I read that java applets aren't allowed to read or write to files fullstop but i can certainly read from a file so I thought my understanding of java applet security might need a little updating ...

All you need to do is compile your Java code into a WASM binary file, and the browser takes care of the rest. Java, WebAssembly and the browser In this tutorial, I will show you how to write logic in ...

How do you deploy a JAR file to Tomcat? Typically you deploy WAR files, not JARs. But if you need to link to a JAR file from a Java web app on Apache Tomcat, here's how to do it.