$handler
$handler : string
处理器类名,如果为null则使用默认处理
http 未匹配路由时的处理器
handle(\Psr\Http\Server\RequestHandlerInterface $requesthandler, \Psr\Http\Message\ServerRequestInterface $request, \Psr\Http\Message\ResponseInterface $response)
\Psr\Http\Server\RequestHandlerInterface | $requesthandler | |
\Psr\Http\Message\ServerRequestInterface | $request | |
\Psr\Http\Message\ResponseInterface | $response |