Memoize in Java with Guava

An example of memoizing, to copy, paste, run, learn, whatever.

Warn

It's supposed you to know what Guava is, what memoize is, when to use, benefits, cons, etc..

Right now, the example

	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"));
	}
	}

view raw MemoizeGuava.java hosted with ❤ by GitHub

Further Reading

Guava Caches Explained
Memoization Wikipedia