How to work exactly with Spring RowMapper interface?

Question

I am studying Core Spring certification, and I have some doubts about how Spring handles JDBC requests:

Therefore, I know that I can receive data from my database tables in various ways, depending on the type of data that I expect to receive:

1) A query for a simple type (like int, long or String): I use the queryForObject () method for the jdbcTemplate strong> class, something like this:

String sql = "SELECT count(*) FROM T_REWARD";
int rowsNumber = jdbcTemplate.queryForObject(sql, Integer.class);

So, to get a simple object as an int value, I use the queryForObject () method , passing it the sql stattment and the type of object that I expect to receive in the output from the method.

Well, that’s pretty simple, and I think that everything is in order.

2) A query for the entire row of the table placed in the Map object : so if I do not need a single value (which may be in one column of a specific row in the table or something like a preliminary example). I can use the queryForMap (..) and queryForList () methods as follows:

2.1) queryForMap () : I use it if I expect a single row placed in a single map object , where each column value is displayed in my map, something like:

String sql = "select * from T_REWARD where CONFIRMATION_NUMBER = ?";
Map<String, Object> values = jdbcTemplate.queryForMap(sql,confirmation.getConfirmationNumber());

2.2) queryForList(): , , . Map, Map . - :

String sql = "select * from PERSON";
return jdbcTemplate.queryForList(sql);

, .

ResultSet JdbcTemplate, .

, JdbcTemplate . ?

, Spring RowMapper ResultSet :

public interface RowMapper<T> {
    T mapRow(ResultSet rs, int rowNum)
    throws SQLException;
}

compoese , RestaurandRowMapper queryForObject():

public Restaurant findByMerchantNumber(String merchantNumber) {
    String sql = "select MERCHANT_NUMBER, NAME, BENEFIT_PERCENTAGE, BENEFIT_AVAILABILITY_POLICY from T_RESTAURANT where MERCHANT_NUMBER = ?";

    return jdbcTemplate.queryForObject(sql, new RestaurantRowMapper(), merchantNumber);

:

class RestaurantRowMapper implements RowMapper<Restaurant> {
    public Restaurant mapRow(ResultSet rs, int i) throws SQLException {
        return mapRestaurant(rs);
    }
}

:

private Restaurant mapRestaurant(ResultSet rs) throws SQLException {
    // get the row column data
    String name = rs.getString("NAME");
    String number = rs.getString("MERCHANT_NUMBER");
    Percentage benefitPercentage = Percentage.valueOf(rs.getString("BENEFIT_PERCENTAGE"));
    // map to the object
    Restaurant restaurant = new Restaurant(number, name);
    restaurant.setBenefitPercentage(benefitPercentage);
    restaurant.setBenefitAvailabilityPolicy(mapBenefitAvailabilityPolicy(rs));
    return restaurant;
}

, , , .

: , queryForObject(), , , , (, Interger Long).

, (, Restaurant, Restaurand), , ( "" ), :

return jdbcTemplate.queryForObject(sql, new RestaurantRowMapper(), merchantNumber);

mapRow(),

class RestaurantRowMapper implements RowMapper<Restaurant> {
    public Restaurant mapRow(ResultSet rs, int i) throws SQLException {
        return mapRestaurant(rs);
    }
}

, , Spring mapRow(), Restaurand, queryForObject() - . , .

? , ?

Answer 1

queryForObject :

public <T> T queryForObject(String sql, RowMapper<T> rowMapper, Object... args) throws DataAccessException {
    List<T> results = query(sql, args, new RowMapperResultSetExtractor<T>(rowMapper, 1));
    return DataAccessUtils.requiredSingleResult(results);
}

queryForObject query JdbcTemplate. query :

public <T> T query(
        PreparedStatementCreator psc, final PreparedStatementSetter pss, final ResultSetExtractor<T> rse)
        throws DataAccessException;

, a ResultSetExtractor<T> query Spring RowMapper<T> new RowMapperResultSetExtractor<T>(rowMapper, 1). RowMapperResultSetExtractor - , . , :

public List<T> extractData(ResultSet rs) throws SQLException {
    List<T> results = (this.rowsExpected > 0 ? new ArrayList<T>(this.rowsExpected) : new ArrayList<T>());
    int rowNum = 0;
    while (rs.next()) {
        results.add(this.rowMapper.mapRow(rs, rowNum++));
    }
    return results;
}

, RowMapper - , . , , RowMapper , Restaurant - . , , , , Restaurant.

        return DataAccessUtils.requiredSingleResult(results);

, : JdbcTempalte ( ). , (RowMapper), JdbcTemplate ( , ..). RowMapper POJO (Restaurant), List. queryForObject List . RowMapper, Restaurant.

Answer 2

jdbcTemplate.queryForObject,

public YourPojo getDatabaseDetails(int masterId) {

    sql = "Select * FROM <table_name> where ID=?";
    YourPojo pojo = (YourPojo) jdbcTemplate.queryForObject(sql,
            new Object[] { masterId }, new RowMapper<YourPojo>() {
                @Override
                public <YourPojo> mapRow(ResultSet rs, int rowNum)
                        throws SQLException {
                    YourPojo pojo2 = new YourPojo();
                    pojo2.setAccountId(rs.getString("AccountId"));
                    pojo2.setAccountName(rs.getString("AccountName"));
                    pojo2.setAccountCRN(rs.getString("AccountCRN"));
                    pojo2.setAccountStatus(rs.getString("AccountStatus"));
                    return pojo2;
                }
            });
    return pojo;
}