通过ClassPathXmlApplicationContext源码解读Spring启动过程

川长思鸟来 2022-05-15 08:18 240阅读 0赞

# 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

*  通过ClassPathXmlApplicationContext源码解读Spring启动过程
    
     *  类关系
     *  入口函数
     *  解读refresh方法
        
         *  prepareRefresh()
         *  ConfigurableListableBeanFactory beanFactory = obtainFreshBeanFactory()
         *  prepareBeanFactory(beanFactory)
         *  postProcessBeanFactory(beanFactory)
         *  invokeBeanFactoryPostProcessors(beanFactory)
         *  registerBeanPostProcessors(beanFactory)
         *  initMessageSource()
         *  initApplicationEventMulticaster()
         *  onRefresh()
         *  registerListeners()
         *  finishBeanFactoryInitialization(beanFactory)
         *  finishRefresh()
         *  destroyBeans()
         *  cancelRefresh(ex)
         *  resetCommonCaches()

## 类关系 ##

![这里写图片描述][70]

## 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<>();
        }

![这里写图片描述][70 1]

### `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()` ###