How to implement Saga? How to do it?

Saga is a pattern for managing distributed transactions, which breaks a large transaction into a series of local transactions, each with a compensating action in case of rollback.

Implementing Saga in Java typically involves:

1. Defining a sequence of steps (local transactions).
2. For each step — implementing the main action and the compensating (undo) action.
3. An orchestrator or choreographer that manages the execution of steps and, in case of an error, triggers compensating actions in reverse order.

An example of a simplified implementation using an interface:

public interface SagaStep {
    void execute() throws Exception;
    void compensate();
}

public class Saga {
    private List<SagaStep> steps = new ArrayList<>();

    public void addStep(SagaStep step) {
        steps.add(step);
    }

    public void execute() {
        List<SagaStep> executedSteps = new ArrayList<>();
        try {
            for (SagaStep step : steps) {
                step.execute();
                executedSteps.add(step);
            }
        } catch (Exception e) {
            // compensate executed steps in reverse order
            for (int i = executedSteps.size() - 1; i >= 0; i--) {
                executedSteps.get(i).compensate();
            }
            throw new RuntimeException("Saga failed and was compensated", e);
        }
    }
}

In real systems, frameworks or message brokers are often used to implement asynchronous and distributed sagas.