You need 2 tables: KEYS and VALUES where VALUES should have a foreign key column referencing KEYS. Example:
TABLE KEYS:
| ID | KEY |
| 1 | key1|
TABLE VALUES:
| ID | KEY_ID | VALUE |
| 1 | 1 | value1|
| 2 | 1 | value2|
Now to persist a multimap you need to first persist the a key in the KEYS table and then the corresponding values in the VALUES table. Let me know if you need an example of that.
EDIT: See comments
You should use the foreach tags in mybatis. Do a foreach on the keyset or on the entries. Something like this should work:
INSERT INTO table1 (integer1, integer2)
VALUES
<foreach item="item" seperator="," collection="#{entries}">
( #{item.key)},#{item.value})
</foreach>
Where entries should reference the MultiMap.Entries()