springmvc5中设计模式

用了5种设计模式
组合模式
责任链模式
适配器模式
策略模式

组合模式

WebMvcConfigurerComposite体现了组合模式

树枝节点用Composite结尾，里面包含了树叶节点，树枝和树叶都实现了相同的抽象类或接口WebMvcConfigurer

class WebMvcConfigurerComposite implements WebMvcConfigurer {private final List<WebMvcConfigurer> delegates = new ArrayList();WebMvcConfigurerComposite() {}public void addWebMvcConfigurers(List<WebMvcConfigurer> configurers) {if(!CollectionUtils.isEmpty(configurers)) {this.delegates.addAll(configurers);}}
...
}

责任链模式

DispatcherServlet核心方法doDispatch体现了责任链模式
request是请求，所有入参包含request的方法，都是责任链的体现

protected void doDispatch(HttpServletRequest request, HttpServletResponse response) throws Exception {HttpServletRequest processedRequest = request;HandlerExecutionChain mappedHandler = null;boolean multipartRequestParsed = false;WebAsyncManager asyncManager = WebAsyncUtils.getAsyncManager(request);try {ModelAndView mv = null;Exception dispatchException = null;try {processedRequest = checkMultipart(request);multipartRequestParsed = (processedRequest != request);// 获取该请求的handler，每个handler实为HandlerExecutionChain，它为一个处理链，负责处理整个请求mappedHandler = getHandler(processedRequest);if (mappedHandler == null || mappedHandler.getHandler() == null) {noHandlerFound(processedRequest, response);return;}HandlerAdapter ha = getHandlerAdapter(mappedHandler.getHandler());String method = request.getMethod();boolean isGet = "GET".equals(method);if (isGet || "HEAD".equals(method)) {long lastModified = ha.getLastModified(request, mappedHandler.getHandler());if (logger.isDebugEnabled()) {logger.debug("Last-Modified value for [" + getRequestUri(request) + "] is: " + lastModified);}if (new ServletWebRequest(request, response).checkNotModified(lastModified) && isGet) {return;}}// 责任链执行预处理方法，实则是将请求交给注册的请求拦截器执行if (!mappedHandler.applyPreHandle(processedRequest, response)) {return;}// 实际的执行逻辑的部分，也就是你加了@RequestMapping注解的方法mv = ha.handle(processedRequest, response, mappedHandler.getHandler());if (asyncManager.isConcurrentHandlingStarted()) {return;}applyDefaultViewName(processedRequest, mv);// 责任链执行后处理方法，实则是将请求交给注册的请求拦截器执行mappedHandler.applyPostHandle(processedRequest, response, mv);}catch (Exception ex) {dispatchException = ex;}catch (Throwable err) {dispatchException = new NestedServletException("Handler dispatch failed", err);}// 处理返回的结果，触发责任链上注册的拦截器的AfterCompletion方法，其中也用到了HandlerExecutionChain注册的handler来处理错误结果processDispatchResult(processedRequest, response, mappedHandler, mv, dispatchException);}catch (Exception ex) {// 触发责任链上注册的拦截器的AfterCompletion方法triggerAfterCompletion(processedRequest, response, mappedHandler, ex);}catch (Throwable err) {triggerAfterCompletion(processedRequest, response, mappedHandler,new NestedServletException("Handler processing failed", err));}finally {if (asyncManager.isConcurrentHandlingStarted()) {if (mappedHandler != null) {mappedHandler.applyAfterConcurrentHandlingStarted(processedRequest, response);}}else {if (multipartRequestParsed) {cleanupMultipart(processedRequest);}}}}

适配器模式

适配器模式将某个类的接口转换成客户端期望的另一个接口表示，主的目的是兼容性，让原本因接口不匹配不能一起工作的两个类可以协同工作.它主要分为三类:类适配器模式、对象的适配器模式、接口的适配器模式.
适配器类以Adapter结尾，

但是HandlerAdapter 是接口，不是适配器类

public interface HandlerAdapter {/*** 判断此handler是否是此HandlerAdapter支持的类型，每种HandlerAdapter只支持一种类型的handler*/boolean supports(Object handler);/*** 使用所给的handler处理请求*/ModelAndView handle(HttpServletRequest request, HttpServletResponse response, Object handler) throws Exception;long getLastModified(HttpServletRequest request, Object handler);}

HandlerAdapter有五个实现类，其中继承自AbstractHandlerMethodAdapter的RequestMappingHandlerAdapter就是springMVC中处理请求最重要的类之一。

public abstract class AbstractHandlerMethodAdapter extends WebContentGenerator implements HandlerAdapter, Ordered {private int order = Ordered.LOWEST_PRECEDENCE;public AbstractHandlerMethodAdapter() {// no restriction of HTTP methods by defaultsuper(false);}public void setOrder(int order) {this.order = order;}@Overridepublic int getOrder() {return this.order;}/*** 用instanceof判断此handler是否是HandlerMethod类型*/@Overridepublic final boolean supports(Object handler) {return (handler instanceof HandlerMethod && supportsInternal((HandlerMethod) handler));}/*** 判断是否支持此HandlerMethod*/protected abstract boolean supportsInternal(HandlerMethod handlerMethod);/*** 将handler强转为HandlerMethod传入handleInternal方法*/@Overridepublic final ModelAndView handle(HttpServletRequest request, HttpServletResponse response, Object handler)throws Exception {return handleInternal(request, response, (HandlerMethod) handler);}/*** 实际的处理方法，由子类实现，由所给HandlerMethod处理请求*/protected abstract ModelAndView handleInternal(HttpServletRequest request,HttpServletResponse response, HandlerMethod handlerMethod) throws Exception;@Overridepublic final long getLastModified(HttpServletRequest request, Object handler) {return getLastModifiedInternal(request, (HandlerMethod) handler);}protected abstract long getLastModifiedInternal(HttpServletRequest request, HandlerMethod handlerMethod);}

策略模式

策略模式是指对一系列的算法定义，并将每一个算法封装起来，而且使它们还可以相互替换。策略模式让算法独立于使用它的客户而独立变化。
使用策略模式有时候可以让我们的编码从繁琐难维护的if-else中解放出来。

决定request的media types时也用到了策略模式。其中的ContentNegotiationManager是最核心的一个类

策略接口

@FunctionalInterface
public interface ContentNegotiationStrategy {List<MediaType> resolveMediaTypes(NativeWebRequest var1) throws HttpMediaTypeNotAcceptableException;
}

很多实现类，实现具体策略

ContentNegotiationManager处理类也可以实现策略接口

public class ContentNegotiationManager implements ContentNegotiationStrategy, MediaTypeFileExtensionResolver {private static final List<MediaType> MEDIA_TYPE_ALL;private final List<ContentNegotiationStrategy> strategies;private final Set<MediaTypeFileExtensionResolver> resolvers;public ContentNegotiationManager(ContentNegotiationStrategy... strategies) {this((Collection)Arrays.asList(strategies));}public ContentNegotiationManager(Collection<ContentNegotiationStrategy> strategies) {this.strategies = new ArrayList();this.resolvers = new LinkedHashSet();Assert.notEmpty(strategies, "At least one ContentNegotiationStrategy is expected");this.strategies.addAll(strategies);Iterator var2 = this.strategies.iterator();while(var2.hasNext()) {ContentNegotiationStrategy strategy = (ContentNegotiationStrategy)var2.next();if(strategy instanceof MediaTypeFileExtensionResolver) {this.resolvers.add((MediaTypeFileExtensionResolver)strategy);}}}public ContentNegotiationManager() {this(new ContentNegotiationStrategy[]{new HeaderContentNegotiationStrategy()});}public List<ContentNegotiationStrategy> getStrategies() {return this.strategies;}public List<MediaType> resolveMediaTypes(NativeWebRequest request) throws HttpMediaTypeNotAcceptableException {Iterator var2 = this.strategies.iterator();List mediaTypes;do {if(!var2.hasNext()) {return Collections.emptyList();}ContentNegotiationStrategy strategy = (ContentNegotiationStrategy)var2.next();mediaTypes = strategy.resolveMediaTypes(request);} while(mediaTypes.isEmpty() || mediaTypes.equals(MEDIA_TYPE_ALL));return mediaTypes;}