Spring Boot - Runners

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Application Runner and Command Line Runner interfaces lets you to execute the code after the Spring Boot application is started. You can use these interfaces to perform any actions immediately after the application has started. This chapter talks about them in detail.

Application Runner

Application Runner is an interface used to execute the code after the Spring Boot application started. The example given below shows how to implement the Application Runner interface on the main class file.

DemoApplication.java

package com.tutorialspoint.demo;

import org.springframework.boot.ApplicationArguments;
import org.springframework.boot.ApplicationRunner;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;

@SpringBootApplication
public class DemoApplication implements ApplicationRunner {
   public static void main(String[] args) {
      SpringApplication.run(DemoApplication.class, args);
   }
   @Override
   public void run(ApplicationArguments arg0) throws Exception {
      System.out.println("Hello World from Application Runner");
   }
}

Console Output

Now, if you observe the console window output below Hello World from Application Runner, the println statement is executed after the Tomcat started.


  .   ____          _            __ _ _
 /\\ / ___'_ __ _ _(_)_ __  __ _ \ \ \ \
( ( )\___ | '_ | '_| | '_ \/ _` | \ \ \ \
 \\/  ___)| |_)| | | | | || (_| |  ) ) ) )
  '  |____| .__|_| |_|_| |_\__, | / / / /
 =========|_|==============|___/=/_/_/_/

[32m :: Spring Boot :: [39m              [2m (v3.3.3)[0;39m

[2m2024-09-04T12:05:41.902+05:30[0;39m [32m INFO[0;39m [35m12304[0;39m [2m---[0;39m [2m[demo] [           main][0;39m [2m[0;39m[36mc.tutorialspoint.demo.DemoApplication   [0;39m [2m:[0;39m Starting DemoApplication using Java 21.0.3 with PID 12304 (E:\Dev\demo\target\classes started by Tutorialspoint in E:\Dev\demo)
[2m2024-09-04T12:05:41.905+05:30[0;39m [32m INFO[0;39m [35m12304[0;39m [2m---[0;39m [2m[demo] [           main][0;39m [2m[0;39m[36mc.tutorialspoint.demo.DemoApplication   [0;39m [2m:[0;39m No active profile set, falling back to 1 default profile: "default"
[2m2024-09-04T12:05:43.427+05:30[0;39m [32m INFO[0;39m [35m12304[0;39m [2m---[0;39m [2m[demo] [           main][0;39m [2m[0;39m[36mo.s.b.w.embedded.tomcat.TomcatWebServer [0;39m [2m:[0;39m Tomcat initialized with port 8080 (http)
[2m2024-09-04T12:05:43.454+05:30[0;39m [32m INFO[0;39m [35m12304[0;39m [2m---[0;39m [2m[demo] [           main][0;39m [2m[0;39m[36mo.apache.catalina.core.StandardService  [0;39m [2m:[0;39m Starting service [Tomcat]
[2m2024-09-04T12:05:43.454+05:30[0;39m [32m INFO[0;39m [35m12304[0;39m [2m---[0;39m [2m[demo] [           main][0;39m [2m[0;39m[36mo.apache.catalina.core.StandardEngine   [0;39m [2m:[0;39m Starting Servlet engine: [Apache Tomcat/10.1.28]
[2m2024-09-04T12:05:43.528+05:30[0;39m [32m INFO[0;39m [35m12304[0;39m [2m---[0;39m [2m[demo] [           main][0;39m [2m[0;39m[36mo.a.c.c.C.[Tomcat].[localhost].[/]      [0;39m [2m:[0;39m Initializing Spring embedded WebApplicationContext
[2m2024-09-04T12:05:43.529+05:30[0;39m [32m INFO[0;39m [35m12304[0;39m [2m---[0;39m [2m[demo] [           main][0;39m [2m[0;39m[36mw.s.c.ServletWebServerApplicationContext[0;39m [2m:[0;39m Root WebApplicationContext: initialization completed in 1552 ms
[2m2024-09-04T12:05:44.120+05:30[0;39m [32m INFO[0;39m [35m12304[0;39m [2m---[0;39m [2m[demo] [           main][0;39m [2m[0;39m[36mo.s.b.w.embedded.tomcat.TomcatWebServer [0;39m [2m:[0;39m Tomcat started on port 8080 (http) with context path '/'
[2m2024-09-04T12:05:44.134+05:30[0;39m [32m INFO[0;39m [35m12304[0;39m [2m---[0;39m [2m[demo] [           main][0;39m [2m[0;39m[36mc.tutorialspoint.demo.DemoApplication   [0;39m [2m:[0;39m Started DemoApplication in 3.007 seconds (process running for 4.519)
Hello World from Application Runner

Command Line Runner

Command Line Runner is an interface. It is used to execute the code after the Spring Boot application started. The example given below shows how to implement the Command Line Runner interface on the main class file.

DemoApplication.java

package com.tutorialspoint.demo;

import org.springframework.boot.CommandLineRunner;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;

@SpringBootApplication
public class DemoApplication implements CommandLineRunner {
   public static void main(String[] args) {
      SpringApplication.run(DemoApplication.class, args);
   }
   @Override
   public void run(String... arg0) throws Exception {
      System.out.println("Hello world from Command Line Runner");
   }
}

Console Output

Look at the console window output below "Hello world from Command Line Runner" println statement is executed after the Tomcat started.


  .   ____          _            __ _ _
 /\\ / ___'_ __ _ _(_)_ __  __ _ \ \ \ \
( ( )\___ | '_ | '_| | '_ \/ _` | \ \ \ \
 \\/  ___)| |_)| | | | | || (_| |  ) ) ) )
  '  |____| .__|_| |_|_| |_\__, | / / / /
 =========|_|==============|___/=/_/_/_/

[32m :: Spring Boot :: [39m              [2m (v3.3.3)[0;39m

[2m2024-09-04T12:08:37.804+05:30[0;39m [32m INFO[0;39m [35m16908[0;39m [2m---[0;39m [2m[demo] [           main][0;39m [2m[0;39m[36mc.tutorialspoint.demo.DemoApplication   [0;39m [2m:[0;39m Starting DemoApplication using Java 21.0.3 with PID 16908 (E:\Dev\demo\target\classes started by Tutorialspoint in E:\Dev\demo)
[2m2024-09-04T12:08:37.808+05:30[0;39m [32m INFO[0;39m [35m16908[0;39m [2m---[0;39m [2m[demo] [           main][0;39m [2m[0;39m[36mc.tutorialspoint.demo.DemoApplication   [0;39m [2m:[0;39m No active profile set, falling back to 1 default profile: "default"
[2m2024-09-04T12:08:38.772+05:30[0;39m [32m INFO[0;39m [35m16908[0;39m [2m---[0;39m [2m[demo] [           main][0;39m [2m[0;39m[36mo.s.b.w.embedded.tomcat.TomcatWebServer [0;39m [2m:[0;39m Tomcat initialized with port 8080 (http)
[2m2024-09-04T12:08:38.786+05:30[0;39m [32m INFO[0;39m [35m16908[0;39m [2m---[0;39m [2m[demo] [           main][0;39m [2m[0;39m[36mo.apache.catalina.core.StandardService  [0;39m [2m:[0;39m Starting service [Tomcat]
[2m2024-09-04T12:08:38.786+05:30[0;39m [32m INFO[0;39m [35m16908[0;39m [2m---[0;39m [2m[demo] [           main][0;39m [2m[0;39m[36mo.apache.catalina.core.StandardEngine   [0;39m [2m:[0;39m Starting Servlet engine: [Apache Tomcat/10.1.28]
[2m2024-09-04T12:08:38.841+05:30[0;39m [32m INFO[0;39m [35m16908[0;39m [2m---[0;39m [2m[demo] [           main][0;39m [2m[0;39m[36mo.a.c.c.C.[Tomcat].[localhost].[/]      [0;39m [2m:[0;39m Initializing Spring embedded WebApplicationContext
[2m2024-09-04T12:08:38.842+05:30[0;39m [32m INFO[0;39m [35m16908[0;39m [2m---[0;39m [2m[demo] [           main][0;39m [2m[0;39m[36mw.s.c.ServletWebServerApplicationContext[0;39m [2m:[0;39m Root WebApplicationContext: initialization completed in 980 ms
[2m2024-09-04T12:08:39.185+05:30[0;39m [32m INFO[0;39m [35m16908[0;39m [2m---[0;39m [2m[demo] [           main][0;39m [2m[0;39m[36mo.s.b.w.embedded.tomcat.TomcatWebServer [0;39m [2m:[0;39m Tomcat started on port 8080 (http) with context path '/'
[2m2024-09-04T12:08:39.192+05:30[0;39m [32m INFO[0;39m [35m16908[0;39m [2m---[0;39m [2m[demo] [           main][0;39m [2m[0;39m[36mc.tutorialspoint.demo.DemoApplication   [0;39m [2m:[0;39m Started DemoApplication in 1.844 seconds (process running for 2.693)
Hello world from Command Line Runner
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