同事提了一个要求，要求对外提供的接口不需要经过单点登录验证，我刚开始想，这简单，提供不需要拦截的url数组，在AuthenticationFilter里面对url进行检查，在此数组内，就不需要拦截。

　　下面是AuthenticationFilter类的doFilter方法的部分源码：

public final void doFilter(final ServletRequest servletRequest, final ServletResponse servletResponse,            final FilterChain filterChain) throws IOException, ServletException {                final HttpServletRequest request = (HttpServletRequest) servletRequest;        final HttpServletResponse response = (HttpServletResponse) servletResponse; 　　　　　//在此写验证url        if (isRequestUrlExcluded(request)) {            logger.debug("Request is ignored.");            filterChain.doFilter(request, response);            return;        }        final HttpSession session = request.getSession(false);        final Assertion assertion = session != null ? (Assertion) session.getAttribute(CONST_CAS_ASSERTION) : null;        if (assertion != null) {            filterChain.doFilter(request, response);            return;        }

　　以上是部分源码，本来我想在注释的地方，对url进行检查，但是下面一行的 isRequestUrlExcluded(request)，这不正是检查URL排除的地方吗？原来cas-client已经实现了此功能。下面我们一步步的梳理代码。

　　isRequestUrlExcluded的方法如下：

private boolean isRequestUrlExcluded(final HttpServletRequest request) {        if (this.ignoreUrlPatternMatcherStrategyClass == null) {            return false;        }                final StringBuffer urlBuffer = request.getRequestURL();        if (request.getQueryString() != null) {            urlBuffer.append("?").append(request.getQueryString());        }        final String requestUri = urlBuffer.toString();        return this.ignoreUrlPatternMatcherStrategyClass.matches(requestUri);    }

　　我们可以看到这里的关键是ignoreUrlPatternMatcherStrategyClass，忽略Url模式验证策略类。

1     protected void initInternal(final FilterConfig filterConfig) throws ServletException { 2         if (!isIgnoreInitConfiguration()) { 3             super.initInternal(filterConfig); 4             setCasServerLoginUrl(getString(ConfigurationKeys.CAS_SERVER_LOGIN_URL)); 5             setRenew(getBoolean(ConfigurationKeys.RENEW)); 6             setGateway(getBoolean(ConfigurationKeys.GATEWAY)); 7                         8             final String ignorePattern = getString(ConfigurationKeys.IGNORE_PATTERN); 9             final String ignoreUrlPatternType = getString(ConfigurationKeys.IGNORE_URL_PATTERN_TYPE);10             11             if (ignorePattern != null) {12                 final Class
      ignoreUrlMatcherClass = PATTERN_MATCHER_TYPES.get(ignoreUrlPatternType);13                 if (ignoreUrlMatcherClass != null) {14                     this.ignoreUrlPatternMatcherStrategyClass = ReflectUtils.newInstance(ignoreUrlMatcherClass.getName());15                 } else {16                     try {17                         logger.trace("Assuming {} is a qualified class name...", ignoreUrlPatternType);18                         this.ignoreUrlPatternMatcherStrategyClass = ReflectUtils.newInstance(ignoreUrlPatternType);19                     } catch (final IllegalArgumentException e) {20                         logger.error("Could not instantiate class [{}]", ignoreUrlPatternType, e);21                     }22                 }

　　红色部分是实例化，是关键。我们从第八行开始看起，分别是获取ignorePattern和ignoreUrlPatternType参数，两者的意思分别是忽略的url和忽略的模式。

ConfigurationKey
     
       IGNORE_PATTERN = new ConfigurationKey
      
       ("ignorePattern", null);    ConfigurationKey
       
         IGNORE_URL_PATTERN_TYPE = new ConfigurationKey
        
         ("ignoreUrlPatternType", "REGEX");
        
       
      
     

　　可以看到代码默认的识别url的方式是正则表达式。而识别方式一共有三种，我们看一下PATTERN_MATCHER_TYPES，分别是包含、正则和精确。

1     private static final Map
     
      > PATTERN_MATCHER_TYPES =2             new HashMap
      
       >();3     4     static {5         PATTERN_MATCHER_TYPES.put("CONTAINS", ContainsPatternUrlPatternMatcherStrategy.class);6         PATTERN_MATCHER_TYPES.put("REGEX", RegexUrlPatternMatcherStrategy.class);7         PATTERN_MATCHER_TYPES.put("EXACT", ExactUrlPatternMatcherStrategy.class);8     }
      
     

　　因此，我们只需在web.xml中的过滤器上添加参数来配置不需要单点登录拦截url（例子是如果url中包含/service/，则不需要经过单点登录验证）。

           
      
       casAuthenticationFilter
         
      
       org.jasig.cas.client.authentication.AuthenticationFilter
            
               
       
        casServerLoginUrl
                
       
        http://cas.eguid.cc/cas-server/
             
            
               
       
        serverName
                
       
        http://cilent.eguid.cc/
             
            
               
       
        不拦截的请求
                
       
        ignorePattern
                
       
        /service/
             
            
               
       
        识别模式
                
       
        ignoreUrlPatternType
                
       
        CONTAINS
             
         
        
           
      
       casAuthenticationFilter
            
      
       /*