Spring Boot ApplicationRunner
June 19, 2024
Spring Boot ApplicationRunner is a runner that runs before the application gets ready to serve traffic. It is useful to run any logic before application starts up.
Spring Boot has two runners,
CommandLineRunner and ApplicationRunner with the difference that CommandLineRunner accepts arguments as string array whereas ApplicationRunner accepts arguments as ApplicationArguments. Both are functional interface with a method named as run.
Find the method declaration of
ApplicationRunner from Spring doc.
void run(ApplicationArguments args)
ApplicationArguments: Interface whose role is to provide access to the arguments used to run
SpringApplication in Spring Boot application. ApplicationArguments has following methods.
1.
boolean containsOption(String name)
List<String> getNonOptionArgs()
Set<String> getOptionNames()
List<String> getOptionValues(String name)
String[] getSourceArgs()
Using ApplicationRunner
Create a component by implementingApplicationRunner.
@Component
public class MyAppRunner implements ApplicationRunner {
@Override
public void run(ApplicationArguments args) throws Exception {
Arrays.stream(args.getSourceArgs()).forEach(arg -> System.out.println(arg));
}
}
SpringApplication.
Find Spring Boot Main class.
@SpringBootApplication
public class MyApp {
public static void main(String[] args) {
SpringApplication application = new SpringApplication(MyApp.class);
application.run(args);
}
}
java -jar spring-boot-app.jar Hello
Hello
Implement ApplicationRunner by Main Class
We can create runner directly by implementing Main class. Overdriverun method and perform any logic.
@SpringBootApplication
public class TadStackApplication implements ApplicationRunner {
public static void main(String[] args) {
SpringApplication application = new SpringApplication(TadStackApplication.class);
application.run(args);
System.out.println("----Done----");
}
@Override
public void run(ApplicationArguments args) throws Exception {
System.out.println("Running scripts...");
}
}
Running scripts... ----Done----
Register Runner using @Bean
We can register runner with Spring using@Bean annotation.
@SpringBootApplication
public class TadStackApplication {
public static void main(String[] args) {
SpringApplication application = new SpringApplication(TadStackApplication.class);
application.run(args);
System.out.println("----Done----");
}
}
@Configuration
class TSAppConfig {
@Bean
public MyTSRunner getMyTSRunner() {
return new MyTSRunner();
}
}
class MyTSRunner implements ApplicationRunner {
@Override
public void run(ApplicationArguments args) throws Exception {
System.out.println("Running scripts...");
}
}
Creating ApplicationRunner using Lambda Expression
ApplicationRunner is a functional interface. We can create their object using lambda expression.
@SpringBootApplication
public class TadStackApplication {
public static void main(String[] args) {
SpringApplication application = new SpringApplication(TadStackApplication.class);
application.run(args);
System.out.println("----Done----");
}
}
@Configuration
class TSAppConfig {
@Bean
public ApplicationRunner getMyTSRunner() {
return args -> {
System.out.println("args: " + args.getOptionNames());
};
}
}
mvn spring-boot:run -Dspring-boot.run.arguments="--server.port=8282 --spring.profiles.active=dev"
args: [server.port, spring.profiles.active] ----Done----
Set Order
When we have more than one runner, we can set the ordering of runners usingOrdered interface or @Order annotation.
Find the first runner with order one.
@Order(1)
@Component
public class XyzRunner implements ApplicationRunner {
@Override
public void run(ApplicationArguments args) throws Exception {
System.out.println("XyzRunner...");
}
}
@Order(2)
@Component
public class AbcRunner implements ApplicationRunner {
@Override
public void run(ApplicationArguments args) throws Exception {
System.out.println("AbcRunner...");
}
}
XyzRunner... AbcRunner...
Usability of ApplicationRunner
1. Database transaction :ApplicationRunner is useful to perform database transaction before application starts up. Suppose our application has to insert some seed data in the database before handling traffic, we can use the runner.
2. Running Scheduler : Application can run schedulers before application starts handling traffic. Runner is useful to run schedulers using arguments from command line.
3. Logging Messages : We can log messages before application starts up.