<!--   該過濾器使得開發者可以通過org.jasig.cas.client.util.AssertionHolder來獲取使用者的登入名。   
         比如AssertionHolder.getAssertion().getPrincipal().getName()
   -->  
<filter>   
    <filter-name>CAS Assertion Thread Local Filter</filter-name>    
    <filter-class>org.jasig.cas.client.util.AssertionThreadLocalFilter</filter-class> 
</filter> 

<filter-mapping>   
    <filter-name>CAS Assertion Thread Local Filter</filter-name>   
    <url-pattern>/*</url-pattern> 
</filter-mapping>   
 

    public void doFilter(final ServletRequest servletRequest, final ServletResponse servletResponse, final FilterChain filterChain) throws IOException, ServletException {  
            //轉換引數  
            final HttpServletRequest request = (HttpServletRequest) servletRequest;  
            final HttpSession session = request.getSession(false);  
            //取得Assertion物件，如果session為null則從request中取得，否則從session中取得。  
            final Assertion assertion = (Assertion) (session == null ? request.getAttribute(AbstractCasFilter.CONST_CAS_ASSERTION) : session.getAttribute(AbstractCasFilter.CONST_CAS_ASSERTION));  
      
            try {  
                //繫結到ThreadLocal  
                AssertionHolder.setAssertion(assertion);  
                // 處理後面的過濾器，這樣後面的Fileter和Servlet可以線上程中取得Assertion物件。  
                filterChain.doFilter(servletRequest, servletResponse);  
            } finally {  
                //處理完畢後清理執行緒  
                AssertionHolder.clear();  
            }  
        }  
 

public class AssertionHolder {

    /**
     * ThreadLocal to hold the Assertion for Threads to access.
     */
    private static final ThreadLocal<Assertion> threadLocal = new ThreadLocal<Assertion>();


    /**
     * Retrieve the assertion from the ThreadLocal.
     *
     * @return the Asssertion associated with this thread.
     */
    public static Assertion getAssertion() {
        return threadLocal.get();
    }

    /**
     * Add the Assertion to the ThreadLocal.
     *
     * @param assertion the assertion to add.
     */
    public static void setAssertion(final Assertion assertion) {
        threadLocal.set(assertion);
    }

    /**
     * Clear the ThreadLocal.
     */
    public static void clear() {
        threadLocal.set(null);
    }
}