"\Device\NPF_{EC5226CF-3F55-4148-B40E-1FC3F8BB3398} Realtek PCIe GBE Family Controller"
, if you literally mean a String the first character of which is the "D" in "\Device" and the last character of which is the "r" in "Controller", is not a valid WinPcap device name string.
"\Device\NPF_{EC5226CF-3F55-4148-B40E-1FC3F8BB3398}"
would be a valid device name string.
From looking at the Jpcap source, it appears that the findDevice
method does NOT return valid device name strings. It's documented as returning "a string describing the network device"; what it returns is a string containing the device name string, a newline, two blanks, and the device's vendor description string. This has been reported as a Jpcap bug.
I would suggest that you scan the string looking for the first white-space character ("white-space" includes blanks and newlines), and use, as the device name to pass to the open routine, everything up to but not including that white-space character. (If you don't find a white-space character, use the entire string.)