ehcache based on date

Question

I'm working with ehcache 2.5.4.

I have an object that needs to be cached through out the day and refreshed with a new value at 00:00am every day.

Currently with ehcache configurations I can only set the time to live and time to idle, but that will depend on the time I created the object or when it's used. ie:

    <cache
    name="cache.expiry.application.date_status"
    maxElementsInMemory="10"
    eternal="false"
    timeToIdleSeconds="60"
    timeToLiveSeconds="50" />

Is there a way to get ehcache to expire specific caches based on specific times.

Answer 1

I've done this by extending Ehcache's Element class like so:

class EvictOnGivenTimestampElement extends Element {

    private static final long serialVersionUID = ...;
    private final long evictOn;

    EvictOnGivenTimestampElement(final Serializable key, final Serializable value, final long evictOn) {
        super(key, value);
        this.evictOn = evictOn;
    }

    @Override
    public boolean isExpired() {
        return System.currentTimeMillis() > evictOn;
    }
}

The rest is as easy as putting new instance of EvictOnGivenTimestampElement object into the cache instead of Element.

Advantage of this approach is that you don't have to worry about external cronjobs, etc. And the obvious disadvantage is the attachment to Ehcache API which I hope won't change too often.

Answer 2

EHCache only supports eviction after a certain period of time (either being in the cache or due to inactivity). However, you should be able to accomplish that fairly easily by scheduling the removal with something like this:

    Timer t = new Timer(true);
    Integer interval = 24 * 60 * 60 * 1000; //24 hours
    Calendar c = Calendar.getInstance();
    c.set(Calendar.HOUR, 0);
    c.set(Calendar.MINUTE, 0);
    c.set(Calendar.SECOND, 0);


    t.scheduleAtFixedRate( new TimerTask() {
            public void run() {
                Cache c = //retrieve cache                  
                c.removeAll();                                            
            }
        }, c.getTime(), interval);

This basic example uses the Java Timer class to illustrate, but any scheduler could be utilized. Every 24 hours, starting from midnight - this would run and remove all the elements from the specified cache. The actual run method could be modified to remove elements matching a certain criteria as well.

You'd just need to make sure you start it when the application is started.

Answer 3

With Ehcache 3.2 I implemented an Expiry extension.

public class EvictAtMidnightExpiry implements Expiry {

    @Override
    public Duration getExpiryForCreation(Object key, Object value) {
        DateTime now = new DateTime();
        DateTime resetAt = now.plusDays(1).withTimeAtStartOfDay();
        long difference = resetAt.toDateTime().getMillis() - now.getMillis();
        return Duration.of(difference, TimeUnit.MILLISECONDS);
    }

    @Override
    public Duration getExpiryForAccess(Object key, ValueSupplier value) {
        return null;
    }

    @Override
    public Duration getExpiryForUpdate(Object key, ValueSupplier oldValue, Object newValue) {
        return null;
    }
}

Now, I have logging etc as well but I minimalized my code for cleanness.

Then you just need to configure it in your configuration builder.

CacheConfigurationBuilder.newCacheConfigurationBuilder(String.class, String.class, ResourcePoolsBuilder.heap(1000)).withExpiry(new EvictAtMidnightExpiry()).build()

Clearly Ehcache improved on there API's somewhat from 2.5 to 3.2 as you don't need to create your own 'element' and ensure it's usage to initiate expiry or eviction policies. The policies are now cache bound.