It is important to realize that the moral virtues should not be practiced in isolation from the other moral virtues. Forgiveness and justice should occur side-by-side for you. As you forgive, try to deliberately cultivate a sense of justice or the seeking of what is fair. In this way, your forgiving and becoming less angry should not diminish your quest for justice. In fact, without deep anger, what you seek in justice may be qualitatively different (and actually more fair) than what you seek when fuming with anger.