这篇文章给大家介绍SpringSecurity默认表单登录页展示流程源码是怎样的，内容非常详细，感兴趣的小伙伴们可以参考借鉴，希望对大家能有所帮助。

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 1.准备工作（体验SpringSecurity默认表单认证）

  1.1 创建SpringSecurity项目

  先通过IDEA 创建一个SpringBoot项目 并且依赖SpringSecurity，Web依赖

  此时pom.xml会自动添加

org.springframework.boot spring-boot-starter-security

  1.2 提供一个接口

@RestControllerpublic class HelloController {@RequestMapping("/hello")public String hello() { return "Hello SpringSecurity"; }}

，

  1.3 启动项目

  直接访问 提供的接口

http://localhost:8080/hello

  会发现浏览器被直接重定向到了 /login 并且显示如下默认的表单登录页

http://localhost:8080/login

  1.4 登录

  在启动项目的时候 控制台会打印一个 seuciryt password ： xxx

Using generated security password: f520875f-ea2b-4b5d-9b0c-f30c0c17b90b

  直接登录

用户名：user 密码 ：f520875f-ea2b-4b5d-9b0c-f30c0c17b90b

  登录成功并且 浏览器又会重定向到 刚刚访问的接口

 2.springSecurityFilterchain 过滤器链

 如果你看过我另一篇关于SpringSecurity初始化源码的博客，那么你一定知道当SpringSecurity项目启动完成后会初始化一个 springSecurityFilterchain 它内部 additionalFilters属性初始化了很多Filter 如下所有的请求都会经过这一系列的过滤器 Spring Security就是通过这些过滤器 来进行认证授权等

 3.FilterSecurityInterceptor （它会判断这次请求能否通过）

 FilterSecurityInterceptor是过滤器链中最后一个过滤器，主要用于判断请求能否通过，内部通过AccessDecisionManager 进行投票判断

 当我们未登录访问

http://localhost:8080/hello

 请求会被 FilterSecurityInterceptor 拦截

public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException, ServletException { FilterInvocation fi = new FilterInvocation(request, response, chain); invoke(fi);}

 重点看invoke方法

public void invoke(FilterInvocation fi) throws IOException, ServletException { if ((fi.getRequest() != null)  && (fi.getRequest().getAttribute(FILTER_APPLIED) != null)  && observeOncePerRequest) { // filter already applied to this request and user wants us to observe // once-per-request handling, so don't re-do security checking fi.getChain().doFilter(fi.getRequest(), fi.getResponse()); } else { // first time this request being called, so perform security checking if (fi.getRequest() != null && observeOncePerRequest) {  fi.getRequest().setAttribute(FILTER_APPLIED, Boolean.TRUE); } InterceptorStatusToken token = super.beforeInvocation(fi); try {  fi.getChain().doFilter(fi.getRequest(), fi.getResponse()); } finally {  super.finallyInvocation(token); } super.afterInvocation(token, null); }}

 源码中有这样一句，其实就是判断当前用户是否能够访问指定的接口，可以则执行 fi.getChain().doFilter 调用访问的接口否则 内部会抛出异常

InterceptorStatusToken token = super.beforeInvocation(fi);

 beforeInvocation 方法内部是通过 accessDecisionManager 去做决定的 Spring Security已经内置了几个基于投票的AccessDecisionManager包括（AffirmativeBased ，ConsensusBased ，UnanimousBased）当然如果需要你也可以实现自己的AccessDecisionManager

 使用这种方式，一系列的AccessDecisionVoter将会被AccessDecisionManager用来对Authentication是否有权访问受保护对象进行投票，然后再根据投票结果来决定是否要抛出AccessDeniedException

this.accessDecisionManager.decide(authenticated, object, attributes);

 AffirmativeBased的 decide的实现如下

public void decide(Authentication authentication, Object object, Collection configAttributes) throws AccessDeniedException { int deny = 0; Iterator var5 = this.getDecisionVoters().iterator(); while(var5.hasNext()) { AccessDecisionVoter voter = (AccessDecisionVoter)var5.next(); int result = voter.vote(authentication, object, configAttributes); if (this.logger.isDebugEnabled()) {  this.logger.debug("Voter: " + voter + ", returned: " + result); } switch(result) { case -1:  ++deny;  break; case 1:  return; } } if (deny > 0) { throw new AccessDeniedException(this.messages.getMessage("AbstractAccessDecisionManager.accessDenied", "Access is denied")); } else { this.checkAllowIfAllAbstainDecisions(); }}

 AffirmativeBased的逻辑是这样的：

（1）只要有AccessDecisionVoter的投票为ACCESS_GRANTED则同意用户进行访问；（2）如果全部弃权也表示通过；（3）如果没有一个人投赞成票，但是有人投反对票，则将抛出AccessDeniedException。

 当我们第一次访问的时候

http://localhost:8080/hello的时候

 返回 result = -1 会抛出 AccessDeniedException 拒绝访问异常

 4.ExceptionTranslationFilter （捕获AccessDeniedException异常）

 该过滤器它会接收到FilterSecurityInterceptor抛出的 AccessDeniedException异常）并且进行捕获，然后发送重定向到/login请求

 源码如下：

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); logger.debug("Chain processed normally"); } catch (IOException ex) { throw ex; } catch (Exception ex) { // Try to extract a SpringSecurityException from the stacktrace Throwable[] causeChain = throwableAnalyzer.determineCauseChain(ex); RuntimeException ase = (AuthenticationException) throwableAnalyzer  .getFirstThrowableOfType(AuthenticationException.class, causeChain); if (ase == null) {  ase = (AccessDeniedException) throwableAnalyzer.getFirstThrowableOfType(   AccessDeniedException.class, causeChain); } if (ase != null) {  if (response.isCommitted()) {  throw new ServletException("Unable to handle the Spring Security Exception because the response is already committed.", ex);  }  handleSpringSecurityException(request, response, chain, ase); } else {  // Rethrow ServletExceptions and RuntimeExceptions as-is  if (ex instanceof ServletException) {  throw (ServletException) ex;  }  else if (ex instanceof RuntimeException) {  throw (RuntimeException) ex;  }  // Wrap other Exceptions. This shouldn't actually happen  // as we've already covered all the possibilities for doFilter  throw new RuntimeException(ex); } }}

 当获取异常后 调用

handleSpringSecurityException(request, response, chain, ase);

 handleSpringSecurityException 源码如下：

private void handleSpringSecurityException(HttpServletRequest request, HttpServletResponse response, FilterChain chain, RuntimeException exception) throws IOException, ServletException { if (exception instanceof AuthenticationException) { logger.debug(  "Authentication exception occurred; redirecting to authentication entry point",  exception); sendStartAuthentication(request, response, chain,  (AuthenticationException) exception); } else if (exception instanceof AccessDeniedException) { Authentication authentication = SecurityContextHolder.getContext().getAuthentication(); if (authenticationTrustResolver.isAnonymous(authentication) || authenticationTrustResolver.isRememberMe(authentication)) {  logger.debug(   "Access is denied (user is " + (authenticationTrustResolver.isAnonymous(authentication) ? "anonymous" : "not fully authenticated") + "); redirecting to authentication entry point",   exception);  sendStartAuthentication(   request,   response,   chain,   new InsufficientAuthenticationException(   messages.getMessage(    "ExceptionTranslationFilter.insufficientAuthentication",    "Full authentication is required to access this resource"))); } else {  logger.debug(   "Access is denied (user is not anonymous); delegating to AccessDeniedHandler",   exception);  accessDeniedHandler.handle(request, response,   (AccessDeniedException) exception); } }}

 先判断获取的异常是否是AccessDeniedException 再判断是否是匿名用户，如果是则调用 sendStartAuthentication 重定向到登录页面

 重定向登录页面之前会保存当前访问的路径，这就是为什么我们访问 /hello接口后 再登录成功后又会跳转到 /hello接口，因为在重定向到/login接口前 这里进行了保存 requestCache.saveRequest(request, response);

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 SecurityContextHolder.getContext().setAuthentication(null); requestCache.saveRequest(request, response); logger.debug("Calling Authentication entry point."); authenticationEntryPoint.commence(request, response, reason);}

 authenticationEntryPoint.commence(request, response, reason);方法内部

 调用LoginUrlAuthenticationEntryPoint 的 commence方法

 LoginUrlAuthenticationEntryPoint 的commence方法内部有 构造重定向URL的方法

redirectUrl = buildRedirectUrlToLoginPage(request, response, authException);protected String buildRedirectUrlToLoginPage(HttpServletRequest request, HttpServletResponse response, AuthenticationException authException) { String loginForm = determineUrlToUseForThisRequest(request, response,  authException);protected String determineUrlToUseForThisRequest(HttpServletRequest request, HttpServletResponse response, AuthenticationException exception) { return getLoginFormUrl();}

 最终会获取到需要重定向的URL /login

 然后sendRedirect 既会重定向到 /login 请求

 5.DefaultLoginPageGeneratingFilter （会捕获重定向的/login 请求）

 DefaultLoginPageGeneratingFilter是过滤器链中的一个用于捕获/login请求,并且渲染出一个默认表单页面

public void doFilter(ServletRequest req, ServletResponse res, FilterChain chain) throws IOException, ServletException { HttpServletRequest request = (HttpServletRequest) req; HttpServletResponse response = (HttpServletResponse) res; boolean loginError = isErrorPage(request); boolean logoutSuccess = isLogoutSuccess(request); if (isLoginUrlRequest(request) || loginError || logoutSuccess) { String loginPageHtml = generateLoginPageHtml(request, loginError,  logoutSuccess); response.setContentType("text/html;charset=UTF-8"); response.setContentLength(loginPageHtml.getBytes(StandardCharsets.UTF_8).length); response.getWriter().write(loginPageHtml); return; } chain.doFilter(request, response);}

 isLoginUrlRequest 判断请求是否是 loginPageUrl

private boolean isLoginUrlRequest(HttpServletRequest request) { return matches(request, loginPageUrl);}

 因为我们没有配置所以 默认的 loginPageUrl = /login

 验证通过请求路径 能匹配 loginPageUrl

String loginPageHtml = generateLoginPageHtml(request, loginError,  logoutSuccess);

 generateLoginPageHtml 绘制默认的HTML 页面，到此我们默认的登录页面怎么来的就解释清楚了

private String generateLoginPageHtml(HttpServletRequest request, boolean loginError,  boolean logoutSuccess) { String errorMsg = "Invalid credentials"; if (loginError) {  HttpSession session = request.getSession(false);  if (session != null) {   AuthenticationException ex = (AuthenticationException) session     .getAttribute(WebAttributes.AUTHENTICATION_EXCEPTION);   errorMsg = ex != null ? ex.getMessage() : "Invalid credentials";  } } StringBuilder sb = new StringBuilder(); sb.append("\n"   + "\n"   + " \n"   + " \n"   + " \n"   + " \n"   + " \n"   + " \n"   + " \n"   + " \n"   + " \n"   + " \n"   + "  

\n"); String contextPath = request.getContextPath(); if (this.formLoginEnabled) {  sb.append("  

\n"    + "  

Please sign in

\n"    + createError(loginError, errorMsg)    + createLogoutSuccess(logoutSuccess)    + "  

\n"    + "   Username\n"    + "   \n"    + "  

\n"    + "  

\n"    + "   Password\n"    + "   \n"    + "  

\n"    + createRememberMe(this.rememberMeParameter)    + renderHiddenInputs(request)    + "  Sign in\n"    + "  

\n"); } if (openIdEnabled) {  sb.append("  

\n"    + "  

Login with OpenID Identity

\n"    + createError(loginError, errorMsg)    + createLogoutSuccess(logoutSuccess)    + "  

\n"    + "   Identity\n"    + "   \n"    + "  

\n"    + createRememberMe(this.openIDrememberMeParameter)    + renderHiddenInputs(request)    + "  Sign in\n"    + "  

\n"); } if (oauth3LoginEnabled) {  sb.append("

Login with OAuth 2.0

");  sb.append(createError(loginError, errorMsg));  sb.append(createLogoutSuccess(logoutSuccess));  sb.append("\n");  for (Map.Entry clientAuthenticationUrlToClientName : oauth3AuthenticationUrlToClientName.entrySet()) {   sb.append(" \n");  }  sb.append("

");   String url = clientAuthenticationUrlToClientName.getKey();   sb.append("");   String clientName = HtmlUtils.htmlEscape(clientAuthenticationUrlToClientName.getValue());   sb.append(clientName);   sb.append("");   sb.append("

\n"); } if (this.saml2LoginEnabled) {  sb.append("

Login with SAML 2.0

");  sb.append(createError(loginError, errorMsg));  sb.append(createLogoutSuccess(logoutSuccess));  sb.append("\n");  for (Map.Entry relyingPartyUrlToName : saml2AuthenticationUrlToProviderName.entrySet()) {   sb.append(" \n");  }  sb.append("

");   String url = relyingPartyUrlToName.getKey();   sb.append("");   String partyName = HtmlUtils.htmlEscape(relyingPartyUrlToName.getValue());   sb.append(partyName);   sb.append("");   sb.append("

\n"); } sb.append("

\n"); sb.append(""); return sb.toString();}

至此 SpringSecurity 默认表单登录页展示流程源码部分已经全部讲解完毕，会渲染出下面的页面，但是一定要有网的情况，否则样式可能会变化

6.总结

本篇主要讲解 SpringSecurity提供的默认表单登录页 它是如何展示的的流程，包括涉及这一流程中相关的 3个过滤器

1.FilterSecurityInterceptor，2.ExceptionTranslationFilter ，3.DefaultLoginPageGeneratingFilter 过滤器，并且简单介绍了一下 AccessDecisionManager 它主要进行投票来判断该用户是否能够访问相应的 资源AccessDecisionManager 投票机制我也没有深究 后续我会详细深入一下再展开

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