SpringBoot启动跟踪

程序启动入口

@SpringBootApplication
public class Chapter001Application {

    public static void main(String[] args) {
        SpringApplication.run(Chapter001Application.class, args);
    }
}

调试跟踪

执行初始化方法

/**
     * Create a new {@link SpringApplication} instance. The application context will load
     * beans from the specified sources (see {@link SpringApplication class-level}
     * documentation for details. The instance can be customized before calling
     * {@link #run(String...)}.
     * @param sources the bean sources
     * @see #run(Object, String[])
     * @see #SpringApplication(ResourceLoader, Object...)
     */
    public SpringApplication(Object... sources) {
        initialize(sources);
    }

初始化方法

 applicationContext和applicationListener方法详情

/**
     * Sets the {@link ApplicationContextInitializer} that will be applied to the Spring
     * {@link ApplicationContext}.
     * @param initializers the initializers to set
     */
    public void setInitializers(
            Collection<? extends ApplicationContextInitializer<?>> initializers) {
        this.initializers = new ArrayList<ApplicationContextInitializer<?>>();
        this.initializers.addAll(initializers);
    }

ApplicationContextInitializer初始化applicationContext

/**
     * Sets the {@link ApplicationListener}s that will be applied to the SpringApplication
     * and registered with the {@link ApplicationContext}.
     * @param listeners the listeners to set
     */
    public void setListeners(Collection<? extends ApplicationListener<?>> listeners) {
        this.listeners = new ArrayList<ApplicationListener<?>>();
        this.listeners.addAll(listeners);
    }

注册listener到apllicationContext

applicationContext和applicationlistener初始化都是通过getSpringFactoriesInstances实现的，我们一探究竟

private <T> Collection<? extends T> getSpringFactoriesInstances(Class<T> type) {
        return getSpringFactoriesInstances(type, new Class<?>[] {});
    }

    private <T> Collection<? extends T> getSpringFactoriesInstances(Class<T> type,
            Class<?>[] parameterTypes, Object... args) {
        ClassLoader classLoader = Thread.currentThread().getContextClassLoader();
        // Use names and ensure unique to protect against duplicates
        Set<String> names = new LinkedHashSet<String>(
                SpringFactoriesLoader.loadFactoryNames(type, classLoader));
        List<T> instances = createSpringFactoriesInstances(type, parameterTypes,
                classLoader, args, names);
        AnnotationAwareOrderComparator.sort(instances);
        return instances;
    }

找到了关键节点spring.factories文件,我们查看spring boot下的这个文件看看情况

通过spring.factories文件拿到一系列的Context和Listener之后 执行run方法

run方法会从spring.factories文件中获取到run listener,然后在spring boot 执行到各个阶段时执行Listener事件和Context事件

 最后的run方法如下

了解启动流程，方便优化,下边是网友遇到的问题以及优化方案

https://segmentfault.com/a/1190000004252885