spring启动流程

Spring启动流程

随着springboot的功能越来越强大，我们逐渐忘记了spring，但是每当遇到问题时缺无从下手，
我们在享受springboot给我们带来的便利的同时更应该了解其底层原理，知其然更要知其所以然，下面我们一起进入spring的世界探索吧

Spring启动

我们从springboot的入口(不使用springboot的方式放在后面文章讲解)来看spring是如何被启动的
我们都有启动类如下

AttachCode

@SpringBootApplication
public class Main {

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

我们先来看下SpringApplication.run(Main.class, args);我们今天的主要内容不是springboot，所以我们一路跟踪到spring的refesh方法

AttachCode

   public static ConfigurableApplicationContext run(Class<?>[] primarySources, String[] args) {
        return (new SpringApplication(primarySources)).run(args);
    }

AttachCode

public void refresh(){
//省略部分代码
this.refreshContext(context);
//省略部分代码
}

AttachCode

    private void refreshContext(ConfigurableApplicationContext context) {
        if (this.registerShutdownHook) {
            shutdownHook.registerApplicationContext(context);
        }

        this.refresh(context);
    }

今天的主角AttachCode

@Override
	public void refresh() throws BeansException, IllegalStateException {
		synchronized (this.startupShutdownMonitor) {
			StartupStep contextRefresh = this.applicationStartup.start("spring.context.refresh");

			// Prepare this context for refreshing.
			prepareRefresh();

			// Tell the subclass to refresh the internal bean factory.
			ConfigurableListableBeanFactory beanFactory = obtainFreshBeanFactory();

			// Prepare the bean factory for use in this context.
			prepareBeanFactory(beanFactory);

			try {
				// Allows post-processing of the bean factory in context subclasses.
				postProcessBeanFactory(beanFactory);

				StartupStep beanPostProcess = this.applicationStartup.start("spring.context.beans.post-process");
				// Invoke factory processors registered as beans in the context.
				invokeBeanFactoryPostProcessors(beanFactory);
				// Register bean processors that intercept bean creation.
				registerBeanPostProcessors(beanFactory);
				beanPostProcess.end();

				// Initialize message source for this context.
				initMessageSource();

				// Initialize event multicaster for this context.
				initApplicationEventMulticaster();

				// Initialize other special beans in specific context subclasses.
				onRefresh();

				// Check for listener beans and register them.
				registerListeners();

				// Instantiate all remaining (non-lazy-init) singletons.
				finishBeanFactoryInitialization(beanFactory);

				// Last step: publish corresponding event.
				finishRefresh();
			}

			catch (BeansException ex) {
				if (logger.isWarnEnabled()) {
					logger.warn("Exception encountered during context initialization - " +
							"cancelling refresh attempt: " + ex);
				}

				// Destroy already created singletons to avoid dangling resources.
				destroyBeans();

				// Reset 'active' flag.
				cancelRefresh(ex);

				// Propagate exception to caller.
				throw ex;
			}

			finally {
				// Reset common introspection caches in Spring's core, since we
				// might not ever need metadata for singleton beans anymore...
				resetCommonCaches();
				contextRefresh.end();
			}
		}
	}

今天我们先到这里

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