Spring Security3源码分析-ExceptionTranslationFilter分析

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ExceptionTranslationFilter过滤器对应的类路径为

org.springframework.security.web.access.ExceptionTranslationFilter

从类名就看出这个过滤器用于异常翻译的。但是从这个过滤器在filterchain中的位置来看,它仅仅处于倒数第三的位置(这个filter后面分为是FilterSecurityInterceptor、SwitchUserFilter),所以ExceptionTranslationFilter只能捕获到后面两个过滤器所抛出的异常。

这里需要强调一下,spring security中的异常类基本上都继承RuntimeException。

接着看ExceptionTranslationFilter执行过程


        //doFilter拦截到请求时,不做处理。仅仅处理后面filter所抛出的异常
        public void doFilter(ServletRequest req, ServletResponse res, FilterChain chain)
                throws IOException, ServletException {
            HttpServletRequest request = (HttpServletRequest) req;
            HttpServletResponse response = (HttpServletResponse) res;

            try {
                chain.doFilter(request, response);
            }
            catch (IOException ex) {
                throw ex;
            }
            catch (Exception ex) {
                //这里主要是从异常堆栈中提取SpringSecurityException
                Throwable[] causeChain = throwableAnalyzer.determineCauseChain(ex);
                RuntimeException ase = (AuthenticationException)
                        throwableAnalyzer.getFirstThrowableOfType(AuthenticationException.class, causeChain);

                if (ase == null) {
                    ase = (AccessDeniedException)throwableAnalyzer.getFirstThrowableOfType(AccessDeniedException.class, causeChain);
                }
                //如果提取到安全异常,则进行处理
                if (ase != null) {
                    handleException(request, response, chain, ase);
                } else {
                    //没有安全异常,继续抛出
                    // Rethrow ServletExceptions and RuntimeExceptions as-is
                    if (ex instanceof ServletException) {
                        throw (ServletException) ex;
                    }
                    else if (ex instanceof RuntimeException) {
                        throw (RuntimeException) ex;
                    }
                    throw new RuntimeException(ex);
                }
            }
        }
        //处理安全异常
        private void handleException(HttpServletRequest request, HttpServletResponse response, FilterChain chain,
                RuntimeException exception) throws IOException, ServletException {
            //如果是认证异常,由sendStartAuthentication处理
            if (exception instanceof AuthenticationException) {
                sendStartAuthentication(request, response, chain, (AuthenticationException) exception);
            }
            //如果是访问拒绝异常,由访问拒绝处理类的handle处理
            else if (exception instanceof AccessDeniedException) {
                if (authenticationTrustResolver.isAnonymous(SecurityContextHolder.getContext().getAuthentication())) {
                    sendStartAuthentication(request, response, chain, new InsufficientAuthenticationException(
                            "Full authentication is required to access this resource"));
                }
                else {
                    accessDeniedHandler.handle(request, response, (AccessDeniedException) exception);
                }
            }
        }

先分析如何处理认证异常


        //处理认证异常
        protected void sendStartAuthentication(HttpServletRequest request, HttpServletResponse response, FilterChain chain,
                AuthenticationException reason) throws ServletException, IOException {
            // SEC-112: Clear the SecurityContextHolder's Authentication, as the
            // existing Authentication is no longer considered valid
            //首先把SecurityContext中的认证实体置空
            SecurityContextHolder.getContext().setAuthentication(null);
            //通过cache保存当前的请求信息(分析RequestCacheAwareFilter时再深入)
            requestCache.saveRequest(request, response);
            logger.debug("Calling Authentication entry point.");
            //由认证入口点开始处理
            authenticationEntryPoint.commence(request, response, reason);
        }

这里补充一下

[color=red]authenticationEntryPoint是由配置http标签时,通过什么认证入口来决定注入相应的入口点bean的。请看下面的对应关系列表

form-login认证:LoginUrlAuthenticationEntryPoint

http-basic认证:BasicAuthenticationEntryPoint

openid-login认证:LoginUrlAuthenticationEntryPoint

x509认证:Http403ForbiddenEntryPoint[/color]

就不一一分析每个EntryPoint了,着重看一下LoginUrlAuthenticationEntryPoint


        //主要目的是完成跳转任务
         //创建该bean时,只注入了loginFormUrl属性,其他类变量均为默认值
        public void commence(HttpServletRequest request, HttpServletResponse response, AuthenticationException authException)
                throws IOException, ServletException {
            HttpServletRequest httpRequest = (HttpServletRequest) request;
            HttpServletResponse httpResponse = (HttpServletResponse) response;

            String redirectUrl = null;
            //默认为false
            if (useForward) {
                if (forceHttps && "http".equals(request.getScheme())) {
                    redirectUrl = buildHttpsRedirectUrlForRequest(httpRequest);
                }

                if (redirectUrl == null) {
                    String loginForm = determineUrlToUseForThisRequest(httpRequest, httpResponse, authException);
                    RequestDispatcher dispatcher = httpRequest.getRequestDispatcher(loginForm);
                    dispatcher.forward(request, response);
                    return;
                }
            } else {
                //返回的url为loginFormUrl配置的值,如果未配置,跳转到默认登录页面/spring_security_login
                redirectUrl = buildRedirectUrlToLoginPage(httpRequest, httpResponse, authException);

            }
            redirectStrategy.sendRedirect(httpRequest, httpResponse, redirectUrl);
        }

接着分析访问拒绝类异常的处理过程,看AccessDeniedHandlerImpl的handle方法


        public void handle(HttpServletRequest request, HttpServletResponse response, AccessDeniedException accessDeniedException)
                throws IOException, ServletException {
            if (!response.isCommitted()) {
                //如果配置了access-denied-page属性,跳转到指定的url
                if (errorPage != null) {
                    // Put exception into request scope (perhaps of use to a view)
                    request.setAttribute(SPRING_SECURITY_ACCESS_DENIED_EXCEPTION_KEY, accessDeniedException);

                    // Set the 403 status code.
                    response.setStatus(HttpServletResponse.SC_FORBIDDEN);

                    // forward to error page.
                    RequestDispatcher dispatcher = request.getRequestDispatcher(errorPage);
                    dispatcher.forward(request, response);
                //如果没有配置,则直接响应403禁止访问的错误信息到浏览器端
                } else {
                    response.sendError(HttpServletResponse.SC_FORBIDDEN, accessDeniedException.getMessage());
                }
            }
        }

通过以上分析,可以大体上认识到ExceptionTranslationFilter主要拦截两类安全异常:认证异常、访问拒绝异常。而且仅仅是捕获FilterSecurityInterceptor、SwitchUserFilter以及自定义拦截器的异常。所以在自定义拦截器时,需要注意在链中的顺序。

在上面分析过程中,有requestCache.saveRequest(request, response);的语句,具体requestCache的用途下篇分析。


来源:http://ddrv.cn

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