public function getAdapter()
    {
        if ($this->adapter instanceof Compress\CompressionAlgorithmInterface) {
            return $this->adapter;
        }

        $adapter = $this->adapter;
        $options = $this->getAdapterOptions();
        if (!class_exists($adapter)) {
            $adapter = 'Zend\\Filter\\Compress\\' . ucfirst($adapter);
            if (!class_exists($adapter)) {
                throw new Exception\RuntimeException(sprintf(
                    '%s unable to load adapter; class "%s" not found',
                    __METHOD__,
                    $this->adapter
                ));
            }
        }

        $this->adapter = new $adapter($options);
        if (!$this->adapter instanceof Compress\CompressionAlgorithmInterface) {
            throw new Exception\InvalidArgumentException("Compression adapter '" . $adapter . "' does not implement Zend\\Filter\\Compress\\CompressionAlgorithmInterface");
        }
        return $this->adapter;
    }