Where col like 'abc%' with PreparedStatement

The real SQL I want to execute is  SELECT * FROM t WHERE col like 'abc%'; This query

probably can go with IndexScan since it is prefixed with 'abc'.  However I am confused when I want

to use PreparedStatement. 

For example:

       List<Map<String, Object>> imap = jdbcTemplate.queryForList("select * from tm where a like ?",
                new Object[] {"a" + "%"}
                );

The parse tree is sent to postgreSQL is "a like ?",  server knows nothing about if it is prefixed with

something or not, so probably Index Scan can't be selected. So what the user can use the prepared 

Statement and use the IndexScan for the above case? 

Thanks