springSecurity源码分析——DelegatingFilterProxy类的作用

来源：http://www.cnblogs.com/hzhuxin/archive/2011/12/19/2293730.html

 

使用过springSecurity的朋友都知道，首先需要在web.xml进行以下配置，

<filter>
  <filter-name>springSecurityFilterChain</filter-name>
  <filter-class>org.springframework.web.filter.DelegatingFilterProxy</filter-class> 

  <init-param>

        <param-name>targetFilterLifecycle</param-name>
        <param-value>true</param-value>  <!-- 默认是false -->
    </init-param>

 </filter>

<filter-mapping>
  <filter-name>springSecurityFilterChain</filter-name>
  <url-pattern>/*</url-pattern>

 </filter-mapping>

 

从这个配置中，可能会给我们造成一个错觉，以为DelegatingFilterProxy类就是springSecurity的入口，但其实这个类位于spring-web-3.0.5.RELEASE.jar这个jar下面，说明这个类本身是和springSecurity无关。DelegatingFilterProxy类继承于抽象类GenericFilterBean,间接地implement 了javax.servlet.Filter接口，Servlet容器在启动时，首先会调用Filter的init方法,GenericFilterBean的作用主要是可以把Filter的初始化参数自动地set到继承于GenericFilterBean类的Filter中去。在其init方法的如下代码就是做了这个事：

PropertyValues pvs = new FilterConfigPropertyValues(filterConfig, this.requiredProperties); 
BeanWrapper bw = PropertyAccessorFactory.forBeanPropertyAccess(this); 
ResourceLoader resourceLoader = new ServletContextResourceLoader(filterConfig.getServletContext()); 
bw.registerCustomEditor(Resource.class, new ResourceEditor(resourceLoader)); 
initBeanWrapper(bw); 
bw.setPropertyValues(pvs, true); 

 

 

 另外在init方法中调用了initFilterBean()方法，该方法是GenericFilterBean类是特地留给子类扩展用的，

protected void initFilterBean() throws ServletException { 
        // 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. 
        synchronized (this.delegateMonitor) { 
            WebApplicationContext wac = findWebApplicationContext(); 
            if (wac != null) { 
                this.delegate = initDelegate(wac); 
            } 
        } 
    } 

 

 可以看出上述代码首先看Filter是否提供了targetBeanName初始化参数，如果没有提供则直接使用filter的name做为beanName,产生了beanName后，由于我们在web.xml的filter的name是springSecurityFilterChain,从spring的IOC容器中取出bean的代码是initDelegate方法，下面是该方法代码：

protected Filter initDelegate(WebApplicationContext wac) throws ServletException { 
        Filter delegate = wac.getBean(getTargetBeanName(), Filter.class); 
        if (isTargetFilterLifecycle()) { 
            delegate.init(getFilterConfig()); 
        } 
        return delegate;

 

 

 通过跟踪代码，发现取出的bean是org.springframework.security.FilterChainProxy，该类也是继承于GenericFilterBean,取出bean后，判断targetFilterLifecycle属性是false还是true,决定是否调用该类的init方法。这个FilterChainProxy bean实例最终被保存在DelegatingFilterProxy类的delegate属性里,

下面看一下DelegatingFilterProxy类的doFilter方法

public void doFilter(ServletRequest request, ServletResponse response, FilterChain filterChain) 
            throws ServletException, IOException { 
  
        // Lazily initialize the delegate if necessary. 
        Filter delegateToUse = null; 
        synchronized (this.delegateMonitor) { 
            if (this.delegate == null) { 
                WebApplicationContext wac = findWebApplicationContext(); 
                if (wac == null) { 
                    throw new IllegalStateException("No WebApplicationContext found: no ContextLoaderListener registered?"); 
                } 
                this.delegate = initDelegate(wac); 
            } 
            delegateToUse = this.delegate; 
        } 
  
        // Let the delegate perform the actual doFilter operation. 
        invokeDelegate(delegateToUse, request, response, filterChain); 
    }

 

 

 

 真正要关注invokeDelegate(delegateToUse, request, response, filterChain);这句代码,在下面可以看出DelegatingFilterProxy类实际是用其delegate属性即org.springframework.security.FilterChainProxy实例的doFilter方法来响应请求。

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

 

以上就是DelegatingFilterProxy类的一些内部运行机制，其实主要作用就是一个代理模式的应用,可以把servlet 容器中的filter同spring容器中的bean关联起来。

此外还要注意一个DelegatingFilterProxy的一个初始化参数：targetFilterLifecycle ,其默认值为false 。 但如果被其代理的filter的init()方法和destry()方法需要被调用时，需要设置targetFilterLifecycle为true。具体可见DelegatingFilterProxy中的如下代码：

 

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); 
                } 
            } 
        } 
    } 
  
  
protected Filter initDelegate(WebApplicationContext wac) throws ServletException { 
        Filter delegate = wac.getBean(getTargetBeanName(), Filter.class); 
        if (isTargetFilterLifecycle()) {    //注意这行 
            delegate.init(getFilterConfig()); 
        } 
        return delegate; 
    }

 

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