The provided gradlew.bat seems to have an issue with the windows environment variable "JAVA_HOME". In my case it points to "C:\Program Files\Java\jdk1.8.0" and my console correctly prints "java -version". Gradle seems to detect my older Java 7 installation and fails to build. If I manually hack the gradlew.bat to use my JDK 8 it works.
For your interest: There is a similar issue at StackOverflow: http://stackoverflow.com/questions/17841589/gradle-build-with-java-8
And to provide the rest of the details: I am using Windows 7 64 bit & Java 8 build 118.