通过ClassPathXmlApplicationContext源码解读Spring启动过程

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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

20191123100141\_1.png

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<>();
        }

20191123100141\_2.png

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()


来源:http://ddrv.cn/a/88268

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