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Spring - ResultSetExtractor

Last Updated : 08 Oct, 2025
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ResultSetExtractor is an interface used to extract data from a ResultSet object returned by executing an SQL query. It is especially useful when mapping an entire ResultSet (multiple rows or nested data) into a single object or collection.

  • Used when a RowMapper is not sufficient (e.g., custom or hierarchical mapping).
  • Allows manual control over ResultSet iteration and transformation.
  • The JdbcTemplate.query() method accepts a ResultSetExtractor instance.

Method Syntax:

Java 
public T extractData(ResultSet resultSet) throws SQLException, DataAccessException;

query() method syntax:

Java 
public <T> T query(String sql, ResultSetExtractor<T> resultSetExtractor);
  • Java: 21 or later
  • Spring Boot: Version 3.2.0 or higher
  • Database: MySQL
  • Build Tool: Maven

Step-by-Step Implementation

Step 1: Define the Database Schema

Execute the following SQL statements to create and populate the Student table.

CREATE TABLE Student (

id INT PRIMARY KEY AUTO_INCREMENT,

name VARCHAR(45) NOT NULL,

department VARCHAR(45) NOT NULL

);


INSERT INTO Student (name, department)

VALUES ('geek', 'computer science');

Step 2: Add Dependencies

Include the following dependencies in your pom.xml file.

pom.xml:

XML 
<project xmlns="https://maven.apache.org/POM/4.0.0"
         xmlns:xsi="https://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="https://maven.apache.org/POM/4.0.0 https://maven.apache.org/xsd/maven-4.0.0.xsd">

    <modelVersion>4.0.0</modelVersion>
    <groupId>com.example</groupId>
    <artifactId>resultset-extractor-demo</artifactId>
    <version>1.0.0</version>

    <properties>
        <java.version>21</java.version>
        <spring-boot.version>3.2.0</spring-boot.version>
    </properties>

    <dependencies>
        <!-- Spring Boot Starter JDBC -->
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-jdbc</artifactId>
            <version>${spring-boot.version}</version>
        </dependency>

        <!-- MySQL Connector -->
        <dependency>
            <groupId>com.mysql</groupId>
            <artifactId>mysql-connector-j</artifactId>
            <version>8.0.33</version>
            <scope>runtime</scope>
        </dependency>

        <!-- Spring Boot Starter Test -->
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-test</artifactId>
            <version>${spring-boot.version}</version>
            <scope>test</scope>
        </dependency>
    </dependencies>

    <build>
        <plugins>
            <plugin>
                <groupId>org.springframework.boot</groupId>
                <artifactId>spring-boot-maven-plugin</artifactId>
                <version>${spring-boot.version}</version>
            </plugin>
        </plugins>
    </build>
</project>

Step 3: Create a Model Class

Define the model class representing the student entity.

Student.java:

Java 
public record Student(int id, String name, String department) {}

Step 4: Create a DAO Interface

Create a StudentDao interface for database access operations.

Java 
import java.util.List;

public interface StudentDao {
    List<Student> getAllStudents();
}

Step 5: Implement the DAO using ResultSetExtractor

Create the implementation class that uses ResultSetExtractor to map query results.

StudentDaoImpl.java:

Java 
import org.springframework.jdbc.core.JdbcTemplate;
import org.springframework.jdbc.core.ResultSetExtractor;
import org.springframework.stereotype.Repository;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.util.ArrayList;
import java.util.List;

@Repository
public class StudentDaoImpl implements StudentDao {

    private final JdbcTemplate jdbcTemplate;

    public StudentDaoImpl(JdbcTemplate jdbcTemplate) {
        this.jdbcTemplate = jdbcTemplate;
    }

    @Override
    public List<Student> getAllStudents() {
        String sql = "SELECT id, name, department FROM Student";
        return jdbcTemplate.query(sql, new StudentResultSetExtractor());
    }

    private static class StudentResultSetExtractor implements ResultSetExtractor<List<Student>> {
        @Override
        public List<Student> extractData(ResultSet rs) throws SQLException {
            List<Student> students = new ArrayList<>();
            while (rs.next()) {
                int id = rs.getInt("id");
                String name = rs.getString("name");
                String department = rs.getString("department");
                students.add(new Student(id, name, department));
            }
            return students;
        }
    }
}

Step 6: Configure Database Connection

Add the configuration to application.yml.

application.yml:

spring:

datasource:

url: jdbc:mysql://localhost:3306/school_db

username: root

password: pass

driver-class-name: com.mysql.cj.jdbc.Driver

Step 7: Create the Main Application Class

Create a main class to bootstrap the Spring Boot application.

ResultSetExtractorApplication.java:

Java 
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;

@SpringBootApplication
public class ResultSetExtractorApplication {
    public static void main(String[] args) {
        SpringApplication.run(ResultSetExtractorApplication.class, args);
    }
}

Step 8: Write the Test Class

Write a simple integration test to verify data fetching.

StudentDaoTest.java:

Java 
import org.junit.jupiter.api.Test;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.test.context.SpringBootTest;
import java.util.List;
import static org.junit.jupiter.api.Assertions.assertFalse;

@SpringBootTest
public class StudentDaoTest {

    @Autowired
    private StudentDao studentDao;

    @Test
    public void testGetAllStudents() {
        List<Student> students = studentDao.getAllStudents();
        assertFalse(students.isEmpty());
        students.forEach(System.out::println);
    }
}

Step 9: Run the Application

Run the project using:

mvn spring-boot:run

Output

When executed, the console will print the student records retrieved from the database.

Output
Output



A

ankur035
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