You could use the command unzip -l [filename] to list the contents of the jar archive file.

First, you might need to install unzip:
sudo apt install unzip

Example of unzip usage on the file gettext.jar:

username@ubuntu-server:~$ unzip -l /usr/share/java/gettext.jar

Archive:  /usr/share/java/gettext.jar

  Length      Date    Time    Name

---------  ---------- -----   ----

        0  2019-03-06 23:31   META-INF/

       66  2019-03-06 23:31   META-INF/MANIFEST.MF

     5657  2019-03-06 23:31   gnu/gettext/DumpResource.class

      699  2019-03-06 23:31   gnu/gettext/GetURL$1.class

     1579  2019-03-06 23:31   gnu/gettext/GetURL.class

---------                     -------

     8001                     5 files

Alternatively, you could use the Java JDK's jar command to view the contents of a jar file: jar -tf [filename]. (See https://stackoverflow.com/questions/320510/viewing-contents-of-a-jar-file)