The Spring framework - Making Java Groovy - page 228

public interface RowMapper<T> {
T mapRow(ResultSet rs, int rowNum) throws SQLException
}
Whenyouexecute oneofthe query methods in JdbcTemplate ,Springtakes the Res-
ultSet and feeds each row through an implementation of the RowMapper interface.
The job of the mapRow method is then to convert that row into an instance of the domain
class. The normal Java implementation would be to create an inner class called, say, Ac-
countMapper , whose mapRow method would extract the data from the ResultSet
row and convert it into an Account instance. Providing an instance of the Accoun-
tMapper class to the queryForObject method would then return a single Account .
The same instance can be supplied to the query method, which then returns a collection
of Account s.
This is exactly the type of closure coercion demonstrated in chapter 6 . A variable called
accountMapper is defined and assigned to a closure with the same arguments as the re-
quired mapRow method. The variable is then used in both the findAccountById and
findAllAccounts methods.
There are two uses for Groovy here:
1 . A Groovy class implemented a Java interface, which makes integration easy and
simplifies the code.
2 . Closure coercion eliminated the expected inner class.
Inthe example in the booksource code Ialso included the service class referenced in figure
7.2 . ItusesSpring's @Transactional annotation toensurethat each method operates in
a required transaction. There is nothing inherently Groovy about it, so again I'll just show
an outline of the implementation in the next listing.