springboot+shiro+ajax 角色的权限不足时 返回 No message available

Question

demo使用springboot+shiro做权限管理，使用ajax操作json做数据交换。在ShiroConfig中在资源上增加角色的配置

@Configuration
public class ShiroConfig {

    @Bean
    public CustomRealm getCustomRealm() {
        return new CustomRealm();
    }

    @Bean
    public DefaultWebSecurityManager getSecurityManager() {
        DefaultWebSecurityManager sm = new DefaultWebSecurityManager();
        sm.setRealm(getCustomRealm());
        return sm;
    }

    @Bean
    public ShiroFilterFactoryBean getShiroFilterFactoryBean(
        DefaultWebSecurityManager securityManager) {

        ShiroFilterFactoryBean shirofilterfactorybean = new ShiroFilterFactoryBean();

        shirofilterfactorybean.setSecurityManager(securityManager);

        shirofilterfactorybean.setLoginUrl("/index.html");
        shirofilterfactorybean.setSuccessUrl("/home");
        //        shirofilterfactorybean.setUnauthorizedUrl("/error");

        // 配置数据库中的resource
        Map<String, String> filterChainDefinitionMap =  new LinkedHashMap<>();

        filterChainDefinitionMap.put("/emp/**", "authc,roles[test]");
        filterChainDefinitionMap.put("/home", "authc");
        filterChainDefinitionMap.put("/logout", "logout");

        shirofilterfactorybean.setFilterChainDefinitionMap(filterChainDefinitionMap);

        // 覆盖默认shiro拦截器
        Map<String, Filter> filters = new LinkedHashMap<>();
        filters.put("authc", new SessionFilter());
        shirofilterfactorybean.setFilters(filters);
        return shirofilterfactorybean;
    }
}

用户：admin，对应的角色名：admin。使用用户 admin 登录后，ajax的error方法得到的内容为：

Whitelabel Error Page
=====================

This application has no explicit mapping for /error, so you are seeing this as a fallback.

Mon May 25 16:50:38 CST 2020

There was an unexpected error (type=Unauthorized, status=401).

No message available

其实设置过全局的异常处理，但是debug的时候发现并没有走这段代码：

@ExceptionHandler({UnknownAccountException.class})
@ResponseBody
public ResultBean<String> unknownAccountHandler(HttpServletRequest request, Exception exception) throws Exception {
    return ResultBean.error(500 , "请检查账号或密码");
}

@ExceptionHandler({LockedAccountException.class})
@ResponseBody
public ResultBean<String> lockedAccountExceptionHandler(HttpServletRequest request, Exception exception) throws Exception {
    return ResultBean.error(500 , "账号被锁定，请联系管理员");
}

@ExceptionHandler({UnauthorizedException.class , AuthorizationException.class , ShiroException.class})
@ResponseBody
public ResultBean<String> unauthorizedHandler(HttpServletRequest request, Exception exception) throws Exception {
    return ResultBean.error(500 , "您的权限不足");
}

@ExceptionHandler({UnauthenticatedException.class})
@ResponseBody
public ResultBean<String> unauthenticatedHandler(HttpServletRequest request, Exception exception) throws Exception {
    return ResultBean.error(500 , "未授权");
}

页面的ajax代码：

$.ajax({
                type: "GET",
                url: "./emp/search",
                data: param,
                dataType: "json",
                contentType: "application/json;charset=utf-8",
                success: function (result) {
                    layui.use(['laypage', 'layer'], function() {
                        let laypage = layui.laypage
                        let data = result.data
                        //总页数大于页码总数
                        laypage.render({
                            elem: 'demo1'  ,
                            pages: data.pages,      //通过后台拿到的总页数
                            count: data.total,      //数据总数
                            curr: data.pageNum,     //初始化当前页
                            limit: data.pageSize,
                            jump: function (obj , first) {
                                if( !first) {
                                    getData( obj.curr )
                                }
                            }
                        })
                        displayDataList( data.list )
                    } )
                }, error: function (xhr) {
                    let obj = JSON.parse(xhr.responseText)
                    layer.msg( obj.message )
                }

请大家指教，应该如何处理