SearchServlet has been compiled by a more recent version of the Java Runtime

"When I go to my compiler I am using compiler compliance level 9." Version 52.0 is Java 8; I assume 53.0 is Java 9. You are attempting to run code compiled for Java 9 on Java 8, which results in the error you are getting. Change your compliance version to Java 8.

IDE: Eclipse Oxygen.

To temporarily correct the problem do the following:

Project menu > Properties > Java Compiler > Compiler compliance level > 1.8

A permanent fix likely involves installing JDK 9.

FYI 1.8 is what Java 8 is called.

Side bar

I recently returned to Java after a foray into C# and installed Eclipse Oxygen onto a clean system that had never had Java installed on it before. This default everything with a brand new install of Eclipse Oxygen yet somehow or other Eclipse can't get its own parameters to match the jdk that's installed. This is the second project I created and the second time I ran into this headache.