MemoizeGuava.java

import com.google.common.cache.CacheBuilder;
import com.google.common.cache.CacheLoader;
import com.google.common.cache.LoadingCache;
import java.util.concurrent.TimeUnit;

public class MemoizeGuava {
        //Memoize example for key value pairs type <String, String>       
       
       //1-Rename the old SLOW function (for example adding  _InnerSlowFunction to its old name)
        static public String getIt_InnerSlowFunction(final String key)  {   
                System.out.println("slow computation/io...");
                //time waste to emulate computing...
                 try{ Thread.sleep(1000);}catch(InterruptedException e){};
                //here you put the slow computation / io
                String strResult = "Resource for "+ key+ " from access : " + key.length(); 
                return strResult;
        }
       
       //2- Replace the original function for this one, the "cached" version
       static public String getIt(final String key){
               return CACHE_TO_MEMOIZE.getUnchecked(key);           
       }
       
       //3- Create the static cache (it can be the step 1, but is here for pedagogical purposes )
        private static final LoadingCache<String, String> CACHE_TO_MEMOIZE = CacheBuilder.newBuilder()
                  .expireAfterWrite(5, TimeUnit.SECONDS)// timeout for valid data expiration
                  .build(CacheLoader.from(MemoizeGuava::getIt_InnerSlowFunction)); //function reference
       
    /**
    * Main test example     
    */
    public static void main(String args[]) throws InterruptedException {                
        System.out.println("get " + getIt("key AA"));
        System.out.println("get " + getIt("key BB"));
        
        //From now on return cache without doing the slow function call..for 5 seconds
        System.out.println("get " + getIt("key AA"));
        System.out.println("get " + getIt("key BB"));
        System.out.println("get " + getIt("key AA"));
        System.out.println("get " + getIt("key BB"));
        
        System.out.println("Waiting...");
       
        Thread.sleep(6000);//wait some time
        
        //Now, cache is gone, we need to go slow again..
        System.out.println("get " + getIt("Key AA"));
        System.out.println("get " + getIt("Key BB"));
    }
}