SpringSecurity过滤器链加载原理

项目dubug启动，加载web.xml文件,

<filter>
        <filter-name>springSecurityFilterChain</filter-name>
        <filter-class>org.springframework.web.filter.DelegatingFilterProxy</filter-class>
    </filter>
    <filter-mapping>
        <filter-name>springSecurityFilterChain</filter-name>
        <url-pattern>/*
    

 public final void init(FilterConfig filterConfig) throws ServletException {
        Assert.notNull(filterConfig, "FilterConfig must not be null");
        if (this.logger.isDebugEnabled()) {
            this.logger.debug("Initializing filter '" + filterConfig.getFilterName() + "'");
        }

        this.filterConfig = filterConfig;
        PropertyValues pvs = new GenericFilterBean.FilterConfigPropertyValues(filterConfig, this.requiredProperties);
        if (!pvs.isEmpty()) {
            try {
                BeanWrapper bw = PropertyAccessorFactory.forBeanPropertyAccess(this);
                ResourceLoader resourceLoader = new ServletContextResourceLoader(filterConfig.getServletContext());
                Environment env = this.environment;
                if (env == null) {
                    env = new StandardServletEnvironment();
                }

                bw.registerCustomEditor(Resource.class, new ResourceEditor(resourceLoader, (PropertyResolver)env));
                this.initBeanWrapper(bw);
                bw.setPropertyValues(pvs, true);
            } catch (BeansException var6) {
                String msg = "Failed to set bean properties on filter '" + filterConfig.getFilterName() + "': " + var6.getMessage();
                this.logger.error(msg, var6);
                throw new NestedServletException(msg, var6);
            }
        }

        this.initFilterBean();
        if (this.logger.isDebugEnabled()) {
            this.logger.debug("Filter '" + filterConfig.getFilterName() + "' configured successfully");
        }

    }

执行init方法，调用其子类 this.initFilterBean();

 protected void initFilterBean() throws ServletException {
        Object var1 = this.delegateMonitor;
        synchronized(this.delegateMonitor) {
            if (this.delegate == null) {
                if (this.targetBeanName == null) {
                    this.targetBeanName = this.getFilterName();
                }

                WebApplicationContext wac = this.findWebApplicationContext();
                if (wac != null) {
                    this.delegate = this.initDelegate(wac);
                }
            }

        }
    }

接着，调用其本身的this.initDelegate(wac);方法，Filter delegate = (Filter)wac.getBean(targetBeanName, Filter.class);在当前作用域获取对象名字为springSecurityFilterChain的，返回一个过滤器对象

protected Filter initDelegate(WebApplicationContext wac) throws ServletException {
        String targetBeanName = this.getTargetBeanName();
        Assert.state(targetBeanName != null, "No target bean name set");
        Filter delegate = (Filter)wac.getBean(targetBeanName, Filter.class);
        if (this.isTargetFilterLifecycle()) {
            delegate.init(this.getFilterConfig());
        }

        return delegate;
    }

当访问本项目时，执行了上面返回的过滤器对象的doFilter()方法，

public void doFilter(ServletRequest request, ServletResponse response,
			FilterChain chain) throws IOException, ServletException {
		boolean clearContext = request.getAttribute(FILTER_APPLIED) == null;
		if (clearContext) {
			try {
				request.setAttribute(FILTER_APPLIED, Boolean.TRUE);
				doFilterInternal(request, response, chain);
			}
			finally {
				SecurityContextHolder.clearContext();
				request.removeAttribute(FILTER_APPLIED);
			}
		}
		else {
			doFilterInternal(request, response, chain);
		}
	}

不管是否，都执行其doFilterInternal()方法，

private void doFilterInternal(ServletRequest request, ServletResponse response,
			FilterChain chain) throws IOException, ServletException {

		FirewalledRequest fwRequest = firewall
				.getFirewalledRequest((HttpServletRequest) request);
		HttpServletResponse fwResponse = firewall
				.getFirewalledResponse((HttpServletResponse) response);

		List<Filter> filters = getFilters(fwRequest);

		if (filters == null || filters.size() == 0) {
			if (logger.isDebugEnabled()) {
				logger.debug(UrlUtils.buildRequestUrl(fwRequest)
						+ (filters == null ? " has no matching filters"
								: " has an empty filter list"));
			}

			fwRequest.reset();

			chain.doFilter(fwRequest, fwResponse);

			return;
		}

		VirtualFilterChain vfc = new VirtualFilterChain(fwRequest, chain, filters);
		vfc.doFilter(fwRequest, fwResponse);
	}
	private List<Filter> getFilters(HttpServletRequest request) {
		for (SecurityFilterChain chain : filterChains) {
			if (chain.matches(request)) {
				return chain.getFilters();
			}
		}

		return null;
	}

List filters = getFilters(fwRequest);这一行就是返回的过滤器链，

for (SecurityFilterChain chain : filterChains) {
			if (chain.matches(request)) {
				return chain.getFilters();
			}
		}

由此可见，过滤器链中的每个过滤器对象是SecurityFilterChain