2 Samuel 22:21

according to my righteousness This is no vain-glorious boasting of his own merits, but a testimony to the faithfulness of Jehovah to guard and reward His faithful servants. David does not lay claim to a perfect righteousness, but to sincerity and single-heartedness in his devotion to God. Compare his own testimony (1 Samuel 26:23), God's testimony (1 Kings 14:8), and the testimony of history (1 Kings 11:4; 1 Kings 15:5), to his essential integrity.

Is not this conscious rectitude, this "princely heart of innocence," a clear indication that the Psalm was written before his great fall?

the cleanness of my hands = the purity of my actions. Cp. Psalms 24:4.