I followed the Java 7u21 guide as well. However I found the MSI Product code to be different for Java 8u31.
For Java 7u21 (from the guide)
Msi Product code for x86 is: 26A24AE4-039D-4CA4-87B4-2F83217021FF
Msi Product code for x64 is: 26A24AE4-039D-4CA4-87B4-2F86417021FF
For Java 8u31 I found the following uninstall key in the registry.
MsiExec.exe /I{26A24AE4-039D-4CA4-87B4-2F83218031F0}
MsiExec.exe /I{26A24AE4-039D-4CA4-87B4-2F86418031F0}
So I used the following when creating my Java 8u31 package in WPP and followed the 7u21 guide with these edits:
Msi Product code for x86 is: 26A24AE4-039D-4CA4-87B4-2F83218031F0
Msi Product code for x64 is: 26A24AE4-039D-4CA4-87B4-2F86418031F0
For Java 7u21 (from the guide)
Msi Product code for x86 is: 26A24AE4-039D-4CA4-87B4-2F83217021FF
Msi Product code for x64 is: 26A24AE4-039D-4CA4-87B4-2F86417021FF
For Java 8u31 I found the following uninstall key in the registry.
MsiExec.exe /I{26A24AE4-039D-4CA4-87B4-2F83218031F0}
MsiExec.exe /I{26A24AE4-039D-4CA4-87B4-2F86418031F0}
So I used the following when creating my Java 8u31 package in WPP and followed the 7u21 guide with these edits:
Msi Product code for x86 is: 26A24AE4-039D-4CA4-87B4-2F83218031F0
Msi Product code for x64 is: 26A24AE4-039D-4CA4-87B4-2F86418031F0