代理過濾器

DelegatingFilterProxy這個東西太熟悉了，在相似shiro和springsecurity的權限認證框架都有見到它的身影，但又陌生，印象彷佛只停留在DelegatingFilterProxy把servlet 容器中的filter同spring容器中的bean關聯起來，交由spring容器管理。DelegatingFilterProxy代理類把filter和IOC容器進行告終合在一塊兒，從spring上下文尋找要代理的過濾類，執行初始化，過濾和銷燬過程。下面結合springsecurity就翻翻源碼：

獲取filter配置參數

DelegatingFilterProxy繼承了GenericFilterBean ，父類實現了一堆接口：

public abstract class GenericFilterBean implements Filter, BeanNameAware, EnvironmentAware, EnvironmentCapable, ServletContextAware, InitializingBean, DisposableBean 複製代碼

• BeanNameAware //返回當前的beanName
• EnvironmentAware//讀取配置文件
• EnvironmentCapable//檢查接受了BeanFactory接口的框架方法
• ServletContextAware//獲取ServletContext
• InitializingBean//初始化bean對象
• DisposableBean //銷燬bean

父類中init方法將過濾器的參數配置傳遞給代理對象 源碼以下：

public final void init(FilterConfig filterConfig) throws ServletException {
        Assert.notNull(filterConfig, "FilterConfig must not be null");
        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);
            }
        }
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bean對象初始化

獲取目標對象的name。

protected void initFilterBean() throws ServletException {
        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);
                }
            }

        }
    }
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初始化代理對象

在web.xml文件中配置的org.springframework.web.context.ContextLoaderListener實現加載Sping的上下文環境 （由XmlWebApplicationContent來裝載）。 經過initDelegate(wac)獲得代理過濾器

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;
    }
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代理執行過濾方法

在執行過濾方法以前，經過invokeDelegate調用delegate執行過濾方法

protected void invokeDelegate(Filter delegate, ServletRequest request, ServletResponse response, FilterChain filterChain) throws ServletException, IOException {
        delegate.doFilter(request, response, filterChain);
    }
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過濾方法

public void doFilter(ServletRequest request, ServletResponse response, FilterChain filterChain) throws ServletException, IOException {
        Filter delegateToUse = this.delegate;
        if (delegateToUse == null) {
            synchronized(this.delegateMonitor) {
                delegateToUse = this.delegate;
                if (delegateToUse == null) {
                    WebApplicationContext wac = this.findWebApplicationContext();
                    if (wac == null) {
                        throw new IllegalStateException("No WebApplicationContext found: no ContextLoaderListener or DispatcherServlet registered?");
                    }

                    delegateToUse = this.initDelegate(wac);
                }

                this.delegate = delegateToUse;
            }
        }
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銷燬

protected void destroyDelegate(Filter delegate) {
        if (this.isTargetFilterLifecycle()) {
            delegate.destroy();
        }

    }
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shiro的代理過濾器大體相似。