Justice is in making a guilty person get the respective punishment/penalty for the crime done.
The constitution of a country has pre-stated rules and regulations for every act of justice.
Whereas, revenge is a very powerful emotion; there is no limit in taking revenge.
When the one that is victimised feels that the justice been done is not enough and considers the guilty worthy or harsh treatment that is called revenge.
To most revenge takers, it feels satisfying to do bad with the one that did badly to them, as they find it to be their own way of justice.
But, The old law about an eye for an eye leaves everybody blind-Martin Luther King