spring-context

1、实用的Bean工厂ApplicationContext

ApplicationContext的中文意思是“应用前后关系”，它继承自BeanFactory接口，
除了包含BeanFactory的所有功能之外，在国际化支持、资源访问（如URL和文件）、
事件传播等方面进行了良好的支持

特性

在ApplicationContext接口的众多实现类中，有3个是我们经常用到的（见表1-1），并且使用这3个实现类也基本能满足我们Java EE应用开发中的绝大部分需求。

表1-1 ApplicationContext接口的常用实现类介绍

类 名 称	功 能 描 述
ClassPathXmlApplicationContext	从类路径ClassPath中寻找指定的XML配置文件，找到并装载完成ApplicationContext的实例化工作。例如： //装载单个配置文件实例化ApplicationContext容器 ApplicationContext cxt = new ClassPathXmlApplicationContext(“applicationContext.xml”); //装载多个配置文件实例化ApplicationContext容器 String[] configs = {“bean1.xml”,”bean2.xml”,”bean3.xml”}; ApplicationContext cxt = new ClassPathXmlApplicationContext(configs);
FileSystemXmlApplicationContext	从指定的文件系统路径中寻找指定的XML配置文件，找到并装载完成ApplicationContext的实例化工作。例如： //装载单个配置文件实例化ApplicationContext容器 ApplicationContext cxt = new FileSystemXMLApplicationContext(“beans.xml”); //装载多个配置文件实例化ApplicationContext容器 String[] configs = {“c:/beans1.xml”,”c:/beans2.xml”}; ApplicationContext cxt = new FileSystemXmlApplicationContext(configs);
XmlWebApplicationContext	从Web应用中寻找指定的XML配置文件，找到并装载完成ApplicationContext的实例化工作。这是为Web工程量身定制的，使用WebApplicationContextUtils类的getRequiredWebApplicationContext方法可在JSP与Servlet中取得IoC容器的引用

实现

• ApplicationContext类图
  

---

• 分析：
  

  1.ClassPathXmlApplicationContext

   	public ClassPathXmlApplicationContext(
  	String[] configLocations, boolean refresh, @Nullable ApplicationContext parent) throws BeansException {
  
  	super(parent);
  	setConfigLocations(configLocations);
  	if (refresh) {
  		refresh();
  	}
  }

  • 首先调用setConfigLocations(configLocations)方法
    
    setConfigLocations为AbstractRefreshableConfigApplicationContext中的方法，设置configLocations，将要解析的xml文件名进去

  • 重点在refresh()中，refresh()在AbstractApplicationContext类中，所有解析xml文件和装配bean的动作都发生在这里
    

    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();
    		}
    	}
    }

赏

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