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I'm trying to figure out which environment variable java uses to find/detect the JRE used by C:\ProgramData\Oracle\Java\javapath\java.exe.

As per Oracle's design, the only files I have in the C:\ProgramData\Oracle\Java\javapath\ are

  • java.exe
  • javaw.exe
  • javaws.exe

If I set my JAVA_HOME to empty or to some random folder, running an application with java.exe still works. So I can only assume that it isn't using the JAVA_HOME value. So how does it find the JRE folder? Does it default to something specific? I have no JRE_HOME var set either.

Maciej Los
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Eric B.
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  • Did you look at you PATH environment variable? – OldProgrammer Mar 28 '18 at 17:04
  • @OldProgrammer sure. I have other java paths defined there. But will java.exe use the path env variable to find the necessary libs it requires? I would have expected it to need the JAVA_HOME var - and not expect it to use that PATH var. Normally, I would expect the PATH to be used to find executables. Furthermore, if I clear the PATH var to only have C:\ProgramData\Oracle\Java\javapath\ defined, java still runs. – Eric B. Mar 28 '18 at 17:06
  • I believe beside the path variable the java.exe in system32 used a regedit lookup. This behavior cost me a lot of hours of my life... – 98percentmonkey Nov 18 '18 at 11:31
  • @EricB. In order to run any programs in Windows or Linux, either the file is in your current directory, or you provide the full path to the executable file, or the directory is included in the PATH environment variable. – Clon Nov 18 '21 at 08:04

4 Answers4

27

Regular Directory with File Symlinks inside

If you look at the files in C:\ProgramData\Oracle\Java\javapath\ you will see that they are actually symlinks to a specific java binaries.

2015-11-13  06:11 PM    <SYMLINK>      java.exe [C:\Program Files\Java\jre1.8.0_65\bin\java.exe]
2015-11-13  06:11 PM    <SYMLINK>      javaw.exe [C:\Program Files\Java\jre1.8.0_65\bin\javaw.exe]
2015-11-13  06:11 PM    <SYMLINK>      javaws.exe [C:\Program Files\Java\jre1.8.0_65\bin\javaws.exe]

Directory Junction with regular Files inside

Using the latest (64! bit) install of Java 8 actually prepends onto the system path another location: c:\Program Files (x86)\Common Files\Oracle\Java\javapath. This time, the javapath itself is the junction:

2018-07-21  05:59 PM    <JUNCTION>     javapath [C:\Program Files (x86)\Common Files\Oracle\Java\javapath_target_172906453]
2018-07-21  05:59 PM    <DIR>          javapath_target_172906453

And now, interestingly, the java.exe etc. in the javapath_target_... folder are not symlinks. These files find JRE and JDK versions using this registry location:

[HKEY_LOCAL_MACHINE\SOFTWARE\JavaSoft\Java Runtime Environment]
"CurrentVersion"="1.8"

[HKEY_LOCAL_MACHINE\SOFTWARE\JavaSoft\Java Runtime Environment\1.8]
"JavaHome"="C:\\Program Files\\Java\\jre1.8.0_65"
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Chris Becke
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  • Interestingly I tried changing the version via the registry, and then get `Error: Registry key 'Software\JavaSoft\Java Runtime Environment'\CurrentVersion' has value '11.0.5', but '1.8' is required.` – OrangeDog Nov 11 '19 at 12:43
20

This will give you an idea:

java -verbose | more
access_granted
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    Thanks. It pointed me to the c:\Program Files(x86)\java folder. I'm still not sure I understand why it defaults to there, but at least I know where it is looking now. – Eric B. Mar 29 '18 at 14:28
11

These "new" JDK 8 / 64-bit behavior is so obfuscated, I could not guess why my application would not start, because I had the JDK (with the private JRE) and every path variable setup, still no start. After some time I installed JRE8 alone and it worked. Firstly the regedit - keys are only written by the public JRE.... Ok.

Then I wanted to know which Runtime the app used, I renamed all java* .exe, yet it still worked64-bitI renamed all-new regedit keys. It still worked...

End of story: with Windows 64 the regedit keys are in HKEY_LOCAL_MACHINE\SOFTWARE\JavaSoft (32bit) and

HKEY_LOCAL_MACHINE\SOFTWARE\WOW6432Node\JavaSoft (64bit)

and my app worked because 

HKEY_LOCAL_MACHINE\SOFTWARE\WOW6432Node\JavaSoft\Java Runtime Environment\1.8\RuntimeLib\

pointed to jvm.dll which revered a symlink. I need a beer, I want another Job :-)

Here is a nice link, which explains the Regedit-Keys and the different "discovery methods" which Java uses to find the newest installed version:

http://mindprod.com/jgloss/registry.html

Still the SYSLink - Change with JDK8 seems to be an undocumented change which was introduced before JRE8u171.

My sysLink Path was C:\Program Files (x86)\Common Files\Oracle\Java with was actually a Junction to a subdirectory. And the JDK8 installer copies the java*.exe files into Windows\System32\ btw.

More Infos:

Sorry for my rant, I'm so frustrated right now. I hope it helps somebody else.

98percentmonkey
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6

Try java -verbose with findstr

Example:

C:\>java -verbose 2>nul | findstr /I opened
[Opened C:\Program Files\Java\jre1.8.0_201\lib\rt.jar]

Try reg query with /s

Example:

C:\>reg query "HKEY_LOCAL_MACHINE\SOFTWARE\JavaSoft\Java Runtime Environment" /s

HKEY_LOCAL_MACHINE\SOFTWARE\JavaSoft\Java Runtime Environment
    CurrentVersion    REG_SZ    1.8
    BrowserJavaVersion    REG_SZ    11.201.2

HKEY_LOCAL_MACHINE\SOFTWARE\JavaSoft\Java Runtime Environment\1.8
    RuntimeLib    REG_SZ    C:\Program Files\Java\jre1.8.0_201\bin\server\jvm.dll
    JavaHome    REG_SZ    C:\Program Files\Java\jre1.8.0_201
    MicroVersion    REG_SZ    0

HKEY_LOCAL_MACHINE\SOFTWARE\JavaSoft\Java Runtime Environment\1.8.0_201
    JavaHome    REG_SZ    C:\Program Files\Java\jre1.8.0_201
    MicroVersion    REG_SZ    0
    RuntimeLib    REG_SZ    C:\Program Files\Java\jre1.8.0_201\bin\server\jvm.dll

HKEY_LOCAL_MACHINE\SOFTWARE\JavaSoft\Java Runtime Environment\1.8.0_201\MSI
    INSTALLDIR    REG_SZ    C:\Program Files\Java\jre1.8.0_201\
    JU    REG_SZ
    OEMUPDATE    REG_SZ
    FROMVERSION    REG_SZ    NA
    FROMVERSIONFULL    REG_SZ
    PRODUCTVERSION    REG_SZ    8.0.2010.9
    EULA    REG_SZ
    JAVAUPDATE    REG_SZ    1
    AUTOUPDATECHECK    REG_SZ    1
    AUTOUPDATEDELAY    REG_SZ
    FullVersion    REG_SZ    1.8.0_201-b09


C:\>

Try Get-Command java

Note: If you just care about the version number, then you might want to try PowerShell's Get-Command:

PS C:\> Get-Command java | ft -AutoSize

CommandType  Name      Version    Source
-----------  ----      -------    ------
Application  java.exe  8.0.201.9  C:\Program Files (x86)\Common
Files\Oracle\Java\javapath\java.exe
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