SpringBoot 启动源码解析系列四：实例化 ApplicationListener

2018-01-02

SpringApplication initialize 方法：

private void initialize(Object[] sources) {
    if (sources != null && sources.length > 0) {
        this.sources.addAll(Arrays.asList(sources));
    }

    this.webEnvironment = this.deduceWebEnvironment();
    this.setInitializers(this.getSpringFactoriesInstances(ApplicationContextInitializer.class));
    this.setListeners(this.getSpringFactoriesInstances(ApplicationListener.class));
    this.mainApplicationClass = this.deduceMainApplicationClass();
}

setListeners 方法即找到 ApplicationListener 类并实例化

ApplicationListener 是 Spring 框架中事件监听器接口，即 SpringApplicationRunListener 发布通知事件时，由 ApplicationListener 负责接收。具体可以参考 Spring 事件监听机制。

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public interface ApplicationListener<E extends ApplicationEvent> extends EventListener {
    void onApplicationEvent(E var1);
}

ApplicationListener 在 SpringBoot 中包含两块：

spring-boot-x.x.x.RELEASE.jar/META-INF/spring.factories中：

# Application Listeners
org.springframework.context.ApplicationListener=\
org.springframework.boot.ClearCachesApplicationListener,\
org.springframework.boot.builder.ParentContextCloserApplicationListener,\
org.springframework.boot.context.FileEncodingApplicationListener,\
org.springframework.boot.context.config.AnsiOutputApplicationListener,\
org.springframework.boot.context.config.ConfigFileApplicationListener,\
org.springframework.boot.context.config.DelegatingApplicationListener,\
org.springframework.boot.liquibase.LiquibaseServiceLocatorApplicationListener,\
org.springframework.boot.logging.ClasspathLoggingApplicationListener,\
org.springframework.boot.logging.LoggingApplicationListener

spring-boot-autoconfigure-x.x.x.RELEASE.jar/META-INF/spring.factories中：

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# Application Listeners
org.springframework.context.ApplicationListener=\
org.springframework.boot.autoconfigure.BackgroundPreinitializer