Java: Dynamic Event Throttling

In the code snippet described below I outline an algorithm for dynamically throttle the number of events occurring. In the example I limit the rate of exceptions being thrown, but theoretically this can be any kind of event, e. g. requests coming from some event source or user.

Throttling / rate limiting for requests (or in this case, exceptions)

    import java.util.Random;

    import org.junit.Test;

    public class Bar {

      private static final long rate = 10L; // ten exceptions allowed
      private static final long per = 60000L; // per minute (= 12.000
                          // milliseconds)
      private static long allowance = rate;
      private static long last = System.currentTimeMillis();

      @Test
      public void testThresholding() {
        // Algorithm adapted from:
        // http://stackoverflow.com/questions/667508/whats-a-good-rate-limiting-algorithm
        for (int i = 0; i < 120; i++) {
          try {
            businessMethod();
          }
          catch (RuntimeException e) {
            long time = System.currentTimeMillis();
            long passedMs = Math.max(time - last, 1);
            last = time;

            double coeff = (double) rate / (double) per;
            long increment = Math.round(passedMs * coeff);

            allowance += increment;

            System.out.printf("-----------------------------\n");
            System.out.printf("time\t\t:%d\n", time);
            System.out.printf("passed (ms)\t:%d\n", passedMs);
            System.out.printf("increment\t:%d\n", increment);
            System.out.printf("allowance\t:%d\n", allowance);

            // Uncomment this block to enable throttling to the
            // defined rate.
            // if (allowance > rate) {
            // allowance = rate; // throttle
            // }
            // System.out.printf("throttled\t:%d\n", allowance);

            if (allowance < 1) {
              System.out.println("==> too many exceptions!");
            }
            else {
              System.out.println("==> still inside the limit.");
              allowance--;
            }

          }
        }
      }

      private void businessMethod() {
        // How many percent of business calls result in an exception
        final int exceptionPercent = 10;

        System.out.println("Business method");

        int val = new Random().nextInt(101);
        int delay = new Random().nextInt(1001);
        try {
          Thread.sleep(delay);
          if (val <= exceptionPercent) {
            throw new RuntimeException("BusinessException");
          }
        }
        catch (InterruptedException e) {
          // ignore
        }
      }
    }