Windows does not know what to do with a file with a .jar extension by default. You will need to pass the path to the .jar into the JRE using a fully qualified path to the runtime (e.g. C:\Program Files\...etc...\java.exe) in your Execute Process Task and making the reference to the .jar file a command line argument.
There are no special teachers of virtue, because virtue is taught by the whole community. --Plato