public function setAdapter($adapter)
    {
        if (is_string($adapter)) {
            if (!class_exists($adapter, false)) {
                if (false === strpos($adapter, '_')) {
                    $adapter = 'HTTP_Request2_Adapter_' . ucfirst($adapter);
                }
                if (!class_exists($adapter, false)
                    && preg_match('/^HTTP_Request2_Adapter_([a-zA-Z0-9]+)$/', $adapter)
                ) {
                    include_once str_replace('_', DIRECTORY_SEPARATOR, $adapter) . '.php';
                }
                if (!class_exists($adapter, false)) {
                    throw new HTTP_Request2_LogicException(
                        "Class {$adapter} not found",
                        HTTP_Request2_Exception::MISSING_VALUE
                    );
                }
            }
            $adapter = new $adapter;
        }
        if (!$adapter instanceof HTTP_Request2_Adapter) {
            throw new HTTP_Request2_LogicException(
                'Parameter is not a HTTP request adapter',
                HTTP_Request2_Exception::INVALID_ARGUMENT
            );
        }
        $this->adapter = $adapter;

        return $this;
    }