google guava cachebuilder use greater of the time between exipreAfterAccess and expireActerWrite

Question

Firstly I apolozige if I didnt adhere to any of the rules and regulations of stackoverflow as I am posting a question for the first time.

I am in a situation where I need to use expirable map where elements from the map can be deleted automatically after certain time. I am glad that i can use cachebuilder from google guava. I need to specify a default time limit which I can do by using expireAfterWrite(..) but I need to override it after my access. I can use exipreAfterAccess(..) but it still removes it after initial time set by exipreAfterWrite(..)

How can I achieve this functionality so that removal criteria checks for greater of the time between exipreAfterAccess and expireActerWrite

Thanks for looking into this

What happens if you don't set `expireAfterWrite`? Doesn't it achieve exactly what you want? — Guillaume Polet, Apr 13 '15 at 21:03
They should be removed after a certain period of time if user havent accessed it — Ricky M, Apr 13 '15 at 21:05
@RickyM: Yes, and they will be, because a write is also an access. — Louis Wasserman, Apr 13 '15 at 21:08
It's unclear what you want to do. How is the map populated to begin with? As the `Loading` prefix suggests, if an entry is not there it will be created for you (using a `CacheLoader`). — fge, Apr 13 '15 at 21:20

score 2 · Accepted Answer · answered Apr 13 '15 at 21:17

I would just advise on not setting the expireAfterWrite value. This will achieve exactly what you want.

See small example below.

It first illustrates your current situation (expireAfterWrite=1 second, expireAfterAccess=2 seconds)--> Every second, value is reloaded
It then creates a cache with only (expireAfterAccess=2 seconds) and accesses it every 100ms-->Value is only loaded once
It then sleeps for 2 seconds-->value is properly reloaded.

import java.util.concurrent.ExecutionException;
import java.util.concurrent.TimeUnit;

import com.google.common.base.Stopwatch;
import com.google.common.cache.CacheBuilder;
import com.google.common.cache.CacheLoader;
import com.google.common.cache.LoadingCache;

public class TestCache {

    private static final String KEY = "Key";

    public static void main(String[] args) throws ExecutionException, InterruptedException {
        CacheLoader<String, String> loader = new CacheLoader<String, String>() {
            @Override
            public String load(String key) throws Exception {
                System.out.println("Loading key");
                return key;
            }
        };
        LoadingCache<String, String> cache1 = CacheBuilder.newBuilder().expireAfterAccess(2L, TimeUnit.SECONDS)
                .expireAfterWrite(1L, TimeUnit.SECONDS).build(loader);
        cache1.get(KEY); // First write
        testCache(cache1);
        LoadingCache<String, String> cache2 = CacheBuilder.newBuilder().expireAfterAccess(2L, TimeUnit.SECONDS).build(loader);
        testCache(cache2);
        System.out.println("Final test on cache 2");
        Thread.sleep(2001);
        System.out.println(cache2.get(KEY));

    }

    private static void testCache(LoadingCache<String, String> cache1) throws ExecutionException, InterruptedException {
        Stopwatch sw = Stopwatch.createStarted();
        while (sw.elapsed(TimeUnit.SECONDS) < 5) {
            System.out.println(sw.elapsed(TimeUnit.MILLISECONDS) + " " + cache1.get(KEY));
            Thread.sleep(100);
        }
    }
}

google guava cachebuilder use greater of the time between exipreAfterAccess and expireActerWrite

1 Answers1