mvc静态资源访问之缓存cache-period

客官°小女子只卖身不卖艺 2022-03-27 09:22 203阅读 0赞

cache-period 对静态资源的缓存，这样的话，下次请求就不会再请求服务器，而是利用了浏览器的缓存、从而降低了服务器的压力。  
![2][]  
底层是怎杨处理的？

<mvc:resources mapping="/images/**" location="/images/" cache-period="31556926"/>
        <mvc:resources mapping="/css/**" location="/css/" cache-period="31556926"/>
        <mvc:resources mapping="/js/**" location="/js/" cache-period="31556926"/>

<mvc: 类的均在MvcNamespaceHandler 中定义

public class MvcNamespaceHandler extends NamespaceHandlerSupport { 
        public MvcNamespaceHandler() { 
        }
    
        public void init() { 
            this.registerBeanDefinitionParser("annotation-driven", new AnnotationDrivenBeanDefinitionParser());
            this.registerBeanDefinitionParser("default-servlet-handler", new DefaultServletHandlerBeanDefinitionParser());
            this.registerBeanDefinitionParser("interceptors", new InterceptorsBeanDefinitionParser());
            // 瞅瞅这里
            this.registerBeanDefinitionParser("resources", new ResourcesBeanDefinitionParser());
            this.registerBeanDefinitionParser("view-controller", new ViewControllerBeanDefinitionParser());
            this.registerBeanDefinitionParser("redirect-view-controller", new ViewControllerBeanDefinitionParser());
            this.registerBeanDefinitionParser("status-controller", new ViewControllerBeanDefinitionParser());
            this.registerBeanDefinitionParser("view-resolvers", new ViewResolversBeanDefinitionParser());
            this.registerBeanDefinitionParser("tiles-configurer", new TilesConfigurerBeanDefinitionParser());
            this.registerBeanDefinitionParser("freemarker-configurer", new FreeMarkerConfigurerBeanDefinitionParser());
            this.registerBeanDefinitionParser("velocity-configurer", new VelocityConfigurerBeanDefinitionParser());
            this.registerBeanDefinitionParser("groovy-configurer", new GroovyMarkupConfigurerBeanDefinitionParser());
            this.registerBeanDefinitionParser("script-template-configurer", new ScriptTemplateConfigurerBeanDefinitionParser());
            this.registerBeanDefinitionParser("cors", new CorsBeanDefinitionParser());
        }
    }

我们查看 new ResourcesBeanDefinitionParser（）创建对象

private String registerResourceHandler(ParserContext parserContext, Element element, Object source) { 
            String locationAttr = element.getAttribute("location");
            if (!StringUtils.hasText(locationAttr)) { 
                parserContext.getReaderContext().error("The 'location' attribute is required.", parserContext.extractSource(element));
                return null;
            } else { 
                ManagedList<String> locations = new ManagedList();
                locations.addAll(Arrays.asList(StringUtils.commaDelimitedListToStringArray(locationAttr)));
                RootBeanDefinition resourceHandlerDef = new RootBeanDefinition(ResourceHttpRequestHandler.class);
                resourceHandlerDef.setSource(source);
                resourceHandlerDef.setRole(2);
                resourceHandlerDef.getPropertyValues().add("locations", locations);
                // 这里对cache-period 解析
                String cacheSeconds = element.getAttribute("cache-period");
                if (StringUtils.hasText(cacheSeconds)) { 
                    resourceHandlerDef.getPropertyValues().add("cacheSeconds", cacheSeconds);
                }
    
                Element cacheControlElement = DomUtils.getChildElementByTagName(element, "cache-control");
                if (cacheControlElement != null) { 
                    CacheControl cacheControl = this.parseCacheControl(cacheControlElement);
                    resourceHandlerDef.getPropertyValues().add("cacheControl", cacheControl);
                }
    
                Element resourceChainElement = DomUtils.getChildElementByTagName(element, "resource-chain");
                if (resourceChainElement != null) { 
                    this.parseResourceChain(resourceHandlerDef, parserContext, resourceChainElement, source);
                }
    
                String beanName = parserContext.getReaderContext().generateBeanName(resourceHandlerDef);
                parserContext.getRegistry().registerBeanDefinition(beanName, resourceHandlerDef);
                parserContext.registerComponent(new BeanComponentDefinition(resourceHandlerDef, beanName));
                return beanName;
            }
        }

ResourceHttpRequestHandler 类注释如下

{ @link HttpRequestHandler} that serves static resources optimized for superior browser performance
     * (according to the guidelines of Page Speed, YSlow, etc.) by allowing for flexible cache settings
     * ({ @linkplain #setCacheSeconds "cacheSeconds" property}, last-modified support).

大概意思就是对静态化资源缓存做了一个灵活的属性配置、

[2]: /images/20220327/43e326b7e9a1495a8db8a5cd40cf7122.png