Make DefaultSdkAutoConstructList/Map Serializable.

core/sdk-core/src/main/java/software/amazon/awssdk/core/util/DefaultSdkAutoConstructList.java

@@ -15,6 +15,7 @@
 
 package software.amazon.awssdk.core.util;
 
+import java.io.Serializable;
 import java.util.Collection;
 import java.util.Collections;
 import java.util.Iterator;
@@ -30,7 +31,7 @@
  * @param <T> The element type.
  */
 @SdkProtectedApi
-public final class DefaultSdkAutoConstructList<T> implements SdkAutoConstructList<T> {
+public final class DefaultSdkAutoConstructList<T> implements SdkAutoConstructList<T>, Serializable {
     private static final DefaultSdkAutoConstructList INSTANCE = new DefaultSdkAutoConstructList();
 
     private final List impl = Collections.emptyList();
@@ -173,4 +174,8 @@ public String toString() {
         return impl.toString();
     }
 
+    private Object readResolve() {
+        return getInstance();
+    }
+
 }

core/sdk-core/src/main/java/software/amazon/awssdk/core/util/DefaultSdkAutoConstructMap.java

@@ -15,6 +15,7 @@
 
 package software.amazon.awssdk.core.util;
 
+import java.io.Serializable;
 import java.util.Collection;
 import java.util.Collections;
 import java.util.Map;
@@ -30,7 +31,7 @@
  * @param <V> The value type.
  */
 @SdkProtectedApi
-public final class DefaultSdkAutoConstructMap<K, V> implements SdkAutoConstructMap<K, V> {
+public final class DefaultSdkAutoConstructMap<K, V> implements SdkAutoConstructMap<K, V>, Serializable {
     private static final DefaultSdkAutoConstructMap INSTANCE = new DefaultSdkAutoConstructMap();
 
     private final Map<K, V> impl = Collections.emptyMap();
@@ -117,4 +118,9 @@ public int hashCode() {
     public String toString() {
         return impl.toString();
     }
+
+    private Object readResolve() {
+        return getInstance();
+    }
+
 }

core/sdk-core/src/test/java/software/amazon/awssdk/core/util/DefaultSdkAutoConstructListTest.java

@@ -17,7 +17,13 @@
 
 import static org.assertj.core.api.Assertions.assertThat;
 
+import java.io.ByteArrayInputStream;
+import java.io.ByteArrayOutputStream;
+import java.io.ObjectInputStream;
+import java.io.ObjectOutputStream;
 import java.util.LinkedList;
+import java.util.List;
+import org.junit.jupiter.api.DisplayName;
 import org.junit.jupiter.api.Test;
 
 public class DefaultSdkAutoConstructListTest {
@@ -42,4 +48,32 @@ public void hashCode_sameAsEmptyList() {
     public void toString_emptyList() {
         assertThat(INSTANCE.toString()).isEqualTo("[]");
     }
+
+    @Test
+    @DisplayName("DefaultSdkAutoConstruct is Serializable, and is same instance.")
+    public void serialization_sameSingletonInstance() throws Exception {
+        // Create instance of DefaultSdkAutoConstructList
+        List defaultSdkAutoConstructList = DefaultSdkAutoConstructList.getInstance();
+
+        // Serialize instance into byte array
+        ByteArrayOutputStream baos = new ByteArrayOutputStream();
+        ObjectOutputStream objectOutputStream = new ObjectOutputStream(baos);
+
+        objectOutputStream.writeObject(defaultSdkAutoConstructList);
+        objectOutputStream.flush();
+        objectOutputStream.close();
+
+        // Serialization result
+        byte[] bytes = baos.toByteArray();
+
+        // Deserialize bytes
+        ByteArrayInputStream fileInputStream = new ByteArrayInputStream(bytes);
+        ObjectInputStream objectInputStream = new ObjectInputStream(fileInputStream);
+        // Deserialized result
+        DefaultSdkAutoConstructList resultList = (DefaultSdkAutoConstructList) objectInputStream.readObject();
+        objectInputStream.close();
+
+        // Compare using "==", to make sure it is the same reference.
+        assertThat(resultList == defaultSdkAutoConstructList).isTrue();
+    }
 }

core/sdk-core/src/test/java/software/amazon/awssdk/core/util/DefaultSdkAutoConstructMapTest.java

@@ -17,7 +17,14 @@
 
 import static org.assertj.core.api.Assertions.assertThat;
 
+import java.io.ByteArrayInputStream;
+import java.io.ByteArrayOutputStream;
+import java.io.ObjectInputStream;
+import java.io.ObjectOutputStream;
 import java.util.HashMap;
+import java.util.List;
+import java.util.Map;
+import org.junit.jupiter.api.DisplayName;
 import org.junit.jupiter.api.Test;
 
 public class DefaultSdkAutoConstructMapTest {
@@ -41,4 +48,31 @@ public void hashCode_sameAsEmptyMap() {
     public void toString_emptyMap() {
         assertThat(AUTO_CONSTRUCT_MAP.toString()).isEqualTo("{}");
     }
+    @Test
+    @DisplayName("DefaultSdkAutoConstructMap is Serializable, and is same instance.")
+    public void serialization_sameSingletonInstance() throws Exception {
+        // Create instance of DefaultSdkAutoConstructMap
+        Map defaultSdkAutoConstructMap = DefaultSdkAutoConstructMap.getInstance();
+
+        // Serialize instance into byte array
+        ByteArrayOutputStream baos = new ByteArrayOutputStream();
+        ObjectOutputStream objectOutputStream = new ObjectOutputStream(baos);
+
+        objectOutputStream.writeObject(defaultSdkAutoConstructMap);
+        objectOutputStream.flush();
+        objectOutputStream.close();
+
+        // Serialization result
+        byte[] bytes = baos.toByteArray();
+
+        // Deserialize bytes
+        ByteArrayInputStream fileInputStream = new ByteArrayInputStream(bytes);
+        ObjectInputStream objectInputStream = new ObjectInputStream(fileInputStream);
+        // Deserialized result
+        DefaultSdkAutoConstructMap resultMap = (DefaultSdkAutoConstructMap) objectInputStream.readObject();
+        objectInputStream.close();
+
+        // Compare using "==", to make sure it is the same reference.
+        assertThat(resultMap == defaultSdkAutoConstructMap).isTrue();
+    }
 }