Found it myself:

org.firebirdsql.FBResultSetMetaData.getColumnType(int column):

Look at the blob "case" (line 397)

case GDS.SQL_BLOB:
if (sqlsubtype == 2)
return Types.LONGVARCHAR;
else
return Types.LONGVARBINARY;


Now, I don't know if subtype BLR (=2) is a LONGVARCHAR, but I'm pretty
sure that TEXT(=1) is. So the lines above should look like

if(sqlsubtype==1 | sqlsubtype==2)
return Types.LONGVARCHAR;
else
return Types.LONGVARBINARY;

Am I right? Am I a fool?

Ciao
Luca