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.
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.
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.
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.
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.
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.
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.
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.
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>.
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.
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.
