Spring Boot RowMapper

last modified July 28, 2023

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

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

Java record

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

We can useDataClassRowMapper for a seamless integration with Javarecords. See theSpring BootDataClassRowMapper tutorial.

Spring Boot RowMapper example

The following application uses aRowMapper to map a result setrow to aCity 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. TheRowMapper resides inspring-boot-starter-jdbc.

spring.main.banner-mode=offspring.sql.init.platform=h2spring.datasource.driverClassName=org.h2.Driverspring.datasource.url=jdbc:h2:mem:testdb

In theapplication.properties, we turn off the Spring Boot bannerand 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 aCity record. Most of the boilderplate for a typicalJava 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"));    }}

TheCityMapper maps a row of a result set to theCityrecord.

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;@Servicepublic 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 theCityMapper.

package com.zetcode;import com.zetcode.service.ICityService;import org.springframework.boot.CommandLineRunner;import org.springframework.stereotype.Component;@Componentpublic 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 theMyRunner, we find one city by its Id and then find allcities.

package com.zetcode;import org.springframework.boot.SpringApplication;import org.springframework.boot.autoconfigure.SpringBootApplication;@SpringBootApplicationpublic class Application {    public static void main(String[] args) {        SpringApplication.run(Application.class, args);    }}

TheApplication 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 extensiveprogramming experience. I have been writing programming articles since 2007.To date, I have authored over 1,400 articles and 8 e-books. I possess morethan ten years of experience in teaching programming.

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