Rant "javac: invalid target release: 1.6"

Argh, now I just cannot help myself not to blurt this out. One of the most frustrating small knacks I have come up against lately.

At work, I need to rebuild one customer specific Java web application using JDK 1.6 to match the base product change to target 1.6.

So I login to the build machine, check out that there is JDK 1.6 installed, update the Ant build.xml with new JDK location + target and start the build...

...
compile:
  [echo] ============================================================
  [echo]  Compiling source files
 [javac] Compiling 12 source files to C:\projects\xxx\build\classes
 [javac] javac: invalid target release: 1.6
 [javac] Usage: javac  
 [javac] where possible options include:
 [javac]   -g                         Generate all debugging info
...

WHAT??!! I scratch my head and try editing all the related properties and build script files - trying out all combinations of parameters ...to no avail.

Ok... Google gives me a load of links to discussions like this one on stackoverflow:

Q:
problem in ant build
...
ant source and target to 1.6 en variable path to jdk 1.6

A:
It might be useful for some to know that ant looks at the JAVA_HOME 
variable when deciding which Java version to use

A:
Check the used Java-version with adding following line to your 
target (at the beginning): ...

etc

Well... In our ant script we tell the exact path to the javac executable, so it cannot be that - changing the JAVA_HOME obviously has no effect in this case either.

So to debug the issue I fire up a command prompt and try it manually:

C:\>%JAVA_HOME%\bin\javac -version
javac 1.6.0_21
javac: no source files
Usage: javac  
where possible options include:
...

C:\>%JAVA_HOME%\bin\javac -target 1.6
javac: invalid target release: 1.6
Usage: javac  
where possible options include:
...

BOOM!! There it is - the same error message outside of Ant.

Hmm, now lets try on another JDK 1.6 update:

C:\>set JAVA_HOME=C:\Progra~1\Java\jdk1.6.0_45

C:\>%JAVA_HOME%\bin\javac -version
javac 1.6.0_45

C:\>%JAVA_HOME%\bin\javac -target 1.6
javac: no source files
Usage: javac  
use -help for a list of possible options

...so there have been some broken JDK build(s) out there and the solution is to upgrade the JDK. Phew.

Luckily I get paid for this ;) ...and the Oracle JDK8 for Raspberry Pi (well, "Linux ARM v6/v7 Hard Float ABI") is still pretty awesome :D