There are two options I can find; if I understand your question correctly, I think at least one will cover what you are looking for.
If your focus is the data (or a subset thereof) from a single table, use ij
as indicated in the Derby tools documentation (see "Using the bulk import and export procedures"). The data can be extracted from MySQL using intrinsic formatting commands in the required format, which appears to be pretty standard CSV (this would require that you have an appropriate table already existing in your Derby database).
Here's an example from the MySQL forums:
SELECT a,b,a+b INTO OUTFILE '/tmp/result.text'
FIELDS TERMINATED BY ',' OPTIONALLY ENCLOSED BY '"'
LINES TERMINATED BY '\n'
FROM test_table;
If you want to import everything, Apache DdlUtils will allow the transfer of an entire schema from MySQL to Derby. This would not require the repeated table definition in Derby, as it would come across as part of the import/export process with DdlUtils.