RequestLimiter.java

import android.util.Log;
import java.util.Arrays;

/**
 * Sample usage:
 *
 * class MyApp extends Application {
 *      private Api sApi;
 *      private RequestLimiter sRequestlimiter = new RequestLimiter(5, 1000);
 *
 *      public static synchronized Api api() {
 *          if (sApi == null) {
 *              sApi = new Api();
 *          }
 *
 *          sRequestLimiter.nextRequest();
 *          return sApi;
 *      }
 *
 *      public static Api apiWithoutRequest() {
 *          return sApi;
 *      }
 * }
 *
 * @author Roland Schilter <roli@schilter.me>
 */
public class RequestLimiter {

    protected int mRateLimitCount;
    protected int mRateLimitMillis;

    protected long[] mRequestTimes;

    /**
     * Index of last recorded time
     */
    protected int mRequestIndex = 0;
    protected long mRequestCount = 0;

    /**
     * @param rateLimitCount    How many requests
     * @param rateLimitMillis   In how much time
     */
    public RequestLimiter(int rateLimitCount, int rateLimitMillis) {
        mRateLimitCount = rateLimitCount;
        mRateLimitMillis = rateLimitMillis;
        mRequestTimes = new long[rateLimitCount];
        Arrays.fill(mRequestTimes, 0);
    }

    /**
     * In case of limit exceedance we wait the required time and then record this request
     */
    public void nextRequest() {
        waitRequest();
        recordRequest();
    }

    protected void recordRequest() {
        mRequestIndex = (mRequestIndex + 1) % mRateLimitCount;
        mRequestTimes[mRequestIndex] = System.currentTimeMillis();
        mRequestCount += 1;
    }

    protected void waitRequest() {
        // verify that time since oldest request is more than rateLimitSeconds
        int oldestIndex = (mRequestIndex + 1) % mRateLimitCount;
        long sinceOldestRequest = System.currentTimeMillis() - mRequestTimes[oldestIndex];

        // if time since oldest request (keeping only track of rate limited count times) is longer than
        // the rate limit then we exceeded it
        if (sinceOldestRequest < mRateLimitMillis) {
            long pause = mRateLimitMillis - sinceOldestRequest;
            Log.i(getClass().getName(), "Rate limit exceeded, pausing for " + pause + "ms");

            if (pause > mRateLimitMillis) {
                // somebody must have been screwing with the date/time on the phone
                // just wait the max time and reset times
                Arrays.fill(mRequestTimes, 0);
                pause = mRateLimitMillis;
            }

            try {
                Thread.sleep(pause);
            } catch (InterruptedException ex) {
                Thread.currentThread().interrupt();
            }
        }
    }

}