如何实现一个以点击次数为值的番石榴缓存？

Question

I'm trying to implement a cache which will count the number of login attempts in the last 5 minutes, in my code i want to check if the user has attempted more than MAX_ATTEMPTS.

In all the code examples i found online for "Guava Cache" use the load method to fetch the value from some other source or calculate it using some method, how can i increment it every time there is a cache hit ?

static LoadingCache<String, Integer> cache = CacheBuilder.newBuilder()
    .maximumSize(100000)
    .expireAfterAccess(5, TimeUnit.MINUTES)
    .build(
            new CacheLoader<String, Integer>() {
                public Integerload(String user) {
                       return ????;
                }
            }
    );

later at runtime i would like to check:

if(cache.getIfPresent(user) != null && cache.get(user) > MAX_ATTEMPTS)

and also increment it if:

if(cache.getIfPresent(user) != null && cache.get(user) <= MAX_ATTEMPTS)

Answer 1

@Oren Your solution isn't thread-safe, since you're operating on a value outside Cache. You'd better use Cache#asMap() view and change value inside ConcurrentMap#compute(K, BiFunction<K, V, V>) method:

forgetPasswordCache.asMap().compute(email, (cachedEmail, currentCount) -> {
  if (currentCount != null && currentCount >= RESET_PASSWORD_MAX_ATTEMPTS) {
    logger.error("User with id: " + user.getId() + " and email: " + email +
         " has reached the maximum number of reset password attempts, the mail will not be sent");
    return null;
  }

  if (currentCount == null) {
    return 1;
  } else {
    return currentCount + 1;
  }
});

Answer 2

You can try and adapt the following snippet:

public class Demo {
    public static void main(String[] x) {
        CacheLoader<String, AtomicInteger> initialValueLoader = new CacheLoader<String, AtomicInteger>() {
            @Override
            public AtomicInteger load(String key) {
                // do not care of the key. everybody starts with 0 login attempts.
                return new AtomicInteger(0);
            }
        };

        LoadingCache<String, AtomicInteger> c = CacheBuilder
            .newBuilder()
            .maximumSize(100000)
            .expireAfterAccess(2, TimeUnit.SECONDS)
            .build(initialValueLoader);

        String user = "bob";

        try {
            // when the user tries to login, increment the attemps by one
            Verify.verify(c.get(user).incrementAndGet() == 1);

            // next call will get one
            Verify.verify(c.get(user).get() == 1);
        } catch (ExecutionException e) {
            throw new RuntimeException("oups: " + e, e);
        }

        // simulate time
        try {
            Thread.sleep(3000);
        } catch (InterruptedException e) {
        }

        // after some time, the cache is cleared
        try {
            Verify.verify(c.get(user).get() == 0);
        } catch (ExecutionException e) {
            throw new RuntimeException("oups: " + e, e);
        }

        System.out.println("done.");
    }
}

Answer 3

SOLVED by using only the Cache functionality of Guava ( without using the loader )

The cache looks like this:

public class ForgetPasswordAttemptsCache {

    private static final Cache<String, Integer> forgetPasswordCache = CacheBuilder.newBuilder()
            .expireAfterAccess(24, TimeUnit.HOURS)
            .build();

    private ForgetPasswordAttemptsCache(){
    }

    public static Cache<String, Integer> getInstance() {
        return forgetPasswordCache;
    }

}

and the use of it:

final String email = user.getEmail();
Integer currentCount = ForgetPasswordAttemptsCache.getInstance().getIfPresent(email);

if (currentCount != null && currentCount >= RESET_PASSWORD_MAX_ATTEMPTS) {
    logger.error("User with id: " + user.getId() + " and email: " + email +
            " has reached the maximum number of reset password attempts, the mail will not be sent");
    return;
}

if (currentCount == null) {
    ForgetPasswordAttemptsCache.getInstance().put(email, new Integer(1));
} else {
    ForgetPasswordAttemptsCache.getInstance().put(email, new Integer(currentCount + 1));
}

Thanks spi for this solution. (now i'm looking for a way to test it without having a test that runs 24 hours.)