- ResultSetExtractor is a concept commonly used in Java database programming, especially when working with the Spring Framework’s JDBC template. It is an interface that defines a method for extracting data from a ResultSet after executing a database query.
- ResultSetExtractor is part of the Spring JDBC framework and is used to convert the raw result set data into Java objects or other data structures.
Create a ResultSetExtractor:
- You create a custom class that implements the ResultSetExtractor interface. This class defines the logic for extracting data from the ResultSet and converting it into the desired Java objects or data structures.
Override the extractData method:
- In your custom ResultSetExtractor implementation, you override the extractData method, which takes a ResultSet as a parameter. Inside this method, you write code to iterate through the result set and extract data to create objects or populate data structures.
- We can easily fetch the records from the database using query() method of JdbcTemplate class where we need to pass the instance of ResultSetExtractor.
Use the ResultSetExtractor with Spring JDBC:
- You can use the ResultSetExtractor 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 ResultSetExtractor as an argument. Spring handles the database interaction, and your extractor is responsible for mapping the result set data to Java objects.
import org.springframework.jdbc
.core.JdbcTemplate;
import org.springframework.jdbc
.core.ResultSetExtractor;
public class MyResultSetExtractor
implements
ResultSetExtractor<MyObject> {
@Override
public MyObject extractData
(ResultSet resultSet)
throws SQLException {
MyObject myObject
= new MyObject();
while (resultSet.next()) {
// Extract data from the result set
and populate MyObject
myObject.setId(resultSet.getInt("id"));
myObject.setName(resultSet.getString
("name"));
}
return myObject;
}
}
public class MyService {
private JdbcTemplate jdbcTemplate;
public MyService
(JdbcTemplate jdbcTemplate) {
this.jdbcTemplate = jdbcTemplate;
}
public MyObject
getMyObjectById(int id) {
String sql = "SELECT *
FROM my_table WHERE id = ?";
return jdbcTemplate.query(sql,
new Object[]{id},
new MyResultSetExtractor());
}
}
- In this example, MyResultSetExtractor is a custom ResultSetExtractor implementation that extracts data from the ResultSet and populates a MyObject instance. The MyService class uses Spring’s JDBC template to execute the query and apply the ResultSetExtractor to retrieve the desired data.
- Using ResultSetExtractor with Spring JDBC simplifies the process of mapping database results to Java objects and provides a clean separation of concerns between database access and data mapping.
