springmvc5中设计模式

痛定思痛。 2022-02-21 11:38 183阅读 0赞

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);
    
    }

![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L21pbmd3dWxpcG8_size_16_color_FFFFFF_t_70]  
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 default
            super(false);
        }
    
        public void setOrder(int order) {
            this.order = order;
        }
    
        @Override
        public int getOrder() {
            return this.order;
        }
    
    
        /**
         * 用instanceof判断此handler是否是HandlerMethod类型
         */
        @Override
        public 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
         */
        @Override
        public 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;
    
        @Override
        public 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  
![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L21pbmd3dWxpcG8_size_16_color_FFFFFF_t_70 1]

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;
        }

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