Spring Boot CommandLineRunner
last modified August 2, 2023
In this article we show how to run beans using CommandLineRunner interface.
Spring is a popular Java application framework and Spring Boot is an evolution of Spring that helps create stand-alone, production-grade Spring based applications easily.
CommandLineRunner
CommandLineRunner is an interface used to indicate that a bean
should run when it is contained within a SpringApplication. A Spring Boot
application can have multiple beans implementing CommandLineRunner.
These can be ordered with @Order.
Spring Boot CommandLineRunner example
The following application demonstrates the usage of
CommandLineRunner. It creates cities in a H2 in-memory database and
later lists them.
build.gradle
...
src
├───main
│ ├───java
│ │ └───com
│ │ └───zetcode
│ │ │ Application.java
│ │ │ MyRunner.java
│ │ ├───model
│ │ │ City.java
│ │ └───repository
│ │ CityRepository.java
│ └───resources
│ application.properties
└───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'
runtimeOnly 'com.h2database:h2'
}
This is the Gradle build file. We use the H2 database and Spring Data JPA.
spring.main.banner-mode=off
The application.properties is the main configuration file in Spring
Boot. With spring.main.banner-mode=off we turn off the Spring
banner.
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 int hashCode() {
int hash = 7;
hash = 79 * hash + Objects.hashCode(this.id);
hash = 79 * hash + Objects.hashCode(this.name);
hash = 79 * hash + this.population;
return hash;
}
@Override
public boolean equals(Object obj) {
if (this == obj) {
return true;
}
if (obj == null) {
return false;
}
if (getClass() != obj.getClass()) {
return false;
}
final City other = (City) obj;
if (this.population != other.population) {
return false;
}
if (!Objects.equals(this.name, other.name)) {
return false;
}
return Objects.equals(this.id, other.id);
}
@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 model, which has the following properties:
id, name, and population.
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> {
}
CityRepository has some generic CRUD operations on a repository for
a City.
package com.zetcode;
import com.zetcode.model.City;
import com.zetcode.repository.CityRepository;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.boot.CommandLineRunner;
import org.springframework.stereotype.Component;
@Component
public class MyRunner implements CommandLineRunner {
private static final Logger logger = LoggerFactory.getLogger(MyRunner.class);
private final CityRepository repository;
public MyRunner(CityRepository repository) {
this.repository = repository;
}
@Override
public void run(String... args) throws Exception {
repository.deleteAll();
repository.save(new City("Bratislava", 432000));
repository.save(new City("Budapest", 1759000));
repository.save(new City("Prague", 1280000));
repository.findAll().forEach((city) -> {
logger.info("{}", city);
});
}
}
By implementing the CommandLineRunner, the run
method of the MyRunner class will be executed after the application
starts.
@Component
public class MyRunner implements CommandLineRunner {
MyRunner is also decorated with @Component, so it will
be autodetected and registered as well.
private final CityRepository repository;
public MyRunner(CityRepository repository) {
this.repository = repository;
}
We inject the CityRepository bean into the repository
field.
@Override
public void run(String... args) throws Exception {
repository.save(new City("Bratislava", 432000));
repository.save(new City("Budapest", 1759000));
repository.save(new City("Prague", 1280000));
repository.findAll().forEach((city) -> {
logger.info("{}", city);
});
In the run method, we create three cities and later
find all of them and print them to the console.
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);
}
}
Application is the entry point which sets up Spring Boot
application.
$ ./gradlew bootRun
We run the application.
In this article we have shown how to use CommandLineRunner
interface to create a bean that is run when the application starts.
