CE-604 expose fetching MemoizedResult (so nulls can be cached and differentiated from not-founds)

qqq-backend-core/src/main/java/com/kingsrook/qqq/backend/core/utils/memoization/Memoization.java

@@ -67,7 +67,26 @@ public class Memoization<K, V>
       {
          if(result.getTime().isAfter(Instant.now().minus(timeout)))
          {
-            return (Optional.of(result.getResult()));
+            return (Optional.ofNullable(result.getResult()));
+         }
+      }
+
+      return (Optional.empty());
+   }
+
+
+
+   /*******************************************************************************
+    **
+    *******************************************************************************/
+   public Optional<MemoizedResult<V>> getMemoizedResult(K key)
+   {
+      MemoizedResult<V> result = map.get(key);
+      if(result != null)
+      {
+         if(result.getTime().isAfter(Instant.now().minus(timeout)))
+         {
+            return (Optional.ofNullable(result));
          }
       }
 
@@ -122,6 +141,16 @@ public class Memoization<K, V>
 
 
 
+   /*******************************************************************************
+    **
+    *******************************************************************************/
+   public void clear()
+   {
+      this.map.clear();
+   }
+
+
+
    /*******************************************************************************
     ** Setter for timeoutSeconds
     **

qqq-backend-core/src/main/java/com/kingsrook/qqq/backend/core/utils/memoization/MemoizedResult.java

@@ -29,7 +29,7 @@ import java.time.Instant;
  ** Object stored in the Memoization class.  Shouldn't need to be visible outside
  ** its package.
  *******************************************************************************/
-class MemoizedResult<T>
+public class MemoizedResult<T>
 {
    private T       result;
    private Instant time;

qqq-backend-core/src/test/java/com/kingsrook/qqq/backend/core/utils/memoization/MemoizationTest.java

@@ -26,6 +26,7 @@ import java.time.Duration;
 import java.util.ArrayList;
 import java.util.Iterator;
 import java.util.List;
+import java.util.Optional;
 import java.util.concurrent.ExecutionException;
 import java.util.concurrent.ExecutorService;
 import java.util.concurrent.Executors;
@@ -36,6 +37,9 @@ import com.kingsrook.qqq.backend.core.utils.SleepUtils;
 import org.junit.jupiter.api.Disabled;
 import org.junit.jupiter.api.Test;
 import static org.assertj.core.api.Assertions.assertThat;
+import static org.junit.jupiter.api.Assertions.assertNotNull;
+import static org.junit.jupiter.api.Assertions.assertNull;
+import static org.junit.jupiter.api.Assertions.assertTrue;
 
 
 /*******************************************************************************
@@ -84,6 +88,40 @@ class MemoizationTest extends BaseTest
 
 
 
+   /*******************************************************************************
+    **
+    *******************************************************************************/
+   @Test
+   void testCanStoreNull()
+   {
+      Memoization<String, Integer> memoization = new Memoization<>();
+      memoization.storeResult("null", null);
+
+      ///////////////////////////////////////////////////////////////////////////////////////////
+      // note - we can't tell a stored null apart from a non-stored value by calling getResult //
+      ///////////////////////////////////////////////////////////////////////////////////////////
+      Optional<Integer> optionalNull = memoization.getResult("null");
+      assertNotNull(optionalNull);
+      assertTrue(optionalNull.isEmpty());
+
+      ////////////////////////////////////////////
+      // instead, we must use getMemoizedResult //
+      ////////////////////////////////////////////
+      Optional<MemoizedResult<Integer>> optionalMemoizedResult = memoization.getMemoizedResult("null");
+      assertNotNull(optionalMemoizedResult);
+      assertTrue(optionalMemoizedResult.isPresent());
+      assertNull(optionalMemoizedResult.get().getResult());
+
+      /////////////////////////////////////////////////////////////////
+      // make sure getMemoizedResult returns empty for an un-set key //
+      /////////////////////////////////////////////////////////////////
+      optionalMemoizedResult = memoization.getMemoizedResult("never-stored");
+      assertNotNull(optionalMemoizedResult);
+      assertTrue(optionalMemoizedResult.isEmpty());
+   }
+
+
+
    /*******************************************************************************
     **
     *******************************************************************************/