your problem seems to be pretty straight forward. Are you looking for exact code to achieve your requirements ?
simple steps could be
1. define your table column as VARCHAR2 type.
2. grab the value of multple checkbox recieved from browser (variable - rval as shown in your post)
3. you can use String concentation operator to append comma between check box values
4. now update that string in table column
for showing that check box data back again,
1. fetch the table column value from database
2. tokenize the string using StringTokenizer using comma as seperator
3. send these individual check box value to jsp page using request or session