DelegatingFilterProxy分析

vboy1010 發(fā)布于2019-08-15 15:18 / 2063人閱讀

前言

最近在分析源碼時發(fā)現(xiàn)了一個配置如下：

#web.xml文件中

    cacheSessionFilter
    org.springframework.web.filter.DelegatingFilterProxy
    
        targetFilterLifecycle
        true
    


    
    /*


#applicationContext.xml文件

那么這個DelegatingFilterProxy到底是干嘛用的那？？？網(wǎng)上查了很多，最終總結(jié)為一句話即：DelegateFilterProxy實(shí)現(xiàn)了服務(wù)器容器（tomcate was等）中的filter調(diào)用spring容器中類的功能，那這是如何實(shí)現(xiàn)的那？

DelegatingFilterProxy和spring容器如何關(guān)聯(lián)的？

觀察web.xml文件，spring的初始化一般都是在非常靠前的，也就是說在使用delegatingfilterproxy之前，spring容器已經(jīng)初始化完成了，然后觀察delegatingfilterproxy的源碼會發(fā)現(xiàn)有這么一段

protected void initFilterBean() throws ServletException {
        synchronized (this.delegateMonitor) {
            if (this.delegate == null) {
                // If no target bean name specified, use filter name.
                if (this.targetBeanName == null) {
                    this.targetBeanName = getFilterName();
                }
                // Fetch Spring root application context and initialize the delegate early,
                // if possible. If the root application context will be started after this
                // filter proxy, we"ll have to resort to lazy initialization.
                WebApplicationContext wac = findWebApplicationContext();
                if (wac != null) {
                    this.delegate = initDelegate(wac);
                }
            }
        }
    }

沒錯WebApplicationContext其實(shí)就是spring容器，也就是說DelegatingFilterProxy中保存有spring的容器，而在WebApplicationContext中有一個和DelegatingFilerProxy同名的類（這個類就是我們自己的類），DelegatingFilterProxy會從WebApplicationContext中尋找那個和其同名的類，然后將所有的動作賦予給它。

public void doFilter(ServletRequest request, ServletResponse response, FilterChain filterChain)
            throws ServletException, IOException {

        // Lazily initialize the delegate if necessary.
        Filter delegateToUse = this.delegate;
        if (delegateToUse == null) {
            synchronized (this.delegateMonitor) {
                delegateToUse = this.delegate;
                if (delegateToUse == null) {
                    WebApplicationContext wac = findWebApplicationContext();
                    if (wac == null) {
                        throw new IllegalStateException("No WebApplicationContext found: " +
                                "no ContextLoaderListener or DispatcherServlet registered?");
                    }
                    delegateToUse = initDelegate(wac);
                }
                this.delegate = delegateToUse;
            }
        }

        // Let the delegate perform the actual doFilter operation.
        invokeDelegate(delegateToUse, request, response, filterChain);
    }

其中的delegateToUse就是從webapplicationcontext中取出來的：

@Override
    protected void initFilterBean() throws ServletException {
        synchronized (this.delegateMonitor) {
            if (this.delegate == null) {
                // If no target bean name specified, use filter name.
                if (this.targetBeanName == null) {
                    this.targetBeanName = getFilterName();
                }
                // Fetch Spring root application context and initialize the delegate early,
                // if possible. If the root application context will be started after this
                // filter proxy, we"ll have to resort to lazy initialization.
                WebApplicationContext wac = findWebApplicationContext();
                if (wac != null) {
                    this.delegate = initDelegate(wac);
                }
            }
        }
    }