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一文搞定 Spring Security 异常处理机制！

今天来和小伙伴们聊一聊 Spring Security 中的异常处理机制。

在 Spring Security 的过滤器链中，ExceptionTranslationFilter 过滤器专门用来处理异常，在 ExceptionTranslationFilter 中，我们可以看到，异常被分为了两大类：认证异常和授权异常，两种异常分别由不同的回调函数来处理，今天松哥就来和大家分享一下这里的条条框框。

1.异常分类

Spring Security 中的异常可以分为两大类，一种是认证异常，一种是授权异常。

认证异常就是 AuthenticationException，它有众多的实现类：

一文搞定 Spring Security 异常处理机制！

可以看到，这里的异常实现类还是蛮多的，都是都是认证相关的异常，也就是登录失败的异常。这些异常，有的松哥在之前的文章中都和大家介绍过了，例如下面这段代码(节选自： Spring Security 做前后端分离，咱就别做页面跳转了！统统 JSON 交互 )：

resp.setContentType("application/json;charset=utf-8");
PrintWriter out = resp.getWriter();
RespBean respBean = RespBean.error(e.getMessage());
if (e instanceof LockedException) {
    respBean.setMsg("账户被锁定，请联系管理员!");
} else if (e instanceof CredentialsExpiredException) {
    respBean.setMsg("密码过期，请联系管理员!");
} else if (e instanceof AccountExpiredException) {
    respBean.setMsg("账户过期，请联系管理员!");
} else if (e instanceof DisabledException) {
    respBean.setMsg("账户被禁用，请联系管理员!");
} else if (e instanceof BadCredentialsException) {
    respBean.setMsg("用户名或者密码输入错误，请重新输入!");
}
out.write(new ObjectMapper().writeValueAsString(respBean));
out.flush();
out.close();

另一类就是授权异常 AccessDeniedException，授权异常的实现类比较少，因为授权失败的可能原因比较少。

一文搞定 Spring Security 异常处理机制！

2.ExceptionTranslationFilter

ExceptionTranslationFilter 是 Spring Security 中专门负责处理异常的过滤器，默认情况下，这个过滤器已经被自动加载到过滤器链中。

有的小伙伴可能不清楚是怎么被加载的，我这里和大家稍微说一下。

当我们使用 Spring Security 的时候，如果需要自定义实现逻辑，都是继承自 WebSecurityConfigurerAdapter 进行扩展，WebSecurityConfigurerAdapter 中本身就进行了一部分的初始化操作，我们来看下它里边 HttpSecurity 的初始化过程：

protected final HttpSecurity getHttp() throws Exception {
    if (http != null) {
        return http;
    }
    AuthenticationEventPublisher eventPublisher = getAuthenticationEventPublisher();
    localConfigureAuthenticationBldr.authenticationEventPublisher(eventPublisher);
    AuthenticationManager authenticationManager = authenticationManager();
    authenticationBuilder.parentAuthenticationManager(authenticationManager);
    Map<Class<?>, Object> sharedObjects = createSharedObjects();
    http = new HttpSecurity(objectPostProcessor, authenticationBuilder,
            sharedObjects);
    if (!disableDefaults) {
        http
            .csrf().and()
            .addFilter(new WebAsyncManagerIntegrationFilter())
            .exceptionHandling().and()
            .headers().and()
            .sessionManagement().and()
            .securityContext().and()
            .requestCache().and()
            .anonymous().and()
            .servletApi().and()
            .apply(new DefaultLoginPageConfigurer<>()).and()
            .logout();
        ClassLoader classLoader = this.context.getClassLoader();
        List<AbstractHttpConfigurer> defaultHttpConfigurers =
                SpringFactoriesLoader.loadFactories(AbstractHttpConfigurer.class, classLoader);
        for (AbstractHttpConfigurer configurer : defaultHttpConfigurers) {
            http.apply(configurer);
        }
    }
    configure(http);
    return http;
}

可以看到，在 getHttp 方法的最后，调用了 configure(http); ，我们在使用 Spring Security 时，自定义配置类继承自 WebSecurityConfigurerAdapter 并重写的 configure(HttpSecurity http) 方法就是在这里调用的，换句话说，当我们去配置 HttpSecurity 时，其实它已经完成了一波初始化了。

在默认的 HttpSecurity 初始化的过程中，调用了 exceptionHandling 方法，这个方法会将 ExceptionHandlingConfigurer 配置进来，最终调用 ExceptionHandlingConfigurer#configure 方法将 ExceptionTranslationFilter 添加到 Spring Security 过滤器链中。

我们来看下 ExceptionHandlingConfigurer#configure 方法源码：

@Override
public void configure(H http) {
    AuthenticationEntryPoint entryPoint = getAuthenticationEntryPoint(http);
    ExceptionTranslationFilter exceptionTranslationFilter = new ExceptionTranslationFilter(
            entryPoint, getRequestCache(http));
    AccessDeniedHandler deniedHandler = getAccessDeniedHandler(http);
    exceptionTranslationFilter.setAccessDeniedHandler(deniedHandler);
    exceptionTranslationFilter = postProcess(exceptionTranslationFilter);
    http.addFilter(exceptionTranslationFilter);
}

可以看到，这里构造了两个对象传入到 ExceptionTranslationFilter 中：

AuthenticationEntryPoint 这个用来处理认证异常。
AccessDeniedHandler 这个用来处理授权异常。

具体的处理逻辑则在 ExceptionTranslationFilter 中，我们来看一下：

public class ExceptionTranslationFilter extends GenericFilterBean {
    public ExceptionTranslationFilter(AuthenticationEntryPoint authenticationEntryPoint,
            RequestCache requestCache) {
        this.authenticationEntryPoint = authenticationEntryPoint;
        this.requestCache = requestCache;
    }
    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) {
            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 {
                if (ex instanceof ServletException) {
                    throw (ServletException) ex;
                }
                else if (ex instanceof RuntimeException) {
                    throw (RuntimeException) ex;
                }
                throw new RuntimeException(ex);
            }
        }
    }
    private void handleSpringSecurityException(HttpServletRequest request,
            HttpServletResponse response, FilterChain chain, RuntimeException exception)
            throws IOException, ServletException {
        if (exception instanceof AuthenticationException) {
            sendStartAuthentication(request, response, chain,
                    (AuthenticationException) exception);
        }
        else if (exception instanceof AccessDeniedException) {
            Authentication authentication = SecurityContextHolder.getContext().getAuthentication();
            if (authenticationTrustResolver.isAnonymous(authentication) || authenticationTrustResolver.isRememberMe(authentication)) {
                sendStartAuthentication(
                        request,
                        response,
                        chain,
                        new InsufficientAuthenticationException(
                            messages.getMessage(
                                "ExceptionTranslationFilter.insufficientAuthentication",
                                "Full authentication is required to access this resource")));
            }
            else {
                accessDeniedHandler.handle(request, response,
                        (AccessDeniedException) exception);
            }
        }
    }
    protected void sendStartAuthentication(HttpServletRequest request,
            HttpServletResponse response, FilterChain chain,
            AuthenticationException reason) throws ServletException, IOException {
        SecurityContextHolder.getContext().setAuthentication(null);
        requestCache.saveRequest(request, response);
        logger.debug("Calling Authentication entry point.");
        authenticationEntryPoint.commence(request, response, reason);
    }
}

ExceptionTranslationFilter 的源码比较长，我这里列出来核心的部分和大家分析：

throwableAnalyzer.getFirstThrowableOfType

AuthenticationEntryPoint 的默认实现类是 LoginUrlAuthenticationEntryPoint，因此默认的认证异常处理逻辑就是 LoginUrlAuthenticationEntryPoint#commence 方法，如下：

public void commence(HttpServletRequest request, HttpServletResponse response,
        AuthenticationException authException) throws IOException, ServletException {
    String redirectUrl = null;
    if (useForward) {
        if (forceHttps && "http".equals(request.getScheme())) {
            redirectUrl = buildHttpsRedirectUrlForRequest(request);
        }
        if (redirectUrl == null) {
            String loginForm = determineUrlToUseForThisRequest(request, response,
                    authException);
            RequestDispatcher dispatcher = request.getRequestDispatcher(loginForm);
            dispatcher.forward(request, response);
            return;
        }
    }
    else {
        redirectUrl = buildRedirectUrlToLoginPage(request, response, authException);
    }
    redirectStrategy.sendRedirect(request, response, redirectUrl);
}

可以看到，就是重定向，重定向到登录页面（即当我们未登录就去访问一个需要登录才能访问的资源时，会自动重定向到登录页面）。

AccessDeniedHandler 的默认实现类则是 AccessDeniedHandlerImpl，所以授权异常默认是在 AccessDeniedHandlerImpl#handle 方法中处理的：

public void handle(HttpServletRequest request, HttpServletResponse response,
        AccessDeniedException accessDeniedException) throws IOException,
        ServletException {
    if (!response.isCommitted()) {
        if (errorPage != null) {
            request.setAttribute(WebAttributes.ACCESS_DENIED_403,
                    accessDeniedException);
            response.setStatus(HttpStatus.FORBIDDEN.value());
            RequestDispatcher dispatcher = request.getRequestDispatcher(errorPage);
            dispatcher.forward(request, response);
        }
        else {
            response.sendError(HttpStatus.FORBIDDEN.value(),
                HttpStatus.FORBIDDEN.getReasonPhrase());
        }
    }
}

可以看到，这里就是服务端跳转返回 403。

3.自定义处理

前面和大家介绍了 Spring Security 中默认的处理逻辑，实际开发中，我们可以需要做一些调整，很简单，在 exceptionHandling 上进行配置即可。

首先自定义认证异常处理类和授权异常处理类：

@Component
public class MyAuthenticationEntryPoint implements AuthenticationEntryPoint {
    @Override
    public void commence(HttpServletRequest request, HttpServletResponse response, AuthenticationException authException) throws IOException, ServletException {
        response.getWriter().write("login failed:" + authException.getMessage());
    }
}
@Component
public class MyAccessDeniedHandler implements AccessDeniedHandler {
    @Override
    public void handle(HttpServletRequest request, HttpServletResponse response, AccessDeniedException accessDeniedException) throws IOException, ServletException {
        response.setStatus(403);
        response.getWriter().write("Forbidden:" + accessDeniedException.getMessage());
    }
}

然后在 SecurityConfig 中进行配置，如下：

@Configuration
public class SecurityConfig extends WebSecurityConfigurerAdapter {
    @Override
    protected void configure(HttpSecurity http) throws Exception {
        http.authorizeRequests()
                ...
                ...
                .and()
                .exceptionHandling()
                .authenticationEntryPoint(myAuthenticationEntryPoint)
                .accessDeniedHandler(myAccessDeniedHandler)
                .and()
                ...
                ...
    }
}

配置完成后，重启项目，认证异常和授权异常就会走我们自定义的逻辑了。