Spring 源码分析之AbstractApplicationContext源码分析

Love The Way You Lie 2022-01-11 01:09 626阅读 0赞

首先我觉得分析ApplicationContext必须从它的实现类开始进行分析，AbstractApplicationContext我觉得是一个不错的选择，那我们就从这里开始逐一分析吧，首先我自己手画了一张图，作为索引吧，其中蓝色的为类，紫色的为接口，箭头 指向的方向是父类或者父接口。

![567748-20190503164841102-1654702530.png][]

因为里面接口和方法过多，所以不做展示，下面具体来进行代码分析。首先我们来看看这句话，MESSAGE\_SOURCE\_BEAN\_NAME。

public static final String MESSAGE_SOURCE_BEAN_NAME = "messageSource";

它这句话翻译成中文就是消息资源的bean的一个name,我们暂时把它看成一个普通的beanName,我们来看看有哪些地方引用到了这个属性，首先在initMessageSource方法里面有引用到，我把这些地方标红显示了。

protected void initMessageSource() {
    		ConfigurableListableBeanFactory beanFactory = getBeanFactory();
    		if (beanFactory.containsLocalBean(MESSAGE_SOURCE_BEAN_NAME)) {
    			this.messageSource = beanFactory.getBean(MESSAGE_SOURCE_BEAN_NAME, MessageSource.class);
    			// Make MessageSource aware of parent MessageSource.
    			if (this.parent != null && this.messageSource instanceof HierarchicalMessageSource) {
    				HierarchicalMessageSource hms = (HierarchicalMessageSource) this.messageSource;
    				if (hms.getParentMessageSource() == null) {
    					// Only set parent context as parent MessageSource if no parent MessageSource
    					// registered already.
    					hms.setParentMessageSource(getInternalParentMessageSource());
    				}
    			}
    			if (logger.isTraceEnabled()) {
    				logger.trace("Using MessageSource [" + this.messageSource + "]");
    			}
    		}
    		else {
    			// Use empty MessageSource to be able to accept getMessage calls.
    			DelegatingMessageSource dms = new DelegatingMessageSource();
    			dms.setParentMessageSource(getInternalParentMessageSource());
    			this.messageSource = dms;
    			beanFactory.registerSingleton(MESSAGE_SOURCE_BEAN_NAME, this.messageSource);
    			if (logger.isTraceEnabled()) {
    				logger.trace("No '" + MESSAGE_SOURCE_BEAN_NAME + "' bean, using [" + this.messageSource + "]");
    			}
    		}
    	}

还有一个显示的地方就是在StaticApplicationContext类中的构造器当中有使用到。下面是StaticApplicationContext的类结构图：

![567748-20190503170125184-597344608.png][]

public StaticApplicationContext(@Nullable ApplicationContext parent) throws BeansException {
    		super(parent);
    
    		// Initialize and register a StaticMessageSource.
    		this.staticMessageSource = new StaticMessageSource();
    		getBeanFactory().registerSingleton(MESSAGE_SOURCE_BEAN_NAME, this.staticMessageSource);
    	}

我们下面再来看一下AbstractApplicationContext这个类的一些Fields,并且来理清一下对象和对象之间的依赖关系，首先是parent -ApplicationContext，我们找到是一个叫做getParent()的方法对这个私有的属性进行了调用，然后又发现了getParentBeanFactory方法也对其进行了间接调用，因为BeanFactory是ApplicationContext的父接口，如下图：

![567748-20190503171504665-1660815696.png][]

private ApplicationContext parent;

public ApplicationContext getParent() {
        
       return this.parent;
    }

public BeanFactory getParentBeanFactory() {
        
       return getParent();
    }

在这个类中还有一个属性是environment,这个environment在这里也有getter和setter方法，唯一需要注意的是如果调用getEnvironment()方法在environment为空的情况下会创建一个StandardEnvironment对象。

private ConfigurableEnvironment environment;

public ConfigurableEnvironment getEnvironment() {
        
       if (this.environment == null) {
        
          this.environment = createEnvironment();
       }
       return this.environment;
    }

StandardEnvironment类继承了抽象的AbstractEnvironment，它的类结构图如下所示：

![567748-20190503172219826-1807451631.png][]

还有一个比较重要的属性就是beanFactoryPostProcessors，这事一个ArrayList的数组,Doc当中给出的解释是当onRefresh的时候有用到。我找到了3个方法引用到了这个属性，下面都已标红。

private final List<BeanFactoryPostProcessor> beanFactoryPostProcessors = new ArrayList<>();

public void addBeanFactoryPostProcessor(BeanFactoryPostProcessor postProcessor) {
        
       Assert.notNull(postProcessor, "BeanFactoryPostProcessor must not be null");
       this.beanFactoryPostProcessors.add(postProcessor);
    }

public List<BeanFactoryPostProcessor> getBeanFactoryPostProcessors() {
        
       return this.beanFactoryPostProcessors;
    }

protected void invokeBeanFactoryPostProcessors(ConfigurableListableBeanFactory beanFactory) {
        
       PostProcessorRegistrationDelegate.invokeBeanFactoryPostProcessors(beanFactory, getBeanFactoryPostProcessors());
    
       // Detect a LoadTimeWeaver and prepare for weaving, if found in the meantime
       // (e.g. through an @Bean method registered by ConfigurationClassPostProcessor)
       if (beanFactory.getTempClassLoader() == null && beanFactory.containsBean(LOAD_TIME_WEAVER_BEAN_NAME)) {
        
          beanFactory.addBeanPostProcessor(new LoadTimeWeaverAwareProcessor(beanFactory));
          beanFactory.setTempClassLoader(new ContextTypeMatchClassLoader(beanFactory.getBeanClassLoader()));
       }
    }

往下面看还有一个属性active,它是线程安全的，用到了CAS技术。它常常和closed这个属性一起使用，我们发现，在如下3个地方有组合引用，我已用相应的颜色标识出来。

*  prepareRefresh
 *  doClose
 *  assertBeanFactoryActive

private final AtomicBoolean active = new AtomicBoolean();

private final AtomicBoolean closed = new AtomicBoolean();

protected void prepareRefresh() {
        
       // Switch to active.
       this.startupDate = System.currentTimeMillis();
       this.closed.set(false);
       this.active.set(true);
       ....................
       ....................
    }

protected void doClose() {
        
       // Check whether an actual close attempt is necessary...
       if (this.active.get() && this.closed.compareAndSet(false, true)) {
        
          if (logger.isDebugEnabled()) {
        
             logger.debug("Closing " + this);
          }
        ........................
        ........................

//Switch to inactive.
       this.active.set(false);

}

protected void assertBeanFactoryActive() {
        
       if (!this.active.get()) {
        
          if (this.closed.get()) {
        
             throw new IllegalStateException(getDisplayName() + " has been closed already");
          }
          else {
        
             throw new IllegalStateException(getDisplayName() + " has not been refreshed yet");
          }
       }
    }

我们继续往下看，有一个startupShutdownMonitor的属性，字面意思上面理解就是启动关闭监视器，属性在这个类当中的命名表示了它所发挥的作用，我们来看一下有哪些方法引用到了这个属性。大家不知道发现没有，还有一个“很像”的属性在这里就是shutdownHook,这个和startupShutdownMonitor是配合在一起使用的。shudownHook在这里是一个线程类型的属性。

private final Object startupShutdownMonitor = new Object();

private Thread shutdownHook;

public void refresh() throws BeansException, IllegalStateException {
         
       synchronized (this.startupShutdownMonitor) {......

}......
    }

public void registerShutdownHook() {
        
       if (this.shutdownHook == null) {
        
          // No shutdown hook registered yet.
          this.shutdownHook = new Thread() {
        
             @Override
             public void run() {
        
                synchronized (startupShutdownMonitor) {
        
                   doClose();
                }
             }
          };
          Runtime.getRuntime().addShutdownHook(this.shutdownHook);
       }
    }

public void close() {
        
       synchronized (this.startupShutdownMonitor) {
        
          doClose();
          // If we registered a JVM shutdown hook, we don't need it anymore now:
          // We've already explicitly closed the context.
          if (this.shutdownHook != null) {
        
             try {
        
                Runtime.getRuntime().removeShutdownHook(this.shutdownHook);
             }
             catch (IllegalStateException ex) {
        
                // ignore - VM is already shutting down
             }
          }
       }
    }

既然shutdownHook和startupShutdownMonitor一起使用，那么它们之间的关系我们得分析一下,hook顾名思义钩子，说简单点这个就是一个钩子，也算是一个扩展点。我们来仔细分析一下它的几个方法，首先是registerShutdownHook方法：这个方法有一句话特别重要，就是Runtime.getRuntime().addShutdownHook(this.shutdownHook);它实际上在系统层面上把钩子线程添加到了JVM虚拟机。在钩子运行的时候，就会执行doClose方法关闭并销毁applicationContext。需要注意的一点是明白registerShutdownHook方法和close方法的不同点，在close方法中如果发现已经调用registerShutdownHook在JVM层面上注册了钩子，那么就调用Runtime.getRuntime().removeShutdownHook(this.shutdownHook)移除此钩子，另外这个close的实现来自于closable接口的父接口AutoClosable接口方法，而registerShutdownHook则在PropertyResolver当中被定义。

public void registerShutdownHook() {
    		if (this.shutdownHook == null) {
    			// No shutdown hook registered yet.
    			this.shutdownHook = new Thread() {
    				@Override
    				public void run() {
    					synchronized (startupShutdownMonitor) {
    						doClose();
    					}
    				}
    			};
    			Runtime.getRuntime().addShutdownHook(this.shutdownHook);
    		}
    	}

时间不早了，今天就写到这里吧。

转载于:https://www.cnblogs.com/kmsfan/p/10805845.html

[567748-20190503164841102-1654702530.png]: /images/20220110/ab36e0c71e724a318e8bab476bc44fa8.png
[567748-20190503170125184-597344608.png]: /images/20220110/545ac611f96042ffa0e2d835f5c8a74f.png
[567748-20190503171504665-1660815696.png]: /images/20220110/9c6333aaf3ad4198aa35f0e14f2f97f2.png
[567748-20190503172219826-1807451631.png]: /images/20220110/82d2ae22890e4e3baa9111a2bd63580b.png