Spring IOC容器启动流程分析（一）

项目通过maven方式构建，引入jar包：

    org.springframework
    spring-context
    5.3.10

目前5.3.10为Spring framework的最新稳定版本。通过引入spring-context，maven为自动帮我们引入其它相关jar包：spring-core、spring-beans、spring-expression、spring-aop

public class TestBean {
    private String name;

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }
}

public class Main {
    public static void main(String[] args) {
        ClassPathXmlApplicationContext context = new ClassPathXmlApplicationContext("spring-benas.xml");
        TestBean testBean = context.getBean("testBean", TestBean.class);
    }
}

在main方法中加入断点，进行debug，开始分析容器启动流程

	public ClassPathXmlApplicationContext(
			String[] configLocations, boolean refresh, @Nullable ApplicationContext parent)
			throws BeansException {

		super(parent); 
		setConfigLocations(configLocations);
		if (refresh) {
			refresh();
		}
	}

super(parent) 最终会调用到AbstractApplicationContext的构造方法，创建一个新的应用上下文

	
	public AbstractApplicationContext(@Nullable ApplicationContext parent) {
		this();
		setParent(parent);
	}

由于入参parent为空，所以实际只需要关注this()方法就可以了，即当前类的无参构造函数

	
	public AbstractApplicationContext() {
		this.resourcePatternResolver = getResourcePatternResolver();
	}

获取ResourcePatternResolver

	
	public void setConfigLocations(@Nullable String... locations) {
		if (locations != null) {
			Assert.noNullElements(locations, "Config locations must not be null");
			this.configLocations = new String[locations.length];
			for (int i = 0; i < locations.length; i++) {
				this.configLocations[i] = resolvePath(locations[i]).trim();
			}
		}
		else {
			this.configLocations = null;
		}
	}

其中locations即我们传入的配置文件

refresh()方法是Spring启动最重要的方法

	@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();
			}
		}
	}

startupShutdownMonitor作为锁对象，在refresh和destroy时使用，其创建过程在super()中完成

	
	private final Object startupShutdownMonitor = new Object();

1、prepareRefresh
2、obtainFreshBeanFactory() 
3、prepareBeanFactory(beanFactory);
4、postProcessBeanFactory(beanFactory);
5、this.applicationStartup.start("spring.context.beans.post-process");
6、invokeBeanFactoryPostProcessors(beanFactory);
7、registerBeanPostProcessors(beanFactory);
8、beanPostProcess.end();
9、initMessageSource(); 完成国际化操作
10、initApplicationEventMulticaster();
11、onRefresh();
12、registerListeners(); 注册监听器
13、finishBeanFactoryInitialization(beanFactory);
14、finishRefresh();