What is the best way to cache single object within fixed timeout?

Question

Google Guava has CacheBuilder that allows to create ConcurrentHash with expiring keys that allow to remove entries after the fixed tiemout. However I need to cache only one inst

Answer 1

I'd use Guava's Suppliers.memoizeWithExpiration(Supplier delegate, long duration, TimeUnit unit)

public class JdkVersionService {

    @Inject
    private JdkVersionWebService jdkVersionWebService;

    // No need to check too often. Once a year will be good :) 
    private final Supplier latestJdkVersionCache
            = Suppliers.memoizeWithExpiration(jdkVersionSupplier(), 365, TimeUnit.DAYS);


    public JdkVersion getLatestJdkVersion() {
        return latestJdkVersionCache.get();
    }

    private Supplier jdkVersionSupplier() {
        return new Supplier() {
            public JdkVersion get() {
                return jdkVersionWebService.checkLatestJdkVersion();
            }
        };
    }
}

Update with JDK 8

Today, I would write this code differently, using JDK 8 method references and constructor injection for cleaner code:

import java.util.concurrent.TimeUnit;
import java.util.function.Supplier;

import javax.inject.Inject;

import org.springframework.stereotype.Service;

import com.google.common.base.Suppliers;

@Service
public class JdkVersionService {

    private final Supplier latestJdkVersionCache;

    @Inject
    public JdkVersionService(JdkVersionWebService jdkVersionWebService) {
        this.latestJdkVersionCache = Suppliers.memoizeWithExpiration(
                jdkVersionWebService::checkLatestJdkVersion,
                365, TimeUnit.DAYS
        );
    }

    public JdkVersion getLatestJdkVersion() {
        return latestJdkVersionCache.get();
    }
}