Circuit Breaker Pattern: An Example

Let's implement a basic Circuit Breaker in Java to illustrate the core algorithm. We won't use any external libraries, just a simple class to demonstrate the state logic:

public class CircuitBreaker {
    private enum State { CLOSED, OPEN, HALF_OPEN }
    private State state = State.CLOSED;
    private int failureCount = 0;
    private final int failureThreshold;
    private final long openTimeout;       // how long to stay open before trying half-open
    private long lastFailureTime = 0;

    public CircuitBreaker(int failureThreshold, long openTimeout) {
        this