Spring Study[12]

There is also a subinterface you can implement that is useful for retrieving multiple objects through a query. Suppose we want a method that retrieves all of our Person objects. To do this we would implement ResultReader. Spring provides an implementation of this interface that does exactly what we need: RowMapperResultReader.

The RowMapper interface is responsible for mapping a ResultSet row to an object.

class PersonRowMapper implements RowMapper {

public Object mapRow(ResultSet rs, int index)

throws SQLException {

Person person = new Person();

person.setId(new Integer(rs.getInt("id")));

person.setFirstName(rs.getString("first_name"));

person.setLastName(rs.getString("last_name"));

return person;

}

}

public List getAllPersons() {

String sql = "select id, first_name, last_name from person";

return jdbcTemplate.query(

sql, new RowMapperResultReader(new PersonRowMapper()));

}

Similarly, to execute a query to find the last name for a particular person id, we would write a method like this:

public String getLastNameForId(Integer id) {

String sql = "select last_name from person where id = ?";

return (String) jdbcTemplate.queryForObject(

sql, new Object[] { id }, String.class);

}

Calling stored procedures:

public void archiveStudentData() {

CallableStatementCallback cb = new CallableStatementCallback() {

public Object doInCallableStatement(CallableStatement cs)

throws SQLException{

cs.execute();

return null;

}

};

jdbcTemplate.execute("{ ARCHIVE_STUDENTS }", cb);

}

Creating operations as objects:

Spring provides a way to actually model database operations as objects. This adds another layer of insulation between your code and straight JDBC.

To create a reusable object for executing inserts or updates, you subclass the SqlUpdate class.

public class InsertPerson extends SqlUpdate {

public InsertPerson(DataSource ds) {

setDataSource(ds);

setSql("insert into person (id, firstName, lastName) " +

"values (?, ?, ?)";

declareParameter(new SqlParameter(Types.NUMERIC));

declareParameter(new SqlParameter(Types.VARCHAR));

declareParameter(new SqlParameter(Types.VARCHAR));

compile();

}

public int insert(Person person) {

Object[] params = new Object[] {

person.getId(),

person.getFirstName(),

person.getLastName()

};

return update(params);

}

}

private InsertPerson insertPerson;

public int insertPerson(Person person) {

return updatePerson.insert(person);

}

Querying the database with a MappingSqlQuery:

To model a query as an object, we subclass the MappingSqlQuery class.

private class PersonByIdQuery extends MappingSqlQuery {

public PersonByIdQuery(DataSource ds) {

super(ds, "select id, first_name, last_name from person " +

"where id = ?");

declareParameter(new SqlParameter("id", Types.INTEGER));

compile();

}

public Object mapRow(ResultSet rs, int rowNumber)

throws SQLException {

Person person = new Person();

person.setId( (Integer) rs.getObject("id"));

person.setFirstName(rs.getString("first_name"));

person.setLastName(rs.getString("last_name"));

return person;

}

}

private PersonByIdQuery personByIdQuery;

…

public Person getPerson(Integer id) {

Object[] params = new Object[] { id };

return (Person) personByIdQuery.execute(params).get(0);

}

Introducing Spring’s ORM framework support:

1.Lazy loading

2.Eager fetching—This is the opposite of lazy loading.

3.Caching.

4.Cascading.