Spring Boot 入门 - 进阶篇（6）- 启动加载(CommandLineRunner)

启动成功后可以通过以下方法运行自己的初始代码：

• @PostConstruct注解
• ApplicationReadyEvent事件
• CommandLineRunner/ApplicationRunner接口

@Component
public class StartUpInit {

  @Autowired
  private SomeService service;

  @PostConstruct
  public void init(){
     // ...
  }

}

@Component
public class GeneralEventHandler {

    @EventListener
    public void handleApplicationReady(ApplicationReadyEvent event) {
        log.info("The application is ready to service requests..");
    }

}

Spring Boot提供了两个接口：CommandLineRunner、ApplicationRunner，用于启动应用时做特殊处理，这些代码会在SpringApplication的run()方法运行完成之前被执行。
通常用于应用启动前的特殊代码执行、特殊数据加载、垃圾数据清理、微服务的服务发现注册、系统启动成功后的通知等。相当于Spring的ApplicationListener、Servlet的ServletContextListener。

CommandLineRunner 和 ApplicationRunner 的区别是run()方法的参数不同。

（1）CommandLineRunner：参数是字符串数组

@Component
public class CommandLineAppStartupRunner implements CommandLineRunner {
  private static final Logger logger = LoggerFactory.getLogger(CommandLineAppStartupRunner.class);

  @Override
  public void run(String... args) throws Exception {
    logger.info("Application started with command-line arguments: {} . \n To kill this application, press Ctrl + C.", Arrays.toString(args));
  }
}

（2）ApplicationRunner：参数被放入ApplicationArguments
通过getOptionNames()、getOptionValues()、getSourceArgs()获取参数

@Component
public class AppStartupRunner implements ApplicationRunner {
  private static final Logger logger = LoggerFactory.getLogger(AppStartupRunner.class);

  @Override
  public void run(ApplicationArguments args) throws Exception {
    logger.info("Your application started with option names : {}", args.getOptionNames());
  }
}

也可以两个接口同时实现，但是没有必要。

@Component
public class StartupRunner implements CommandLineRunner, ApplicationRunner  {
  private static final Logger logger = LoggerFactory.getLogger(CommandLineAppStartupRunner.class);

  @Override
  public void run(String... args) throws Exception {
    logger.info("Application started with command-line arguments: {} . \n To kill this application, press Ctrl + C.", Arrays.toString(args));
  }
  
  @Override
  public void run(ApplicationArguments args) throws Exception {
    logger.info("Your application started with option names : {}", args.getOptionNames());
  }
}

也可以通过@Bean定义

@Configuration
public class RunnerConfig {

	@Bean
	public CommandLineRunner runner(){
	  return new CommandLineRunner() {
	    public void run(String... args){
	      System.out.println("CommandLineRunner run()");
	    }
	  };
	}

}

（3）通过@Order设置执行顺序

@Component
@Order(3)
public class Runner1 implements CommandLineRunner {
  @Override
  public void run(String... args) throws Exception {
    System.out.println("Runner1 run()");
  }
}

@Component
@Order(2)
public class Runner2 implements CommandLineRunner {
  @Override
  public void run(String... args) throws Exception {
    System.out.println("Runner2 run()");
  }
}

@Component
@Order(1)
public class Runner3 implements CommandLineRunner {
  @Override
  public void run(String... args) throws Exception {
    System.out.println("Runner3 run()");
  }
}

（4）注入Bean
CommandLineRunner在被执行时，Spring内部已经启动完成，可以注入Spring的Bean。

@Component
public class StartupRunner implements CommandLineRunner {

  @Autowired
  private SampleService sampleService;

  @Override
  public void run(String... args) throws Exception {
    sampleService.executeSample();
  }
  
}