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 ApplicationContextInitializer 实现类，并排序对象集合。

关键方法

private <T> Collection<T> getSpringFactoriesInstances(Class<T> type,Class<?>[] parameterTypes, Object... args) {ClassLoader classLoader = Thread.currentThread().getContextClassLoader();// Use names and ensure unique to protect against duplicatesSet<String> names = new LinkedHashSet<>(SpringFactoriesLoader.loadFactoryNames(type, classLoader));List<T> 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),第二种则是实现Ordered接口

@Order(Ordered.HIGHEST_PRECEDENCE)public class HelloWorldApplicationContextInitializer<C extends ConfigurableApplicationContext> implements ApplicationContextInitializer<C> { @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

# ApplicationContextInitializerorg.springframework.context.ApplicationContextInitializer=com.imooc.diveinspringboot.context.AfterHelloWorldApplicationContextInitializer,com.imooc.diveinspringboot.context.HelloWorldApplicationContextInitializer

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