How to process a String with an unknown unit as weighed object

How to process a String with an unknown unit as weighed object

I have to process the data received from a database where all values are
numbers with many different units
for example
12.553 mg
23floz
5 oz
23kg
45 kg
etc
To process these data I have to convert everything as a custom object
Quantity(double amount, String unit)
THE PROBLEM
I don't know how many kinds of units there are in the database, I need a
way that cut the numeric part of the data from the unit and keep these
separately in 2 temp String so after that I process the data I could
istanciate a Quantity object correctly
The values not always contains whitespaces that separe the number from the
unit, therefore solution like
String[] tmp = line.split("\\s");
Quantity(Double.parse(tmp[0], tmp[1]);
Unfortunately doesn't work