Question

We may replace a PHP app with a Java EE app, but the problem is we wanna replace the modules one by one, which means two apps would co-exist and communicate with each other.

So is it possible to share the user session between the 2 apps? Or use a cookie to solve the problem?

Answer 1

Save your session data to a database with session_set_save_handler().

UPDATE
Efficiency wise it would be very mininal, the difference from reading a text file to querying a database (presumably using an existing connection).

Some example code (simplified from what I use)

class Session {
    public function __construct() {
        session_start();       
        $this->clean();        
    }
    public function __destruct() {
        session_write_close();
    }
    public function open() {
        return TRUE;
    }    
    public function close() {
        return TRUE;
    }    
    public function read($id) {
        global $Database;
        if ($Database->select('session_data FROM sessions WHERE session_id="%s"', $id)) {
            list($data) = $Database->fetch(MYSQL_NUM);
            return $data;
        } else {
            return '';
        }
    }    
    public function write($id, $data) {
        global $Database;
        return $Database->replace('sessions SET session_id="%s", session_data="%s", session_updated=%d', array($id, $data, time()));
    }    
    public function destroy($id) {
        global $Database;
        $_SESSION = array();
        return $db->delete('sessions WHERE session_id="%s"', $id);
    }    
    public function clean($expire = 600) {
        global $Database;
        $Database->delete('FROM sessions WHERE session_updated<%d', $time - $expire);
        return TRUE;
    }
}
// Declare the functions to use:
session_set_save_handler(array('Session', 'open'), array('Session', 'close'), array('Session', 'read'), array('Session', 'write'), array('Session', 'destroy'), array('Session', 'clean'));
$Session = new Session;

The you can read/write to the session data using $_SESSION['name'] = data; in the usual technique.