Spring Boot RowMapper

last modified July 28, 2023

In this article we show how to map rows of ResultSet to data carriers. We use Java record as a data carrier.

Spring Boot is a popular application framework for creating enterprise application in Java, Kotlin, or Groovy.

Java record

Java record is a restricted form of a class. Java records eliminate a lot of boilerplate code, including constructor, getters, toString, hashCode and equals methods. They are immutable. Their purpose is to be simple data carriers.

We can use DataClassRowMapper for a seamless integration with Java records. See the Spring BootDataClassRowMapper tutorial.

Spring Boot RowMapper example

The following application uses a RowMapper to map a result set row to a City record.

build.gradle … src ├── main │ ├── java │ │ └── com │ │ └── zetcode │ │ ├── Application.java │ │ ├── mapper │ │ │ └── CityMapper.java │ │ ├── model │ │ │ └── City.java │ │ ├── MyRunner.java │ │ └── service │ │ ├── CityService.java │ │ └── ICityService.java │ └── resources │ ├── application.properties │ ├── data-h2.sql │ └── schema-h2.sql └── test ├── java └── resources

This is the project structure of the Spring Boot application.

build.gradle

plugins { id ‘org.springframework.boot’ version ‘3.1.1’ id ‘io.spring.dependency-management’ version ‘1.1.0’ id ‘java’ }

group = ‘com.zetcode’ version = ‘0.0.1-SNAPSHOT’ sourceCompatibility = ‘17’

repositories { mavenCentral() }

dependencies { implementation ‘org.springframework.boot:spring-boot-starter-jdbc’ runtimeOnly ‘com.h2database:h2’ }

This is the Gradle build file. The RowMapper resides in spring-boot-starter-jdbc.

resources/application.properties

spring.main.banner-mode=off spring.sql.init.platform=h2 spring.datasource.driverClassName=org.h2.Driver spring.datasource.url=jdbc:h2:mem:testdb

In the application.properties, we turn off the Spring Boot banner and set up the H2 datasource.

resources/schema-h2.sql

CREATE TABLE cities(id BIGINT PRIMARY KEY AUTO_INCREMENT, name VARCHAR(255), population BIGINT);

This SQL script creates the cities table.

resources/data-h2.sql

INSERT INTO cities(name, population) VALUES(‘Bratislava’, 432000); INSERT INTO cities(name, population) VALUES(‘Budapest’, 1759000); INSERT INTO cities(name, population) VALUES(‘Prague’, 1280000); INSERT INTO cities(name, population) VALUES(‘Warsaw’, 1748000); INSERT INTO cities(name, population) VALUES(‘Los Angeles’, 3971000); INSERT INTO cities(name, population) VALUES(‘New York’, 8550000); INSERT INTO cities(name, population) VALUES(‘Edinburgh’, 464000); INSERT INTO cities(name, population) VALUES(‘Berlin’, 3671000);

This SQL script fills the table with data.

com/zetcode/model/City.java

package com.zetcode.model;

public record City(Long id, String name, Integer population) {}

We have a City record. Most of the boilderplate for a typical Java model class is removed.

com/zetcode/mapper/CityMapper.java

package com.zetcode.mapper;

import com.zetcode.model.City; import org.springframework.jdbc.core.RowMapper;

import java.sql.ResultSet; import java.sql.SQLException;

public class CityMapper implements RowMapper<City> {

@Override
public City mapRow(ResultSet rs, int rowNum) throws SQLException {
    return new City(rs.getLong("id"), rs.getString("name"), rs.getInt("population"));
}

}

The CityMapper maps a row of a result set to the City record.

**Note: ** Since Java records are immutable and do not follow the Java Beans specification, we cannot use the BeanPropertyRowMapper; we have to create our own mapper or use DataClassRowMapper.

com/zetcode/service/ICityService.java

package com.zetcode.service;

import com.zetcode.model.City;

import java.util.List;

public interface ICityService {

List<City> findAll();
City findById(Long id);

}

We have two contract methods.

com/zetcode/service/CityService.java

package com.zetcode.service;

import com.zetcode.mapper.CityMapper; import com.zetcode.model.City; import org.springframework.jdbc.core.JdbcTemplate; import org.springframework.stereotype.Service;

import java.util.List;

@Service public class CityService implements ICityService {

private final JdbcTemplate jtm;

public CityService(JdbcTemplate jtm) {
    this.jtm = jtm;
}

@Override
public List<City> findAll() {

    String sql = "SELECT * FROM cities";

    return jtm.query(sql, new CityMapper());
}

@Override
public City findById(Long id) {

    String sql = "SELECT * FROM cities WHERE id = ?";

    return jtm.queryForObject(sql, new CityMapper(), id);
}

}

We have the implementations of the two contract methods, using the CityMapper.

com/zetcode/MyRunner.java

package com.zetcode;

import com.zetcode.service.ICityService; import org.springframework.boot.CommandLineRunner; import org.springframework.stereotype.Component;

@Component public class MyRunner implements CommandLineRunner {

private final ICityService cityService;

public MyRunner(ICityService cityService) {
    this.cityService = cityService;
}

@Override
public void run(String... args) throws Exception {

    var city = cityService.findById(1L);
    System.out.println(city);

    var data = cityService.findAll();
    System.out.println(data);
}

}

In the MyRunner, we find one city by its Id and then find all cities.

com/zetcode/Application.java

package com.zetcode;

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

@SpringBootApplication public class Application {

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

}

The Application sets up the Spring Boot application.

$ ./gradlew bootRun … City[id=1, name=Bratislava, population=432000] [City[id=1, name=Bratislava, population=432000], City[id=2, name=Budapest, population=1759000], City[id=3, name=Prague, population=1280000], City[id=4, name=Warsaw, population=1748000], City[id=5, name=Los Angeles, population=3971000], City[id=6, name=New York, population=8550000], City[id=7, name=Edinburgh, population=464000], City[id=8, name=Berlin, population=3671000]] …

In this article we have worked with Spring Boot RowMapper.

Author

My name is Jan Bodnar, and I am a passionate programmer with extensive programming experience. I have been writing programming articles since 2007. To date, I have authored over 1,400 articles and 8 e-books. I possess more than ten years of experience in teaching programming.

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