spring认证的一些核心类

SecurityContextHolder, to provide access to the SecurityContext. 
SecurityContext: to hold the Authentication and possibly request-specific security information. 
Authentication: 表示用户认证信息
GrantedAuthority: 当前用户拥有的权限，通过Authentication的getAuthorities()获取，是一个数组。 
UserDetails: 定义了一些可以获取用户名、密码、权限等与认证相关的信息的方法,通过UserDetailsService的loadUserByUsername()方法进行加载。
UserDetailsService: org.springframework.security.core.userdetails.jdbc.JdbcDaoImpl(通过数据库或内存获取UserDetails)
UserDetailsService->UserDetails
UserDetailsService->GrantedAuthority(role)
SecurityContextHolder->SecurityContext->Authentication(principal,)
加载用户dao相关：
UserDetailsService(接口):loadUserByUsername(String username) 子类
    UserDetailsManager:(接口)changePassword(String oldPassword, String newPassword),createUser(UserDetails user),deleteUser(String username)等
    CachingUserDetailsService:
    InMemoryUserDetailsManager: 
    JdbcDaoImpl:
        JdbcUserDetailsManager: 
    LdapUserDetailsManager:
    LdapUserDetailsService:
用户信息相关：
UserDetails：(接口)getAuthorities(),getPassword(),getUsername(),isAccountNonExpired()等
    InetOrgPerson：
    LdapUserDetailsImpl:
    LdapUserDetailsImpl:
    Person:UserDetails implementation whose properties are based on the LDAP schema for Person.
    User:(类)
认证相关：
Principal：(java.security)equals(Object another),getName() 
    Authentication：(接口)一旦一个request被认证，Authentication 就会被放入 thread-local SecurityContext managed by the SecurityContextHolder 
                    SecurityContextHolder.getContext().setAuthentication(anAuthentication);显式认证，
                    Collection<? extends GrantedAuthority> getAuthorities(),getCredentials(), getDetails(),getPrincipal()
        UsernamePasswordAuthenticationToken：for simple presentation of a username and password. 
        RememberMeAuthenticationToken:
        OpenIDAuthenticationToken:
        ...
GrantedAuthority:(接口)getAuthority()该方法返回一个字符串，表示对应权限的字符串表示，如果对应权限不能用字符串表示，则应当返回null。
    SimpleGrantedAuthority:为Authentication存放一个代表权限的字符串.
    ...
AuthenticationManager:(接口)处理一个Authentication request， Authentication authenticate(Authentication authentication)
    ProviderManager：通过AuthenticationProvider列表来处理认证请求，List<AuthenticationProvider> getProviders()  
                        authenticate(Authentication authentication) 
AuthenticationProvider:(接口)
    DaoAuthenticationProvider：从UserDetailsService获取一个user,getUserDetailsService(),
                    retrieveUser(String username, UsernamePasswordAuthenticationToken authentication)


异常相关：
AuthenticationException：

AuthenticationServiceException
过滤器相关：
Filter(javax.servlet):void doFilter(ServletRequest request, ServletResponse response, FilterChain chain)  
    GenericFilterBean
        DelegatingFilterProxy:
        OncePerRequestFilter:
        FilterChainProxy:
        AbstractAuthenticationProcessingFilter： attemptAuthentication (request,response),getFailureHandler(),getSuccessHandler() 
                            successfulAuthentication(),unsuccessfulAuthentication()
            CasAuthenticationFilter,
            OpenIDAuthenticationFilter
            UsernamePasswordAuthenticationFilter:getPasswordParameter() ,getUsernameParameter() ,obtainPassword( request) ,setDetails()
        ExceptionTranslationFilter：Handles any AccessDeniedException and AuthenticationException thrown within the filter chain. 
        ConcurrentSessionFilter:determineExpiredUrl(HttpServletRequest request, SessionInformation info) 

Hander相关：
AuthenticationSuccessHandler:(接口):onAuthenticationSuccess(request,response,authentication)
    ForwardAuthenticationSuccessHandler:
    SavedRequestAwareAuthenticationSuccessHandler:
    SimpleUrlAuthenticationSuccessHandler:
 
Event相关：
InteractiveAuthenticationSuccessEvent 
入口：
AuthenticationEntryPoint：
    LoginUrlAuthenticationEntryPoint：UsernamePasswordAuthenticationFilter使用ExceptionTranslationFilter来重定向到登录页面
     commence (request,response,authException)重定向方法，getLoginFormUrl() 
Listener相关:
javax.servlet.http.HttpSessionListener
    HttpSessionEventPublisher: sessionCreated(javax.servlet.http.HttpSessionEvent event), 
                                    sessionDestroyed(javax.servlet.http.HttpSessionEvent event) 
Session相关：                                
SessionRegistry:(接口)：getAllPrincipals() getAllSessions(), getSessionInformation(),registerNewSession()
    SessionRegistryImpl:
SessionAuthenticationStrategy:(接口)A 
    CompositeSessionAuthenticationStrategySessionAuthenticationStrategy that accepts multiple SessionAuthenticationStrategy 
                implementations to delegate to. Each SessionAuthenticationStrategy is invoked in turn. The invocations are short circuited if any exception, (i.e. SessionAuthenticationException) is thrown. 
    ConcurrentSessionControlAuthenticationStrategy：控制用户可以同时登录的数量，就是控制一个用户可以同时创建几个session
    SessionFixationProtectionStrategy：防止会话固定攻击
    RegisterSessionAuthenticationStrategy:register a user with the SessionRegistry after successful Authentication. 
匿名认证相关：
AuthenticationProvider
    AnonymousAuthenticationProvider：authenticate(Authentication authentication), getKey()  
Authentication:
    AnonymousAuthenticationToken:Represents an anonymous Authentication,getPrincipal() 
GenericFilterBean
    AnonymousAuthenticationFilter: createAuthentication(HttpServletRequest request)  
    


public String getCurrentUsername() 
{

      Object principal = SecurityContextHolder.getContext().getAuthentication().getPrincipal();

      if (principal instanceof UserDetails) 
      {

         return ((UserDetails) principal).getUsername();

      }

      if (principal instanceof Principal) 
      {

         return ((Principal) principal).getName();

      }

      return String.valueOf(principal);

}