BeanFactory，从xml或者注解加载BeanDefinition，然后实例化对象，其中AbstractAutowiredCapableBeanFactory实现了主要的逻辑
spring创建的bean默认为singleton
比如说Springmvc的HandlerInterceptorAdapter就是个接口适配器，实现了AsyncHandlerInterceptor(HandlerInterceptor的子类)，ThemeChangeInterceptor继承至HandlerInterceptorAdapter，只需要重写关注的方法即可，不相关的方法完全可以忽略。
public abstract class HandlerInterceptorAdapter implements AsyncHandlerInterceptor { @Override public boolean preHandle(HttpServletRequest request, HttpServletResponse response, Object handler) throws Exception { return true; } @Override public void postHandle( HttpServletRequest request, HttpServletResponse response, Object handler, ModelAndView modelAndView) throws Exception { } @Override public void afterCompletion( HttpServletRequest request, HttpServletResponse response, Object handler, Exception ex) throws Exception { } @Override public void afterConcurrentHandlingStarted( HttpServletRequest request, HttpServletResponse response, Object handler) throws Exception { }}public class ThemeChangeInterceptor extends HandlerInterceptorAdapter { @Override public boolean preHandle(HttpServletRequest request, HttpServletResponse response, Object handler) throws ServletException { // do somethings }}个人认为用得最好的地方莫过于spring-jms的MessagingMessageListenerAdapter，在onMessage中将jsm的Message转换为message模块的Message对象(内部类的LazyResolutionMessage，重写了getPayload、getHeader)，并交给message模块的InvocableHandleMethod，这样一来便可以实现jms与spring message无缝适配对接了，在spring-websocket也是相同的套路
public class MessagingMessageListenerAdapter extends AbstractAdaptableMessageListener { private InvocableHandlerMethod handlerMethod; public void setHandlerMethod(InvocableHandlerMethod handlerMethod) { this.handlerMethod = handlerMethod; } @Override public void onMessage(javax.jms.Message jmsMessage, Session session) throws JMSException { Message<?> message = toMessagingMessage(jmsMessage); if (logger.isDebugEnabled()) { logger.debug("Processing [" + message + "]"); } Object result = invokeHandler(jmsMessage, session, message); if (result != null) { handleResult(result, jmsMessage, session); } else { logger.trace("No result object given - no result to handle"); } } protected Message<?> toMessagingMessage(javax.jms.Message jmsMessage) { try { return (Message<?>) getMessagingMessageConverter().fromMessage(jmsMessage); } catch (JMSException ex) { throw new MessageConversionException("Could not convert JMS message", ex); } } // 忽略部分代码}装饰模式是指在不影响其它类的情况下，动态透明的扩展一个对象的功能，比如TransactionAwareCacheDecorator增加了对事务的支持，在事务提交、回滚的时候分别对Cache的数据进行处理。不过，装饰模式和静态代理还是有区别的，装饰模式只是在调用前后加了些逻辑，但是最终还是需要调用父类或者装饰类；而代理模式是需要or不需要来完成对代理方法的调用，比如AOP可以有选择性地处理某些方法，并不一定会执行代理类的具体方法。
public class TransactionAwareCacheDecorator implements Cache { private final Cache targetCache; @Override public void put(final Object key, final Object value) { if (TransactionSynchronizationManager.isSynchronizationActive()) { TransactionSynchronizationManager.registerSynchronization(new TransactionSynchronizationAdapter() { @Override public void afterCommit() { targetCache.put(key, value); } }); } else { this.targetCache.put(key, value); } } // 忽略部分代码}在spring中我们借助ApplicationListener、ApplicationEventPublisher便可以完成简直的事件通知。当调用ApplicationEventPublisher#publishEvent()时，spring会查找实现了ApplicationListener接口、并且使用了指定泛型的bean，然后调用其onApplicationEvent。下面的代码示范了spring发出ContextRefreshedEvent事件。
ApplicationEventPublisher eventPublisher = xxx;eventPublisher.publishEvent( new ContextRefreshedEvent( applicationContext ) );public class TestListener implements ApplicationListener<ContextRefreshedEvent> { @Override public void onApplicationEvent(ContextRefreshedEvent event) { // invoke after spring context refreshed }}比如SpringMVC的HandlerMethodArgumentResolver接口，使用HandlerMethodArgumentResolverComposite(实现HandlerMethodArgumentResolver接口)，通过遍历内部所有的HandlerMethodArgumentResolver(当然有缓存 机制)，选择support返回true的实例，并把接口的调用交给该实例处理
其实，我们在写业务代码的时候，很多童鞋喜欢用Map保存策略实现类，其实这样并不好，不够灵活，应该像spring这样提供一个support方法，可以支持更加复杂的逻辑判断
public class HandlerMethodArgumentResolverComposite implements HandlerMethodArgumentResolver { protected final Log logger = LogFactory.getLog(getClass()); private final List<HandlerMethodArgumentResolver> argumentResolvers = new LinkedList<HandlerMethodArgumentResolver>(); private final Map<MethodParameter, HandlerMethodArgumentResolver> argumentResolverCache = new ConcurrentHashMap<MethodParameter, HandlerMethodArgumentResolver>(256); @Override public boolean supportsParameter(MethodParameter parameter) { return (getArgumentResolver(parameter) != null); } private HandlerMethodArgumentResolver getArgumentResolver(MethodParameter parameter) { HandlerMethodArgumentResolver result = this.argumentResolverCache.get(parameter); if (result == null) { for (HandlerMethodArgumentResolver methodArgumentResolver : this.argumentResolvers) { if (methodArgumentResolver.supportsParameter(parameter)) { result = methodArgumentResolver; this.argumentResolverCache.put(parameter, result); break; } } } return result; } @Override public Object resolveArgument(MethodParameter parameter, ModelAndViewContainer mavContainer, NativeWebRequest webRequest, WebDataBinderFactory binderFactory) throws Exception { HandlerMethodArgumentResolver resolver = getArgumentResolver(parameter); if (resolver == null) { throw new IllegalArgumentException("Unknown parameter type [" + parameter.getParameterType().getName() + "]"); } return resolver.resolveArgument(parameter, mavContainer, webRequest, binderFactory); }}静态代理在Spring websocket里面非常常见，比如说WebsocketHandlerDecorator，因为它不方便直接操作开发者自定义的WebSocketHandler，因此使用了代理模式。另外，cglib、jdk动态代理在spring中也是非常常见
public class WebSocketHandlerDecorator implements WebSocketHandler { private final WebSocketHandler delegate; public WebSocketHandlerDecorator(WebSocketHandler delegate) { Assert.notNull(delegate, "Delegate must not be null"); this.delegate = delegate; } @Override public void afterConnectionEstablished(WebSocketSession session) throws Exception { this.delegate.afterConnectionEstablished(session); } @Override public void handleMessage(WebSocketSession session, WebSocketMessage<?> message) throws Exception { this.delegate.handleMessage(session, message); } // 省略部分代码}比如SpringMVC的HandlerExecutionChain与HandlerInterceptor，以及ExceptionHandlerResolver
下面是HandlerExecutionChain的部分代码，由DispatcherServlet调用，内部维护了interceptorIndex，用于标记当前调用HandlerInterceptor的位置
public class HandlerExecutionChain { private final Object handler; private HandlerInterceptor[] interceptors; private int interceptorIndex = -1; boolean applyPreHandle(HttpServletRequest request, HttpServletResponse response) throws Exception { HandlerInterceptor[] interceptors = getInterceptors(); if (!ObjectUtils.isEmpty(interceptors)) { for (int i = 0; i < interceptors.length; i++) { HandlerInterceptor interceptor = interceptors[i]; if (!interceptor.preHandle(request, response, this.handler)) { triggerAfterCompletion(request, response, null); return false; } this.interceptorIndex = i; } } return true; } void applyPostHandle(HttpServletRequest request, HttpServletResponse response, ModelAndView mv) throws Exception { HandlerInterceptor[] interceptors = getInterceptors(); if (!ObjectUtils.isEmpty(interceptors)) { for (int i = interceptors.length - 1; i >= 0; i--) { HandlerInterceptor interceptor = interceptors[i]; interceptor.postHandle(request, response, this.handler, mv); } } }}再比如说springMVC对异常的处理，DispatcherServlet会保存所有的HandlerExceptionResolver，当出现异常时，挨个调用HandlerExceptionResolver实例的resolveException方法，直到返回ModelAndView
为了简化对象的创建过程而使用的一种设计模式，比如BeanDefinitionBuilder是为了简化BeanDefinition的创建过程，每次setXXX都会返回BeanDefinitionBuilder实例，方便以链条编码的方式创建BeanDefinitionBuilder
public class BeanDefinitionBuilder { public static BeanDefinitionBuilder genericBeanDefinition(Class<?> beanClass) { BeanDefinitionBuilder builder = new BeanDefinitionBuilder(); builder.beanDefinition = new GenericBeanDefinition(); builder.beanDefinition.setBeanClass(beanClass); return builder; } private AbstractBeanDefinition beanDefinition; public BeanDefinitionBuilder addConstructorArgValue(Object value) { this.beanDefinition.getConstructorArgumentValues().addIndexedArgumentValue( this.constructorArgIndex++, value); return this; } public BeanDefinitionBuilder addPropertyValue(String name, Object value) { this.beanDefinition.getPropertyValues().add(name, value); return this; }}spring中很多地方会这样做，在一个方法里面完成了一小部分逻辑，然后接着调用一个或多个抽象方法，而这个抽象方法需要由子类重写，比如AbstractApplicationContext里面的refresh()、getBeanFactory()等等，这样便可以很好的提高了程序的扩展性
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