Filter责任链模式

 

 

Filter责任链的创建

org.apache.catalina.core.ApplicationFilterFactory#createFilterChain,  此方法是被org.apache.catalina.core.StandardWrapperValve#invoke调用的,  对每个request都会创建FilterChain

public static ApplicationFilterChain createFilterChain(ServletRequest request,Wrapper wrapper, Servlet servlet) {
//传入参数必须有一个servlet，这个servlet是在链的末尾被调用的. 这个servlet的查找过程是根据request的URI从web.xml配置中匹配出来的// If there is no servlet to execute, return nullif (servlet == null)return null;// Create and initialize a filter chain objectApplicationFilterChain filterChain = null;if (request instanceof Request) {//.....} else {// Request dispatcher in usefilterChain = new ApplicationFilterChain();}
// 责任链上绑定一个servletfilterChain.setServlet(servlet);filterChain.setServletSupportsAsync(wrapper.isAsyncSupported());// Acquire the filter mappings for this ContextStandardContext context = (StandardContext) wrapper.getParent();FilterMap filterMaps[] = context.findFilterMaps();// If there are no filter mappings, we are doneif ((filterMaps == null) || (filterMaps.length == 0))return (filterChain);// ...
//根据web.xml中filter的配置查找是否和当前request匹配// Add the relevant path-mapped filters to this filter chainfor (int i = 0; i < filterMaps.length; i++) {if (!matchDispatcher(filterMaps[i] ,dispatcher)) {continue;}if (!matchFiltersURL(filterMaps[i], requestPath))continue;ApplicationFilterConfig filterConfig = (ApplicationFilterConfig)context.findFilterConfig(filterMaps[i].getFilterName());if (filterConfig == null) {// FIXME - log configuration problemcontinue;}
// 和request URI匹配，则filter会加入到责任链中filterChain.addFilter(filterConfig);}/.....// Return the completed filter chainreturn filterChain;}

 

filterChain创建完成后就会调用doFilter启用这个链,  此方法也是被org.apache.catalina.core.StandardWrapperValve#invoke调用的

org.apache.catalina.core.ApplicationFilterChain#doFilter 

private void internalDoFilter(ServletRequest request,
                                  ServletResponse response)
        throws IOException, ServletException {

        // Call the next filter if there is one  
        if (pos < n) {
            //调用下一个filter, 每调用一次 当前pos都会++
            ApplicationFilterConfig filterConfig = filters[pos++];
            try {
                Filter filter = filterConfig.getFilter();

                //...
                    filter.doFilter(request, response, this);
                
            } catch (IOException | ServletException | RuntimeException e) {
                throw e;
            } catch (Throwable e) {
               // ...
            }
            return;
        }

        // We fell off the end of the chain -- call the servlet instance
        try {
            if (request.isAsyncSupported() && !servletSupportsAsync) {
                request.setAttribute(Globals.ASYNC_SUPPORTED_ATTR,
                        Boolean.FALSE);
            }
            // ...  在链的末尾，调用具体servlet的doService
                servlet.service(request, response);
            //
        } catch (IOException | ServletException | RuntimeException e) {
            throw e;
        } catch (Throwable e) {
           //...
        } finally {
           //...
        }
    }