If you have the Java Runtime Environment installed, and the JAR file is executable, it should open with a double-click. Sometimes, you might see a pop-up to choose which app to run the file.

Each installation of the Java Development Kit (JDK) includes a JAR utility (named jar.sh on Unix and jar.exe on Windows) that provides a variety of helpful functions for working with JAR files, ...

Starting in April, Oracle will treat JAR files signed with the MD5 hashing algorithm as if they were unsigned, which means modern releases of the Java Runtime ... set up custom Deployment Rule ...