- RowMapper is another important concept in Java database programming, especially when working with the Spring Framework’s JDBC template. It is an interface that defines a method for mapping each row of a ResultSet to a corresponding Java object.
- The RowMapper interface is commonly used when you want to convert each row of query results into individual Java objects.
Create a RowMapper:
- You create a custom class that implements the RowMapper interface. This class defines the logic for mapping each row of the ResultSet to a Java object.
Override the mapRow method:
- In your custom RowMapper implementation, you override the mapRow method, which takes a ResultSet and an integer row number as parameters. Inside this method, you write code to extract data from the result set and create a Java object for the current row.
- Like ResultSetExtractor, we can use RowMapper interface to fetch the records from the database using query() method of JdbcTemplate class. In the execute of we need to pass the instance of RowMapper now.
Use the RowMapper with Spring JDBC:
- You can use the RowMapper with Spring’s JDBC template to execute SQL queries. When you execute a query using the template’s query method, you pass in an instance of your custom RowMapper as an argument. Spring handles the database interaction, and your RowMapper is responsible for mapping each row of the result set to Java objects.
import org.springframework.jdbc
.core.JdbcTemplate;
import org.springframework.jdbc
.core.RowMapper;
public class MyRowMapper
implements RowMapper<MyObject> {
@Override
public MyObject mapRow(ResultSet resultSet,
int rowNum) throws SQLException {
MyObject myObject = new MyObject();
// Extract data from the result set
and populate MyObject
myObject.setId(resultSet.getInt("id"));
myObject.setName(resultSet.getString
("name"));
// Add more fields as needed
return myObject;
}
}
public class MyService {
private JdbcTemplate jdbcTemplate;
public MyService
(JdbcTemplate jdbcTemplate) {
this.jdbcTemplate = jdbcTemplate;
}
public List<MyObject> getAllMyObjects() {
String sql = "SELECT * FROM my_table";
return jdbcTemplate.query(sql,
new MyRowMapper());
}
}
- In this example, MyRowMapper is a custom RowMapper implementation that maps each row of the ResultSet to a MyObject instance. The MyService class uses Spring’s JDBC template to execute the query and applies the RowMapper to convert the result set into a list of MyObject instances.
- Using RowMapper with Spring JDBC simplifies the process of mapping database results to Java objects, especially when dealing with multiple rows of data, and provides a clean separation of concerns between database access and data mapping.
