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<? extends UrlPatternMatcherStrategy> 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<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。
1 private static final Map<String, Class<? extends UrlPatternMatcherStrategy>> PATTERN_MATCHER_TYPES =
2 new HashMap<String, Class<? extends UrlPatternMatcherStrategy>>(); 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）。
<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>