You can configure the PHP environment to store session data in WWDX format http://www.php.net/manual/en/session.configuration.php#ini.session.serialize-handler
session.serialize_handler defines the name of the handler which is used to serialize/deserialize data. Currently, a PHP internal format (name php or php_binary) and WDDX are supported (name wddx). WDDX is only available, if PHP is compiled with WDDX support. Defaults to php.`
About WDDX:
The Web Distributed Data Exchange, or WDDX, is a free, open XML-based technology that allows Web applications created with any platform to easily exchange data with one another over the Web.
and Java WDDX Parser are available through googling :) http://www.google.com.ua/search?q=java+wddx+parser
Of course, this solution is more complicated than just writing a simple parser class - the PHP session format is very simple.
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