\\Java\\j2re1.4.1_02\\bin\\client\\jvm.dll"

[HKEY_LOCAL_MACHINE\SOFTWARE\JavaSoft\Java Runtime Environment\1.5]
"JavaHome"="C:\\Program Files\\Java\\jre1.5.0"
"RuntimeLib"="C:\\Program Files\\Java\\jre1.5.0\\bin\\client\\jvm.dll"
"MicroVersion"="0"

[HKEY_LOCAL_MACHINE\SOFTWARE\JavaSoft\Java Runtime Environment\1.5.0]
"JavaHome"="C:\\Program Files\\Java\\jre1.5.0"
"MicroVersion"="0"
"RuntimeLib"="C:\\Program Files\\Java\\jre1.5.0\\bin\\client\\jvm.dll"
Using a CMD file
A CMD file for Windows to display the default JRE used : 
@echo off
::Find the current (most recent) Java version
start /w regedit /e reg1.txt "HKEY_LOCAL_MACHINE\SOFTWARE\JavaSoft\Java Runtime Environment"
type reg1.txt | find "CurrentVersion" > reg2.txt
if errorlevel 1 goto ERROR
for /f "tokens=2 delims==" %%x in (reg2.txt) do set JavaTemp=%%~x
if errorlevel 1 goto ERROR
echo Java Version = %JavaTemp%
del reg1.txt
del reg2.txt

::Get the home directory of the most recent Java
start /w regedit /e reg1.txt "HKEY_LOCAL_MACHINE\SOFTWARE\JavaSoft\Java Runtime Environment\%JavaTemp%"
type reg1.txt | find "JavaHome" > reg2.txt
if errorlevel 1 goto ERROR
for /f "tokens=2 delims==" %%x in (reg2.txt) do set JavaTemp=%%~x
if errorlevel 1 goto ERROR
echo Java home path (per registry) = %JavaTemp%
del reg1.txt
del reg2.txt

pause
Output example : 
C:\temp>findjava.cmd
Java Version = 1.6
Java home path (per registry) = C:\\applications\\dev\\jre6

Note :
The above script returns the default JVM if the PATH variable does not override it!
Oracle client installation is famous to force an outdated Java at the beginning of the PATH. This one-liner displays the java.exe (if any) found in the PATH : 

c:\> for %i in (java.exe) do @echo.   %~$PATH:i
   C:\WINDOWS\system32\java.exe
The java.exe in the system32 relies on the CurrentVersion registry setting to determine which registry key to use to look up the location of the Java RE.