protected synchronized MessageDigest getDigest ( ) { if ( this . digest == null ) { try { this . digest = MessageDigest . getInstance ( algorithm ) ; } catch ( NoSuchAlgorithmException e ) { try { this . digest = MessageDigest . getInstance ( DEFAULT_ALGORITHM ) ; } catch ( NoSuchAlgorithmException f ) { this . digest = null ; } } } return ( this . digest ) ; }
Return the MessageDigest object to be used for calculating session identifiers . If none has been created yet initialize one the first time this method is called .