Spring Security教程外篇（1）---- AuthenticationException异常详解

这个异常是在登录的时候出现错误时抛出的异常，比如账户锁定，证书失效等，先来看下AuthenticationException常用的的子类：

UsernameNotFoundException 用户找不到

BadCredentialsException 坏的凭据

AccountStatusException 用户状态异常它包含如下子类

AccountExpiredException 账户过期

LockedException 账户锁定

DisabledException 账户不可用

CredentialsExpiredException 证书过期




常见的异常就这几个，还有很多不再一一赘述，仅仅为了展示，对后续的阅读没有什么影响

用户登录验证的过滤器是UsernamePasswordAuthenticationFilter，它继承自AbstractAuthenticationProcessingFilter。

今天研究的是看Spring如何处理AuthenticationException这个异常的，异常的处理一般都是doFilter中处理的，所以首先看AbstractAuthenticationProcessingFilter的doFilter中的代码

    public void doFilter(ServletRequest req, ServletResponse res, FilterChain chain)
            throws IOException, ServletException {

	.......

        try {
            authResult = attemptAuthentication(request, response);
            if (authResult == null) {
                // return immediately as subclass has indicated that it hasn't completed authentication
                return;
            }
            sessionStrategy.onAuthentication(authResult, request, response);
        } catch(InternalAuthenticationServiceException failed) {
            logger.error("An internal error occurred while trying to authenticate the user.", failed);
            unsuccessfulAuthentication(request, response, failed);

            return;
        }catch (AuthenticationException failed) {
            // Authentication failed
            unsuccessfulAuthentication(request, response, failed);

            return;
        }

        ......
    }

从这段代码中我们看到Spring将异常捕获后交给了unsuccessfulAuthentication这个方法来处理（InternalAuthenticationServiceException也是AuthenticationException异常的子类，这是一个内部认证服务异常）

    protected void unsuccessfulAuthentication(HttpServletRequest request, HttpServletResponse response,
            AuthenticationException failed) throws IOException, ServletException {
        SecurityContextHolder.clearContext();

        if (logger.isDebugEnabled()) {
            logger.debug("Authentication request failed: " + failed.toString());
            logger.debug("Updated SecurityContextHolder to contain null Authentication");
            logger.debug("Delegating to authentication failure handler " + failureHandler);
        }

        rememberMeServices.loginFail(request, response);

        failureHandler.onAuthenticationFailure(request, response, failed);
    }

unsuccessfulAuthentication又交给了failureHandler(AuthenticationFailureHandler)来处理，然后追踪failureHandler

private AuthenticationFailureHandler failureHandler = 
	new SimpleUrlAuthenticationFailureHandler();

发现最终是由SimpleUrlAuthenticationFailureHandler这个类的onAuthenticationFailure方法来处理的，打开这个类，有两个核心方法

   public void onAuthenticationFailure(HttpServletRequest request, HttpServletResponse response,
            AuthenticationException exception) throws IOException, ServletException {

        if (defaultFailureUrl == null) {
            logger.debug("No failure URL set, sending 401 Unauthorized error");

            response.sendError(HttpServletResponse.SC_UNAUTHORIZED, "Authentication Failed: " + exception.getMessage());
        } else {
            saveException(request, exception);

            if (forwardToDestination) {
                logger.debug("Forwarding to " + defaultFailureUrl);

                request.getRequestDispatcher(defaultFailureUrl).forward(request, response);
            } else {
                logger.debug("Redirecting to " + defaultFailureUrl);
                redirectStrategy.sendRedirect(request, response, defaultFailureUrl);
            }
        }
    }

    /**
     * Caches the {@code AuthenticationException} for use in view rendering.
     * 

     * If {@code forwardToDestination} is set to true, request scope will be used, otherwise it will attempt to store
     * the exception in the session. If there is no session and {@code allowSessionCreation} is {@code true} a session
     * will be created. Otherwise the exception will not be stored.
     */
    protected final void saveException(HttpServletRequest request, AuthenticationException exception) {
        if (forwardToDestination) {
            request.setAttribute(WebAttributes.AUTHENTICATION_EXCEPTION, exception);
        } else {
            HttpSession session = request.getSession(false);

            if (session != null || allowSessionCreation) {
                request.getSession().setAttribute(WebAttributes.AUTHENTICATION_EXCEPTION, exception);
            }
        }
    }

从onAuthenticationFailure中我们可以看出，如果没有设置defaultFailureUrl就发出401错误。（SC_UNAUTHORIZED是一个常量值是401），如果设置了defaultFailureUrl，调用saveException方法后跳转到defaultFailureUrl页面。

forwardToDestination是是否是服务器跳转，默认使用重定向即客户端跳转。

saveException字面意思是保存异常信息，其实就是把异常信息写入request或者Session中。

如果使用服务器跳转则写入request，客户端跳转则写入Session。

而key是WebAttributes.AUTHENTICATION_EXCEPTION打开WebAttributes找到这个常量

public final class WebAttributes {
  
    public static final String ACCESS_DENIED_403 = "SPRING_SECURITY_403_EXCEPTION";

    public static final String AUTHENTICATION_EXCEPTION = "SPRING_SECURITY_LAST_EXCEPTION";

    public static final String WEB_INVOCATION_PRIVILEGE_EVALUATOR_ATTRIBUTE = 
	WebAttributes.class.getName() + ".WEB_INVOCATION_PRIVILEGE_EVALUATOR_ATTRIBUTE";
}

发现其值为SPRING_SECURITY_LAST_EXCEPTION，这样的话我们就可以在页面上通过el表达式来获取到这个异常了

注意：saveException保存的是Session对象所以直接使用 ${SPRING_SECURITY_LAST_EXCEPTION}是获取不到异常信息的，需要使用${SPRING_SECURITY_LAST_EXCEPTION.message}