​ 本文基于 spring boot starter security 2.2.1.RELEASE

不多BB，先看安全配置类

@Configuration
@EnableWebSecurity
@EnableGlobalMethodSecurity(prePostEnabled = true, securedEnabled = true)
public class CloudSimpleSecurityConfig extends WebSecurityConfigurerAdapter {
    
    // .... 省略部分配置代码

    @Override
    public void configure(WebSecurity web) throws Exception {
        web.ignoring()
                .antMatchers(HttpMethod.OPTIONS, "/**");
    }

    @Override
    public void configure(HttpSecurity http) throws Exception {
        http
                .csrf()
                .disable()
                .and()
                .headers()
                .frameOptions()
                .disable()
                .and()
                .sessionManagement()
                .sessionCreationPolicy(SessionCreationPolicy.STATELESS)
                .and()
                .authorizeRequests()
                .antMatchers("/api/**").authenticated()
                .and();
    }
}

这里没有开启formLogin功能，是个标准的Restful like 服务提供者。如果我们自定义了某些 Filter，在Filter里面提供了一些自定义的认证方式，然后抛出了一些自定义的异常，怎么返回给前端呢。先看 Filter

public class AuthenticationFilter extends GenericFilterBean {

    @Override
    public void doFilter(ServletRequest servletRequest, ServletResponse servletResponse, FilterChain filterChain) throws CustomeException {  // 抛出自定义的业务异常
        HttpServletRequest httpServletRequest = (HttpServletRequest) servletRequest;
        String url = httpServletRequest.getRequestURI();
        log.info("请求路径: {}", url);
        // 从头中获取token信息并进行认证授权流程
        attemptAuthentication(httpServletRequest, MicroConstants.AUTHORIZATION_HEADER);
        filterChain.doFilter(servletRequest, servletResponse);
    }
    
    private void attemptAuthentication(HttpServletRequest request, String header){
        // ....
        setUserInfo("xxx");
    }
  
    public void setUserInfo(UserVO user){
        // 这里将user 信息存入 Security 上下文中实现认证授权流程
    }

}

追踪源码我们可以知道运行过程中的 Filter 链中有一个 ExceptionTranslationFilter 负责处理链中的异常信息的

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);
                }
                // 只有当我们抛出来的异常是 AuthenticationException或AccessDeniedException 的子类的时候，才进这个处理流程
                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);
            }
        }
    }

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);
            }
        }
    }

很明显，我们的自定义异常不可能是 AuthenticationException 或 AccessDeniedException 的子类的，那怎么办，继续往下看，如果都不是，他会直接 throw new RuntimeException(ex) ， 最终会请求 /error 的地址，也就是springboot 默认的那个错误页面，如果不加这个Filter， 我们以往的处理逻辑是在服务内部定义一个全局的异常处理，加上 @RestControllerAdvice 注解就能生效了，像下面这样

@RestControllerAdvice
public class GlobalExceptionHandler {
      /** 自定义业务异常捕获 */
    @ExceptionHandler(CustomException.class)
    public Result handleBusinessException(CustomException e){
        log.error("storage 异常：", e);
        return Result.error(e.getResultCode());  //自定义的异常返回结构，一般都是返回json，也可以是xml
    }
}

但这里就不行了，因为这里抛出的异常是在 @RestControllerAdvice 生效的更前面。也就是还没进入它的处理范畴。所以我们可以这样

@RestController
@RequestMapping("/")
public class FallbackErrorController implements ErrorController {

    public static final String PATH = "/error";

    @Override
    public String getErrorPath() {
        return PATH;
    }

    @GetMapping(value = PATH)
    public Result ok(HttpServletRequest request){
        Throwable e = (Exception) request.getAttribute(RequestDispatcher.ERROR_EXCEPTION);
        if(e instanceof AuthenticationException){
            return Result.error(ResultCode.InvalidCredential);
        }else if(e instanceof CustomException){
            return Result.error(ResultCode.PermissionDenied);
        }else {
            return Result.error(ResultCode.ServiceError);
        }
    }
}

自己定义这个 /error 的 Request Handler， 到这里我们可以从request中捕捉这个异常，然后返回给前端。Over !