SpringBoot上下文初始器加载过程详解

SpringBoot上下文初始器加载过程详解

利用 Spring 工厂加载机制，实例化 ApplicationContexQiJUqATtInitializer 实现类，并排序对象集合。

关键方法

private Collection getSpringFactoriesInstances(Class type,

Class>[] parameterTypes, Object... args) {

ClassLoader classLoader = Thread.currentQiJUqATThread().getContextClassLoader();

// Use names and ensure unique to protect against duplicates

Set names = new LinkedHashSet<>(

SpringFactoriesLoader.loadFactoryNames(type, classLoader));

List instances = createSpringFactoriesInstances(type, parameterTypes,

classLoader, args, names);

AnnotationAwareOrderComparator.sort(instances);

return instances;

}

技术实现步骤

实现类： org.springframework.core.io.support.SpringFactoriesLoader

配置资源： META-INF/spring.factories

排序： AnnotationAwareOrderComparator#sort

自定义初始化器

编写类实现ApplicationContextInitializer接口

有两种指定顺序的方法,第一种:类上加注解@Order(Ordered.HIGHEST_PRECEDENCE),第二种则是实http://现Ordered接口

@Order(Ordered.HIGHEST_PRECEDENCE)

public class HelloWorldApplicationContextInitializer

implements ApplicationContextInitializer {

@Override

public void initialize(C applicationContext) {

System.out.println("ConfigurableApplicationContext.id = "+ applicationContext.getId());

}

}

public class AfterHelloWorldApplicationContextInitializer implements ApplicationContextInitializer, Ordered {

@Override

public void initialize(ConfigurableApplicationContext applicationContext) {

System.out.println("After application.id = " + applicationContext.getId());

}

@Override

public int getOrder() {

return Ordered.LOWEST_PRECEDENCE;

}

}

在spring.properties中配置

# ApplicationContextInitializer

org.springframework.context.ApplicationContextInitializer=\

com.imooc.diveinspringboot.context.AfterHelloWorldApplicationContextInitializer,\

com.imooc.diveinspringboot.context.HelloWorldApplicationContextInitializer

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