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.

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.

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.

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

This SQL script creates the cities table.

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.

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.

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.

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.

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.

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.

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 many years of programming experience. I have been writing programming articles since 2007. So far, I have written over 1400 articles and 8 e-books. I have over eight years of experience in teaching programming.

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