Spring Boot findById
Spring Boot findById tutorial shows how to retrieve an entity by its Id using CrudRepository's findById method.
Spring Boot findById
last modified July 18, 2023
Spring Boot findById tutorial shows how to retrieve an entity by its Id using CrudRepository’s findById method.
Spring is a popular Java/Kotlin application framework for creating enterprise applications. Spring Boot is an evolution of Spring framework which helps create stand-alone, production-grade Spring based applications with minimal effort.
CrudRepository
CrudRepository interface provides generic CRUD operations on a repository for a specific type. Its findById method retrieves an entity by its id. The return value is Optional<T>.
Optional<T> is a container object which may or may not contain a non-null value. If a value is present, isPresent returns true and get returns the value. The ifPresent invokes the specified method if the value is present; otherwise nothing is done.
Spring Boot findById example
The following application sets up a repository of City objects. In the console runner we retrieve city objects by their Ids.
build.gradle … src ├── main │ ├── java │ │ └── com │ │ └── zetcode │ │ ├── Application.java │ │ ├── MyRunner.java │ │ ├── model │ │ │ └── City.java │ │ ├── repository │ │ │ └── CityRepository.java │ │ └── service │ │ ├── CityService.java │ │ └── ICityService.java │ └── resources │ ├── application.properties │ ├── data-h2.sql │ └── schema-h2.sql └── test ├── java └── resources
This is the project structure.
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-data-jpa’ implementation ‘org.springframework.boot:spring-boot-starter-json’ runtimeOnly ‘com.h2database:h2’ }
The build.gradle file contains dependencies for Spring Data JPA, Jackson, and H2 database.
resources/application.properties
spring.main.banner-mode=off spring.sql.init.platform=h2 spring.jpa.hibernate.ddl-auto=none
The application.properties is Spring Boot’s main configuration file. The Spring Boot banner is turned off with the spring.main.banner-mode property.
The spring.sql.init.platform sets the vendor name of the database. It is used in the initialization scripts. The spring.jpa.hibernate.ddl-auto disables the automatic creation of schemas from entities.
resources/schema-h2.sql
CREATE TABLE cities(id INT PRIMARY KEY AUTO_INCREMENT, name VARCHAR(255), population INT);
When the application is started, the schema-h2.sql script is executed. It creates a new database 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(‘Suzhou’, 4327066); INSERT INTO cities(name, population) VALUES(‘Zhengzhou’, 4122087); INSERT INTO cities(name, population) VALUES(‘Berlin’, 3671000);
The table is filled with data from the data-h2.sql file.
com/zetcode/model/City.java
package com.zetcode.model;
import java.util.Objects; import jakarta.persistence.Entity; import jakarta.persistence.GeneratedValue; import jakarta.persistence.GenerationType; import jakarta.persistence.Id; import jakarta.persistence.Table;
@Entity @Table(name = “cities”) public class City {
@Id
@GeneratedValue(strategy = GenerationType.AUTO)
private Long id;
private String name;
private int population;
public City() {
}
public City(String name, int population) {
this.name = name;
this.population = population;
}
public Long getId() {
return id;
}
public void setId(Long id) {
this.id = id;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public int getPopulation() {
return population;
}
public void setPopulation(int population) {
this.population = population;
}
@Override
public boolean equals(Object o) {
if (this == o) return true;
if (o == null || getClass() != o.getClass()) return false;
City city = (City) o;
return population == city.population &&
Objects.equals(name, city.name);
}
@Override
public int hashCode() {
return Objects.hash(name, population);
}
@Override
public String toString() {
var builder = new StringBuilder();
builder.append("City{id=").append(id).append(", name=")
.append(name).append(", population=")
.append(population).append("}");
return builder.toString();
}
}
This is the City entity.
com/zetcode/repository/CityRepository.java
package com.zetcode.repository;
import com.zetcode.model.City; import org.springframework.data.repository.CrudRepository; import org.springframework.stereotype.Repository;
@Repository public interface CityRepository extends CrudRepository<City, Long> {
}
By extending from the Spring CrudRepository, we have some basic methods for our data repository implemented.
com/zetcode/service/ICityService.java
package com.zetcode.service;
import com.zetcode.model.City;
import java.util.Optional;
public interface ICityService {
Optional<City> findById(Long id);
}
ICityService provides a contract method to get a city by its Id.
com/zetcode/service/CityService.java
package com.zetcode.service;
import com.zetcode.model.City; import com.zetcode.repository.CityRepository; import org.springframework.beans.factory.annotation.Autowired; import org.springframework.stereotype.Service;
import java.util.Optional;
@Service public class CityService implements ICityService {
private final CityRepository cityRepository;
@Autowired
public CityService(CityRepository cityRepository) {
this.cityRepository = cityRepository;
}
@Override
public Optional<City> findById(Long id) {
return cityRepository.findById(id);
}
}
CityService contains the implementation of the findById method. We use the repository to retrieve data from the database.
private final CityRepository cityRepository;
public CityService(CityRepository cityRepository) { this.cityRepository = cityRepository; }
CityRepository is injected.
@Override public Optional<City> findById(Long id) {
return cityRepository.findById(id);
}
The findById returns Optional<City>.
com/zetcode/MyRunner.java
package com.zetcode;
import com.zetcode.service.ICityService; import org.springframework.beans.factory.annotation.Autowired; import org.springframework.boot.CommandLineRunner; import org.springframework.stereotype.Component;
@Component public class MyRunner implements CommandLineRunner {
private final ICityService cityService;
@Autowired
public MyRunner(ICityService cityService) {
this.cityService = cityService;
}
@Override
public void run(String... args) throws Exception {
var id1 = 2L;
cityService.findById(id1).ifPresent(System.out::println);
var id2 = 24L;
var val = cityService.findById(id2);
if (val.isPresent()) {
System.out.println(val.get());
} else {
System.out.printf("No city found with id %d%n", id2);
}
}
}
In the MyRunner, we look for two city entities.
var id1 = 2L; cityService.findById(id1).ifPresent(System.out::println);
We find a city by its Id and if it is present, we print it to the console. Otherwise, nothing is printed.
var id2 = 24L; var val = cityService.findById(id2);
if (val.isPresent()) { System.out.println(val.get()); } else { System.out.printf(“No city found with id %d%n”, id2); }
In the second case, we check the presence of a value with isPresent. If a value is present, we print it. If not, we print a message that the city was not found.
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=2, name=Budapest, population=1759000} No city found with id 24 …
We run the application.
In this article we have showed how to find a specific entity with CrudRepository’s findById method.
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.
