Spring Boot啟動類加載器

什么是啟動類加載器

就是SpringBoot啟動后，要立馬執行的程序，這時候就需要啟動類加載器完整這個要求。

 

啟動類加載器實踐

1、創建第一個啟動類加載器（方式1）

1）、創建啟動類加載器，實現CommandLineRunner接口

@Component
public class FirstCommandlineRunner  implements CommandLineRunner{
    @Override
    public void run(String... args) throws Exception {
        System.out.println("\u001B[32m >>> startup fist runner<<<");
    }
}

　　

2）、啟動項目，輸出如下

 

2、多個類加載器，如何控制調用順序。

只需要增加Order注解即可

第一個啟動類加載器

@Component
@Order(1)
public class FirstCommandlineRunner  implements CommandLineRunner{
    @Override
    public void run(String... args) throws Exception {
        System.out.println("\u001B[32m >>> startup fist runner<<<");
    }
}

　　

第二個啟動類加載器

@Component
@Order(2)
public class SecondCommandlineRunner implements CommandLineRunner{
    @Override
    public void run(String... args) throws Exception {
        System.out.println("\u001B[32m >>> startup second runner<<<");
    }
}

　　

然后啟動項目，輸出如下

 

 

 

 

2、創建類加載器，方式二

1）、創建FirstApplicationRunner 類，實現 ApplicationRunner接口，然后設置Order為1

@Component
@Order(1)
public class FirstApplicationRunner  implements ApplicationRunner{
    @Override
    public void run(ApplicationArguments args) throws Exception {
        System.out.println("\u001B[32m >>> startup first application runner<<<");

    }
}

　　

2) 同理，創建SecondApplicationRunner 類，實現 ApplicationRunner接口，然后設置Order為2

@Component
@Order(2)
public class SecondApplicationRunner implements ApplicationRunner{
    @Override
    public void run(ApplicationArguments args) throws Exception {
        System.out.println("\u001B[32m >>> startup second application runner<<<");

    }
}

　　

3）啟動項目，查看輸出結果如下

 

3、啟動類加載器原理

進入run方法，啟動類加載器的入口是callRunners方法

 

 

進入callRunners方法

	private void callRunners(ApplicationContext context, ApplicationArguments args) {
		List<Object> runners = new ArrayList<>();
		runners.addAll(context.getBeansOfType(ApplicationRunner.class).values());
		runners.addAll(context.getBeansOfType(CommandLineRunner.class).values());
		AnnotationAwareOrderComparator.sort(runners);
		for (Object runner : new LinkedHashSet<>(runners)) {
			if (runner instanceof ApplicationRunner) {
				callRunner((ApplicationRunner) runner, args);
			}
			if (runner instanceof CommandLineRunner) {
				callRunner((CommandLineRunner) runner, args);
			}
		}
	}

　　

將實現ApplicationRunner接口的類實例增加到runners列表中

將實現CommandLineRunner接口的類實例增加到runners列表中。

然后進行排序AnnotationAwareOrderComparator.sort(runners);

排序完畢后依次調用callRunner方法

 

callRunner方法實現如下。里面調用各自的run方法

	private void callRunner(ApplicationRunner runner, ApplicationArguments args) {
		try {
			(runner).run(args);
		}
		catch (Exception ex) {
			throw new IllegalStateException("Failed to execute ApplicationRunner", ex);
		}
	}

	private void callRunner(CommandLineRunner runner, ApplicationArguments args) {
		try {
			(runner).run(args.getSourceArgs());
		}
		catch (Exception ex) {
			throw new IllegalStateException("Failed to execute CommandLineRunner", ex);
		}
	}