spring mvc 源码简要分析

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关于web项目，运用比较多的是过滤器和拦截器

过滤器基于责任链设计模式

创建过滤器链

/ Create the filter chain for this request
ApplicationFilterChain filterChain =
        ApplicationFilterFactory.createFilterChain(request, wrapper, servlet);

//调用

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

    // Call the next filter if there is one
    if (pos < n) {
        ApplicationFilterConfig filterConfig = filters[pos++];
        try {
            Filter filter = filterConfig.getFilter();

            if (request.isAsyncSupported() && "false".equalsIgnoreCase(
                    filterConfig.getFilterDef().getAsyncSupported())) {
                request.setAttribute(Globals.ASYNC_SUPPORTED_ATTR, Boolean.FALSE);
            }
            if( Globals.IS_SECURITY_ENABLED ) {
                final ServletRequest req = request;
                final ServletResponse res = response;
                Principal principal =
                    ((HttpServletRequest) req).getUserPrincipal();

                Object[] args = new Object[]{req, res, this};
                SecurityUtil.doAsPrivilege ("doFilter", filter, classType, args, principal);
            } else {
                filter.doFilter(request, response, this);
            }
        } catch (IOException | ServletException | RuntimeException e) {
            throw e;
        } catch (Throwable e) {
            e = ExceptionUtils.unwrapInvocationTargetException(e);
            ExceptionUtils.handleThrowable(e);
            throw new ServletException(sm.getString("filterChain.filter"), e);
        }
        return;
    }

    // We fell off the end of the chain -- call the servlet instance
    try {
        if (ApplicationDispatcher.WRAP_SAME_OBJECT) {
            lastServicedRequest.set(request);
            lastServicedResponse.set(response);
        }

        if (request.isAsyncSupported() && !servletSupportsAsync) {
            request.setAttribute(Globals.ASYNC_SUPPORTED_ATTR,
                    Boolean.FALSE);
        }
        // Use potentially wrapped request from this point
        if ((request instanceof HttpServletRequest) &&
                (response instanceof HttpServletResponse) &&
                Globals.IS_SECURITY_ENABLED ) {
            final ServletRequest req = request;
            final ServletResponse res = response;
            Principal principal =
                ((HttpServletRequest) req).getUserPrincipal();
            Object[] args = new Object[]{req, res};
            SecurityUtil.doAsPrivilege("service",
                                       servlet,
                                       classTypeUsedInService,
                                       args,
                                       principal);
        } else {
            servlet.service(request, response);
        }
    } catch (IOException | ServletException | RuntimeException e) {
        throw e;
    } catch (Throwable e) {
        e = ExceptionUtils.unwrapInvocationTargetException(e);
        ExceptionUtils.handleThrowable(e);
        throw new ServletException(sm.getString("filterChain.servlet"), e);
    } finally {
        if (ApplicationDispatcher.WRAP_SAME_OBJECT) {
            lastServicedRequest.set(null);
            lastServicedResponse.set(null);
        }
    }