通过ClassPathXmlApplicationContext源码解读Spring启动过程

2019年3月19日 290次阅读 来源: Spring Cloud

通过ClassPathXmlApplicationContext源码解读Spring启动过程

@(Spring)[Spring][源码]

注：本次分析基于spring-context-5.1.0.RC1.jar

类关系

《通过ClassPathXmlApplicationContext源码解读Spring启动过程》

入口函数

通过ClassPathXmlApplicationContext类构造方法启动父类AbstractApplicationContext的函数refresh方法

/** * Create a new ClassPathXmlApplicationContext, loading the definitions * from the given XML file and automatically refreshing the context. * @param configLocation resource location * @throws BeansException if context creation failed */
public ClassPathXmlApplicationContext(String configLocation) throws BeansException {
    this(new String[] {configLocation}, true, null);
}
/** * Create a new ClassPathXmlApplicationContext with the given parent, * loading the definitions from the given XML files. * @param configLocations array of resource locations * @param refresh whether to automatically refresh the context, * loading all bean definitions and creating all singletons. * Alternatively, call refresh manually after further configuring the context. * @param parent the parent context * @throws BeansException if context creation failed * @see #refresh() */
public ClassPathXmlApplicationContext(
        String[] configLocations, boolean refresh, @Nullable ApplicationContext parent)
        throws BeansException {
    super(parent);
    setConfigLocations(configLocations);
    if (refresh) {
        refresh();
    }
}
@Override
public void refresh() throws BeansException, IllegalStateException {
    synchronized (this.startupShutdownMonitor) {
        // 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);

            // Invoke factory processors registered as beans in the context.
            invokeBeanFactoryPostProcessors(beanFactory);

            // Register bean processors that intercept bean creation.
            registerBeanPostProcessors(beanFactory);

            // 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();
        }
    }
}

解读refresh方法

refresh方法第一行是对startupShutdownMonitor进行了加锁处理，使得refresh方法线程同步，然后执行下面一系列的方法，这里先初步了解一下每个方法的作用，后面再对每一个方法进行详细解析

prepareRefresh()

主要有两段逻辑， 涉及重要的类Environment\AbstractEnvironment
1.1 initPropertySources方法是一个protected的空方法，留给子类实现的
1.2 getEnvironment().validateRequiredProperties()创建了spring的环境参数组件，并验证必备参数

通过System.getProperties()获取JVM相关参数，System.getenv()程序运行的系统、硬件及环境变量相关参数
获取后的参数放入AbstractEnvironment类的成员变量propertySources中

    /** * Prepare this context for refreshing, setting its startup date and * active flag as well as performing any initialization of property sources. */
    protected void prepareRefresh() {
        this.startupDate = System.currentTimeMillis();
        this.closed.set(false);
        this.active.set(true);

        if (logger.isDebugEnabled()) {
            if (logger.isTraceEnabled()) {
                logger.trace("Refreshing " + this);
            }
            else {
                logger.debug("Refreshing " + getDisplayName());
            }
        }

        // Initialize any placeholder property sources in the context environment
        initPropertySources();

        // Validate that all properties marked as required are resolvable
        // see ConfigurablePropertyResolver#setRequiredProperties
        getEnvironment().validateRequiredProperties();

        // Allow for the collection of early ApplicationEvents,
        // to be published once the multicaster is available...
        this.earlyApplicationEvents = new LinkedHashSet<>();
    }

《通过ClassPathXmlApplicationContext源码解读Spring启动过程》

ConfigurableListableBeanFactory beanFactory = obtainFreshBeanFactory()

解析项目配置的 application.xml、xxx.xml 定义的import、bean、resource、profile等等，得到一个bean工厂对象

prepareBeanFactory(beanFactory)

对bean工厂做一些初始化处理

postProcessBeanFactory(beanFactory)

spring提供的扩展点，可以通过继承ClassPathXmlApplicationContext来重写该方法

invokeBeanFactoryPostProcessors(beanFactory)

registerBeanPostProcessors(beanFactory)

initMessageSource()

initApplicationEventMulticaster()

onRefresh()

registerListeners()

finishBeanFactoryInitialization(beanFactory)

finishRefresh()

destroyBeans()

cancelRefresh(ex)

resetCommonCaches()

    原文作者：Spring Cloud
    原文地址: https://blog.csdn.net/tongsh6/article/details/82114364
    本文转自网络文章，转载此文章仅为分享知识，如有侵权，请联系博主进行删除。
点赞