As of Grouper 2.2.2 the Provisioning Services Provider (PSP) is not compatible with Java 8 and we recommend using Java 7 with Grouper. You may choose to use either Oracle Java 7 or OpenJDK 7.
As a concrete example, on a Debian 7 system one may do
apt-get install openjdk-7-jdk update-alternatives --config java
and then run
java -version
to verify that the default Java is the correct version. You should see something like this:
java version "1.7.0_95" OpenJDK Runtime Environment (IcedTea 2.6.4) (7u95-2.6.4-1~deb7u1) OpenJDK 64-Bit Server VM (build 24.95-b01, mixed mode)
Hint: If you use OpenJDK 7 be sure that OpenJDK 6 is not also installed on the system. The default startup script for Tomcat 6 may find OpenJDK 6 first if it is installed at the same time as OpenJDK 7.