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>