Some Tips Of Spring Boot

Accessing Application Arguments

If you need to access the application arguments that were passed to?SpringApplication.run(…), you can inject a?org.springframework.boot.ApplicationArguments?bean. The?ApplicationArguments?interface provides access to both the raw?String[]?arguments as well as parsed?option?and?non-option?arguments, as shown in the following example:

import?java.util.List;

import?org.springframework.boot.ApplicationArguments;
import?org.springframework.stereotype.Component;

@Component
public?class?MyBean?{

????public?MyBean(ApplicationArguments?args)?{
????????boolean?debug?=?args.containsOption("debug");
????????List<String>?files?=?args.getNonOptionArgs();
????????if?(debug)?{
????????????System.out.println(files);
????????}
????????//?if?run?with?"--debug?logfile.txt"?prints?["logfile.txt"]
????}

}

Spring Boot also registers a?CommandLinePropertySource?with the Spring?Environment. This lets you also inject single application arguments by using the?@Value?annotation.

Using the ApplicationRunner or CommandLineRunner

If you need to run some specific code once the?SpringApplication?has started, you can implement the?ApplicationRunner?or?CommandLineRunner?interfaces. Both interfaces work in the same way and offer a single?run?method, which is called just before?SpringApplication.run(…)?completes.

The?CommandLineRunner?interfaces provides access to application arguments as a string array, whereas the?ApplicationRunner?uses the?ApplicationArguments?interface discussed earlier. The following example shows a?CommandLineRunner?with a?run?method:

import?org.springframework.boot.CommandLineRunner;
import?org.springframework.stereotype.Component;

@Component
public?class?MyCommandLineRunner?implements?CommandLineRunner?{

????@Override
????public?void?run(String...?args)?{
????????//?Do?something...
????}

}

If several?CommandLineRunner?or?ApplicationRunner?beans are defined that must be called in a specific order, you can additionally implement the?org.springframework.core.Ordered?interface or use the?org.springframework.core.annotation.Order?annotation.

Application Exit

Each?SpringApplication?registers a shutdown hook with the JVM to ensure that the?ApplicationContext?closes gracefully on exit. All the standard Spring lifecycle callbacks (such as the?DisposableBean?interface or the?@PreDestroy?annotation) can be used.

In addition, beans may implement the?org.springframework.boot.ExitCodeGenerator?interface if they wish to return a specific exit code when?SpringApplication.exit()?is called. This exit code can then be passed to?System.exit()?to return it as a status code, as shown in the following example:

import?org.springframework.boot.ExitCodeGenerator;
import?org.springframework.boot.SpringApplication;
import?org.springframework.boot.autoconfigure.SpringBootApplication;
import?org.springframework.context.annotation.Bean;

@SpringBootApplication
public?class?MyApplication?{

????@Bean
????public?ExitCodeGenerator?exitCodeGenerator()?{
????????return?()?->?42;
????}

????public?static?void?main(String[]?args)?{
????????System.exit(SpringApplication.exit(SpringApplication.run(MyApplication.class,?args)));
????}

}

Also, the?ExitCodeGenerator?interface may be implemented by exceptions. When such an exception is encountered, Spring Boot returns the exit code provided by the implemented?getExitCode()?method.

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