I just found the following link, which describes the whole procedure in order to debug a Java jar remotely.
Debug Java applications remotely with Eclipse
The main parts are:
Target VM acts as debug server
java -Xdebug -Xrunjdwp:transport=dt_socket,server=y,address="8000" -jar
Target VM acts as debug client
java -Xdebug -Xrunjdwp:transport=dt_socket,address=127.0.0.1:8000,suspend=y
Based on how you run the target vm, client or server, you have to configure Eclipse differently.
Eclipse configuration if you start the target vm as client
Eclipse configuration if you start the target vm as server
The article gives also a gently introduction into the topic.