SpringSecurity3源码分析
web.xml中的过滤器：DelegatingFilterProxy
<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>/*</url-pattern>
</filter-mapping>
DelegatingFilterProxy类位于spring-web-3.0.5.RELEASE.jar下面，说明这个类本身是和springSecurity无关。DelegatingFilterProxy类继承于抽象类GenericFilterBean，间接地实现了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件事：
public final void init(FilterConfig filterConfig) throws ServletException {
Assert.notNull(filterConfig,”FilterConfig must not be null”);
if (logger.isDebugEnabled()) {
logger.debug(“Initializingfilter ‘” + filterConfig.getFilterName() + “‘”);
}
this.filterConfig = filterConfig;
// Set bean properties frominit parameters.
try {
PropertyValues pvs = newFilterConfigPropertyValues(filterConfig, this.requiredProperties);
BeanWrapperbw = PropertyAccessorFactory.forBeanPropertyAccess(this);
ResourceLoaderresourceLoader = newServletContextResourceLoader(filterConfig.getServletContext());
bw.registerCustomEditor(Resource.class, new ResourceEditor(resourceLoader, this.environment));
initBeanWrapper(bw);
bw.setPropertyValues(pvs,true);
}
catch (BeansException ex) {
String msg = “Failedto set bean properties on filter ‘” +
filterConfig.getFilterName()+ “‘: ” + ex.getMessage();
logger.error(msg,ex);
throw new NestedServletException(msg, ex);
}
// Let subclasses do whateverinitialization they like.
initFilterBean();
if (logger.isDebugEnabled()) {
logger.debug(“Filter'” + filterConfig.getFilterName() + “‘ configured successfully”);
}
}
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：
@Override
protected voidinitFilterBean() throws ServletException {
synchronized (this.delegateMonitor){
if (this.delegate== null) {
// If notarget bean name specified, use filter name.
if (this.targetBeanName== null) {
this.targetBeanName= getFilterName();
}
// FetchSpring root application context and initialize the delegate early,
// ifpossible. If the root application context will be started after this
// filterproxy, we’ll have to resort to lazy initialization.
WebApplicationContextwac = 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 FilterinitDelegate(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FilterChainProxybean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 voiddoFilter(ServletRequest request, ServletResponse response, FilterChainfilterChain)
throwsServletException, IOException {
//Lazily initialize the delegate if necessary.
FilterdelegateToUse = this.delegate;
if(delegateToUse == null) {
synchronized(this.delegateMonitor) {
if(this.delegate == null) {
WebApplicationContextwac = findWebApplicationContext();
if(wac == null) {
thrownew IllegalStateException(“No WebApplicationContext found: noContextLoaderListener 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 voidinvokeDelegate(
Filterdelegate, ServletRequest request, ServletResponse response, FilterChainfilterChain)
throwsServletException, 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。
