CommandLineRunner Interface in Spring Boot

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Hello Friends!, today we are going to learn about CommandLineRunner Interface.

Spring Boot provides two interfaces, CommandLineRunner and ApplicationRunner, to run specific pieces of code when an application is fully started. These interfaces get called just before run() once SpringApplication completes.

how to create Spring Boot Application using the below ways.

Using Spring Initializr.

Application in STS.

Application with Eclipse and Maven manually

CommandLineRunner Interface

Example implementation of CommandLineRunner interface as follow.

you can implement CommandLineRunner interface as follow, run() gives access to the raw String array of incoming main method arguments.

package com.gyanideveloper.springboot.hook.command;

import java.util.Arrays;

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.boot.CommandLineRunner;
import org.springframework.stereotype.Component;

@Component
public class CommandRunner implements CommandLineRunner {

	private static final Logger logger = LoggerFactory.getLogger(CommandRunner.class);

	@Override
	public void run(String... args) throws Exception {
		logger.info("Application started with CommandLineRunner::run(-) ::" + Arrays.toString(args));
	}

}

CommandLineRunner interface provides single run() , it gives access to the raw String array of incoming main method arguments.

If you need access to ApplicationArguments instead of the raw String array consider using ApplicationRunner.

if you run the application, you can see application console log as follows, we have provides --server.port=8383 arguments while starting the application.

  .   ____          _            __ _ _
 /\\ / ___'_ __ _ _(_)_ __  __ _ \ \ \ \
( ( )\___ | '_ | '_| | '_ \/ _` | \ \ \ \
 \\/  ___)| |_)| | | | | || (_| |  ) ) ) )
  '  |____| .__|_| |_|_| |_\__, | / / / /
 =========|_|==============|___/=/_/_/_/
 :: Spring Boot ::        (v2.3.0.RELEASE)

2020-06-01 19:16:41.705  INFO 10764 --- [           main] c.g.s.hook.SpringBootHookApplication     : Starting SpringBootHookApplication on DESKTOP-R5VMSGQ with PID 10764 (F:\workspace-spring-tool-suite-4-4.6.1.RELEASE\spring-boot-hook\target\classes started by Gyani in F:\workspace-spring-tool-suite-4-4.6.1.RELEASE\spring-boot-hook)
2020-06-01 19:16:41.708  INFO 10764 --- [           main] c.g.s.hook.SpringBootHookApplication     : No active profile set, falling back to default profiles: default
2020-06-01 19:16:42.331  INFO 10764 --- [           main] c.g.s.hook.SpringBootHookApplication     : Started SpringBootHookApplication in 0.988 seconds (JVM running for 1.509)
2020-06-01 19:16:42.334  INFO 10764 --- [           main] c.g.s.hook.command.CommandRunner         : Application started with CommandLineRunner::run(-) ::[--server.port=8383]

Ordering CommandLineRunner Interface

we can use multiple CommandLineRunner or ApplicationRunner beans in a single application. Spring automatically picks them up, in case of if we want to Order them, we can use the following two ways.

  • Using  @Order annotation
  • implementing Ordered interface

Using  @Order annotation

@Order annotation defines the sort order for an annotated component.we can provide the priority for a component.

 Let’s see the example code for more clarity.

package com.gyanideveloper.springboot.hook.command;

import java.util.Arrays;

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.boot.CommandLineRunner;
import org.springframework.core.annotation.Order;
import org.springframework.stereotype.Component;

@Component
@Order(1)
public class CommandRunner implements CommandLineRunner {

	private static final Logger logger = LoggerFactory.getLogger(CommandRunner.class);

	@Override
	public void run(String... args) throws Exception {
		logger.info("Application started with CommandLineRunner::run(-) ::" + Arrays.toString(args));
	}

}

implementing Ordered interface

we need to implement Ordered interface and provide the implementation for getOrder() method

Let’s see the example code for more clarity.

package com.gyanideveloper.springboot.hook.command;

import java.util.Arrays;

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.boot.CommandLineRunner;
import org.springframework.core.Ordered;
import org.springframework.stereotype.Component;

@Component
public class CommandRunnerSecond implements CommandLineRunner, Ordered {

	private static final Logger logger = LoggerFactory.getLogger(CommandRunnerSecond.class);

	@Override
	public void run(String... args) throws Exception {
		logger.info("Application started with CommandRunnerSecond::run(-) ::" + Arrays.toString(args));
	}

	@Override
	public int getOrder() {
		return 2;
	}

}

if you run the application, you can see application console log as follows, we have provides --server.port=8383 arguments while starting the application.

  .   ____          _            __ _ _
 /\\ / ___'_ __ _ _(_)_ __  __ _ \ \ \ \
( ( )\___ | '_ | '_| | '_ \/ _` | \ \ \ \
 \\/  ___)| |_)| | | | | || (_| |  ) ) ) )
  '  |____| .__|_| |_|_| |_\__, | / / / /
 =========|_|==============|___/=/_/_/_/
 :: Spring Boot ::        (v2.3.0.RELEASE)

2020-06-01 22:25:59.148  INFO 9664 --- [           main] c.g.s.hook.SpringBootHookApplication     : Starting SpringBootHookApplication on DESKTOP-R5VMSGQ with PID 9664 (F:\workspace-spring-tool-suite-4-4.6.1.RELEASE\spring-boot-hook\target\classes started by Sada in F:\workspace-spring-tool-suite-4-4.6.1.RELEASE\spring-boot-hook)
2020-06-01 22:25:59.154  INFO 9664 --- [           main] c.g.s.hook.SpringBootHookApplication     : No active profile set, falling back to default profiles: default
2020-06-01 22:25:59.911  INFO 9664 --- [           main] c.g.s.hook.SpringBootHookApplication     : Started SpringBootHookApplication in 1.268 seconds (JVM running for 2.27)
2020-06-01 22:25:59.916  INFO 9664 --- [           main] c.g.s.hook.command.CommandRunner         : Application started with CommandLineRunner::run(-) ::[--server.port=8383]
2020-06-01 22:25:59.917  INFO 9664 --- [           main] c.g.s.hook.command.CommandRunnerSecound  : Application started with CommandRunnerSecond::run(-) ::[--server.port=8383]

CommandLineRunner as @Bean

Example implementation of CommandLineRunner as @Bean follow.

package com.gyanideveloper.springboot.hook;

import java.util.Arrays;

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.boot.CommandLineRunner;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.context.annotation.Bean;

@SpringBootApplication
public class SpringBootHookApplication {

	private static final Logger logger = LoggerFactory.getLogger(SpringBootHookApplication.class);

	@Bean
	public CommandLineRunner getRunner() {
		return args -> {
			logger.info("Application started with @Bean CommandLineRunner::run(-) ::" + Arrays.toString(args));
		};
	}

	public static void main(String[] args) {
		SpringApplication.run(SpringBootHookApplication.class, args);
	}

}

if you run the application, you can see application console log as follows, we have provides --server.port=8383 arguments while starting the application.

2020-06-01 22:49:54.240 INFO 10096 --- [ main] c.g.s.hook.SpringBootHookApplication : Application started with @Bean CommandLineRunner::run(-) ::[--server.port=8383]

When to use it

When you want to execute some piece of code exactly before the application startup completes.

Final Note

we have learn CommandLineRunner interface in details. full example code is available on GitHub

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