I’m occasionally asked what language the application is written in, the answer is Java, not J2EE.
J2EE is actually now called JEE – Java Enterprise Edition. Spider, the authors, do not need to use JEE. JEE includes additional powerful libraries that are not utilised. The software is written in the Java program language. It does require the use of Apache Tomcat which is a Java Application Server – basically a web server that is able to compile and run Java code. Beginning with Java 11, OpenJDK11 is used instead of Java SE. Both are produced by Oracle and both are driven by the same codebase. From Java 11, Oracle started charging for the Standard Edition version, but they still offer a free version via OpenJDK11.