cas-client-core单点登录排除不需要拦截的URL

　　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。

    protected void initInternal(final FilterConfig filterConfig) throws ServletException {
        if (!isIgnoreInitConfiguration()) {
            super.initInternal(filterConfig);
            setCasServerLoginUrl(getString(ConfigurationKeys.CAS_SERVER_LOGIN_URL));
            setRenew(getBoolean(ConfigurationKeys.RENEW));
            setGateway(getBoolean(ConfigurationKeys.GATEWAY));
                       
            final String ignorePattern = getString(ConfigurationKeys.IGNORE_PATTERN);
            final String ignoreUrlPatternType = getString(ConfigurationKeys.IGNORE_URL_PATTERN_TYPE);
            
            if (ignorePattern != null) {
                final Class<? extends UrlPatternMatcherStrategy> ignoreUrlMatcherClass = PATTERN_MATCHER_TYPES.get(ignoreUrlPatternType);
                if (ignoreUrlMatcherClass != null) {
                    this.ignoreUrlPatternMatcherStrategyClass = ReflectUtils.newInstance(ignoreUrlMatcherClass.getName());
                } else {
                    try {
                        logger.trace("Assuming {} is a qualified class name...", ignoreUrlPatternType);
                        this.ignoreUrlPatternMatcherStrategyClass = ReflectUtils.newInstance(ignoreUrlPatternType);
                    } catch (final IllegalArgumentException e) {
                        logger.error("Could not instantiate class [{}]", ignoreUrlPatternType, e);
                    }
                }

　　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<String> IGNORE_PATTERN = new ConfigurationKey<String>("ignorePattern", null);
    ConfigurationKey<String> IGNORE_URL_PATTERN_TYPE = new ConfigurationKey<String>("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。

    private static final Map<String, Class<? extends UrlPatternMatcherStrategy>> PATTERN_MATCHER_TYPES =
            new HashMap<String, Class<? extends UrlPatternMatcherStrategy>>();
    
    static {
        PATTERN_MATCHER_TYPES.put("CONTAINS", ContainsPatternUrlPatternMatcherStrategy.class);
        PATTERN_MATCHER_TYPES.put("REGEX", RegexUrlPatternMatcherStrategy.class);
        PATTERN_MATCHER_TYPES.put("EXACT", ExactUrlPatternMatcherStrategy.class);
    }

　　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）。

 <filter>
      <filter-name>casAuthenticationFilter</filter-name>
   <filter-class>org.jasig.cas.client.authentication.AuthenticationFilter</filter-class>
      <init-param>
         <param-name>casServerLoginUrl</param-name>
         <param-value>http://cas.eguid.cc/cas-server/</param-value>
      </init-param>
      <init-param>
         <param-name>serverName</param-name>
         <param-value>http://cilent.eguid.cc/</param-value>
      </init-param>
      <init-param>
         <description>不拦截的请求</description>
         <param-name>ignorePattern</param-name>
         <param-value>/service/</param-value>
      </init-param>
      <init-param>
         <description>识别模式</description>
         <param-name>ignoreUrlPatternType</param-name>
         <param-value>CONTAINS</param-value>
      </init-param>
   </filter>
   <filter-mapping>
      <filter-name>casAuthenticationFilter</filter-name>
      <url-pattern>/*</url-pattern>