Spring Boot启动类加载器

什么是启动类加载器

就是SpringBoot启动后，要立马执行的程序，这时候就需要启动类加载器完整这个要求。

启动类加载器实践

1、创建第一个启动类加载器（方式1）

1）、创建启动类加载器，实现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）、启动项目，输出如下

2、多个类加载器，如何控制调用顺序。

只需要增加Order注解即可

第一个启动类加载器

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

　　

第二个启动类加载器

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

　　

然后启动项目，输出如下

2、创建类加载器，方式二

1）、创建FirstApplicationRunner 类，实现 ApplicationRunner接口，然后设置Order为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，创建SecondApplicationRunner 类，实现 ApplicationRunner接口，然后设置Order为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）启动项目，查看输出结果如下

3、启动类加载器原理

进入run方法，启动类加载器的入口是callRunners方法

进入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);
			}
		}
	}

　　

将实现ApplicationRunner接口的类实例增加到runners列表中

将实现CommandLineRunner接口的类实例增加到runners列表中。

然后进行排序AnnotationAwareOrderComparator.sort(runners);

排序完毕后依次调用callRunner方法

callRunner方法实现如下。里面调用各自的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);
		}
	}