src/Zend/Filter/Compress.php
public function getAdapter()
    {
        if ($this->_adapter instanceof Zend_Filter_Compress_CompressInterface) {
            return $this->_adapter;
        }

        $adapter = $this->_adapter;
        $options = $this->getAdapterOptions();
        if (!class_exists($adapter)) {

            if (Zend_Loader::isReadable('Zend/Filter/Compress/' . ucfirst($adapter) . '.php')) {
                $adapter = 'Zend_Filter_Compress_' . ucfirst($adapter);
            }
            Zend_Loader::loadClass($adapter);
        }

        $this->_adapter = new $adapter($options);
        if (!$this->_adapter instanceof Zend_Filter_Compress_CompressInterface) {

            throw new Zend_Filter_Exception("Compression adapter '" . $adapter . "' does not implement Zend_Filter_Compress_CompressInterface");
        }
        return $this->_adapter;
    }
public function getAdapter()
    {
        if ($this->_adapter instanceof Zend_Filter_Compress_CompressInterface) {
            return $this->_adapter;
        }

        $adapter = $this->_adapter;
        $options = $this->getAdapterOptions();
        if (!class_exists($adapter)) {

            if (Zend_Loader::isReadable('Zend/Filter/Compress/' . ucfirst($adapter) . '.php')) {
                $adapter = 'Zend_Filter_Compress_' . ucfirst($adapter);
            }
            Zend_Loader::loadClass($adapter);
        }

        $this->_adapter = new $adapter($options);
        if (!$this->_adapter instanceof Zend_Filter_Compress_CompressInterface) {

            throw new Zend_Filter_Exception("Compression adapter '" . $adapter . "' does not implement Zend_Filter_Compress_CompressInterface");
        }
        return $this->_adapter;
    }
Returns the current adapter, instantiating it if necessary

@return string