When I install JAVA gateway using the official repo from Zabbix, the JAVA gateway doesn't start allthough the init script reports [OK]. When I try to start the gateway manually, I get this error:
Exception in thread "main" java.lang.UnsupportedClassVersionError: com/zabbix/gateway/JavaGateway : Unsupported major.minor version 52.0
at java.lang.ClassLoader.defineClass1(Native Method)
at java.lang.ClassLoader.defineClass(ClassLoader.java:800)
at java.security.SecureClassLoader.defineClass(SecureClassLoader.java:142)
at java.net.URLClassLoader.defineClass(URLClassLoader.java:449)
at java.net.URLClassLoader.access$100(URLClassLoader.java:71)
at java.net.URLClassLoader$1.run(URLClassLoader.java:361)
at java.net.URLClassLoader$1.run(URLClassLoader.java:355)
at java.security.AccessController.doPrivileged(Native Method)
at java.net.URLClassLoader.findClass(URLClassLoader.java:354)
at java.lang.ClassLoader.loadClass(ClassLoader.java:425)
at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:308)
at java.lang.ClassLoader.loadClass(ClassLoader.java:358)
at sun.launcher.LauncherHelper.checkAndLoadMain(LauncherHelper.java:482)

I'm using JAVA 1.7.0.72 (which is automatically installed as a dependency).
The error suggests that the gateway was compiled with JAVA 8.

The workaround is to download the sources, compile the java gateway and place those binaries in /usr/sbin/zabbix_java/. Then it works fine. Installing JAVA 8 won't work because of the dependency in the package.