You can definitely pack a Java application into a single JAR file and skip the Docker. Java's xenophobia (allergy to linking libraries) is the real root of "write once run everywhere" so often all you need is the Java runtime.
Both are self-contained single files you can give to a completely different organization and expect to run on the first attempt with no complications.
It's just that the latter needs Tomcat (not an issue, realistically) and has to be written as EnterpriseFactoryPatternFactorySingletonAbstractBaseFactorySingletonProvider that makes you feel dead inside just from looking at the documentation; while Golang (and similar newer languages) give you a lot more flexibility and better ergonomics on the developer side.
Factory, FactoryFactory, FactoryFactoryFactory, ...
And like the sibling comment noted, once you're allowed to set up the machine to support easy depolyment (e.g. JRE, Tomcat), a WAR becomes a single file deploy.