Strange Behavior for Spring cache guava TTL config

Question

I have following spring cache config:

spring.cache.guava.spec: expireAfterWrite=1s

Then I have test for it:

@Test
public void test_not_work() {
  callCachedMethod(..);
  sleep(2s);
  callCachedMethod(..);

  expect("real method called TWO times"); 
  // because cache should be expired after 1s
  // It DOESN'T work, real method only called once
}

@Test
public void test_works() {
  callCachedMethod(..);
  sleep(2s);
  callCachedMethod(..);
  sleep(2s);
  callCachedMethod(..);

  expect("real method called THREE times"); 
  // because cache should be expired after 1s
  // IT WORKS!!
}

can someone explain it?

Answer 1

It's because Guava does not ensure the eviction of the values automatically when the timeout value expires.

Per its documentation here:

Caches built with CacheBuilder do not perform cleanup and evict values "automatically," or instantly after a value expires, or anything of the sort. Instead, it performs small amounts of maintenance during write operations, or during occasional read operations if writes are rare.