Sorry I'm new to the forums, never really had a problem until now. Which log file do you need? Is it one of the FML-Client-log files or the FTB one?
The FTB log reports the following:
[22:42:29] [DEBUG] MainHelpers.printInfo:40: System's default JVM: (This is not always used to launch MC)
[22:33:51] [DEBUG] MainHelpers.printInfo:41: Java version: 1.8.0_121
[22:33:51] [DEBUG] MainHelpers.printInfo:42: Java vendor: Oracle Corporation
[22:33:51] [DEBUG] MainHelpers.printInfo:43: Java home: C:\Program Files\Java\jre1.8.0_121
[22:33:51] [DEBUG] MainHelpers.printInfo:44: Java specification: Java Virtual Machine Specification version: 1.8 by Oracle Corporation
[22:33:51] [DEBUG] MainHelpers.printInfo:46: Java vm: Java HotSpot(TM) 64-Bit Server VM version: 25.121-b13 by Oracle Corporation
...
[22:33:51] [INFO] JavaFinder.parseJavaVersion:175: The FTB Launcher has found the following Java versions installed:
[22:33:51] [INFO] JavaFinder.parseJavaVersion:177: Java Version: 1.8.0_121 sorted as: 1.8.0_121 64 Bit Java at : C:\Program Files\Java\jre1.8.0_121\bin\java.exe
[22:33:51] [INFO] JavaFinder.parseJavaVersion:177: Java Version: 1.8.0_121 sorted as: 1.8.0_121 64 Bit Java at : C:\Program Files\Java\jre1.8.0_121\bin\java.exe
[22:33:51] [INFO] JavaFinder.parseJavaVersion:204: Preferred: Java Version: 1.8.0_121 sorted as: 1.8.0_121 64 Bit Java at : C:\Program Files\Java\jre1.8.0_121\bin\java.exe
When Default is selected in the launcher's advanced options it boots up javaw.exe. When I change it to one of the 1.8.0_121 versions it boots up java.exe. In both cases the FML client log reports:
[21:52:31] [main/INFO] [FML/]: Java is Java HotSpot(TM) 64-Bit Server VM, version 1.8.0_121, running on Windows 7:amd64:6.1, installed at C:\Program Files\Java\jre1.8.0_121