Hi,
The error message "Unsupported major.minor version 52.0" means the UDF jar file was compile on a version of Java that is different to the one used for HS2.
If you run below command:
javap -verbose com/udf/StringSplitter.class | grep "major"
What is the number returned?
Below are the major version number for different version of Java:
Java 5 uses major version 49
Java 6 uses major version 50
Java 7 uses major version 51
Java 8 uses major version 52
Java 9 uses major version 53
So you need to compile using the Java that has the same version that HS2 runs under.
Hope above helps.