How to return a java.util.Map from a SQL Object query method

MapReturningSqlObject.java

import java.sql.ResultSet;
import java.sql.SQLException;
import java.util.Collection;
import java.util.HashMap;
import java.util.List;
import java.util.Map;

import org.skife.jdbi.v2.StatementContext;
import org.skife.jdbi.v2.sqlobject.SqlQuery;
import org.skife.jdbi.v2.sqlobject.customizers.RegisterMapper;
import org.skife.jdbi.v2.sqlobject.stringtemplate.UseStringTemplate3StatementLocator;
import org.skife.jdbi.v2.tweak.ResultSetMapper;
import org.skife.jdbi.v2.unstable.BindIn;

@UseStringTemplate3StatementLocator
abstract class MapReturningSqlObject {

    @RegisterMapper(EmailAndAccountNumberResultSetMapper.class)
    @SqlQuery("select email, account_number from customer where email in (<emails>)")
    abstract List<EmailAndAccountNumber> findEmailAndAccountNumbers(@BindIn("emails") Collection<String> emails);

    // this is the public API method that's exposed via @Override-ing a DAO interface;
    // it returns the account number from the customer table for each of the given email addresses
    public Map<String, String> getAccountNumbers(Collection<String> emailAddresses) {
        Map<String, String> map = new HashMap<>();

        for (EmailAndAccountNumber emailAndAccountNumber : findEmailAndAccountNumbers(emailAddresses)) {
            String key = emailAndAccountNumber.email;

            String value = map.containsKey(key) ? "MULTIPLE_ACCOUNTS_FOUND" : emailAndAccountNumber.accountNumber;

            map.put(key, value);
        }
        return map;
    }

    // JDBI *requires* this to be public!
    public static class EmailAndAccountNumberResultSetMapper implements ResultSetMapper<EmailAndAccountNumber> {
        @Override
        public EmailAndAccountNumber map(int index, ResultSet r, StatementContext ctx) throws SQLException {
            return new EmailAndAccountNumber(r.getString("email"), r.getString("account_number"));
        }
    }

    // a helper tuple to get the results out of the SQL Object query method, because we can't register a java.util.Map mapper
    private static class EmailAndAccountNumber {
        final String email;
        final String accountNumber;

        EmailAndAccountNumber(String email, String accountNumber) {
            this.email = email;
            this.accountNumber = accountNumber;
        }
    }
}

As discussed in the JDBI google group thread, here is my best attempt at using a JDBI SQL Query object to fetch a java.util.Map<String, String> from a SQL query.

Github doesn't provide notification emails for comments on gists, so please reply to the thread linked above if you wish to comment, otherwise I might not see it!