[#1560] Feature/intermediate representation data format

messaging/src/main/java/org/axonframework/serialization/upcasting/event/InitialEventRepresentation.java

@@ -148,4 +148,14 @@ public Instant getTimestamp() {
     public LazyDeserializingObject<MetaData> getMetaData() {
         return metaData;
     }
+
+    @Override
+    public <D> Boolean canConvertDataTo(Class<D> requiredType) {
+        return serializer.getConverter().canConvert(data.getContentType(), requiredType);
+    }
+
+    @Override
+    public Serializer getSerializer() {
+        return serializer;
+    }
 }

messaging/src/main/java/org/axonframework/serialization/upcasting/event/IntermediateEventRepresentation.java

@@ -21,6 +21,7 @@
 import org.axonframework.serialization.LazyDeserializingObject;
 import org.axonframework.serialization.SerializedObject;
 import org.axonframework.serialization.SerializedType;
+import org.axonframework.serialization.Serializer;
 
 import java.time.Instant;
 import java.util.Optional;
@@ -139,4 +140,18 @@ <T> IntermediateEventRepresentation upcast(SerializedType outputType, Class<T> e
      * @return the MetaData of the message wrapping the object to upcast, if available
      */
     LazyDeserializingObject<MetaData> getMetaData();
+
+    /**
+     * Checks if the data can be converted to required type.
+     *
+     * @param requiredType the type to convert to
+     * @return true, if the intermediate representation can be converted to desired type.
+     */
+    <D> Boolean canConvertDataTo(Class<D> requiredType);
+
+    /**
+     * Retrieves the serializer used to retrieve data.
+     * @return serializer configured for event serialization.
+     */
+    Serializer getSerializer();
 }

messaging/src/main/java/org/axonframework/serialization/upcasting/event/UpcastedEventRepresentation.java

@@ -22,6 +22,7 @@
 import org.axonframework.serialization.LazyDeserializingObject;
 import org.axonframework.serialization.SerializedObject;
 import org.axonframework.serialization.SerializedType;
+import org.axonframework.serialization.Serializer;
 import org.axonframework.serialization.SimpleSerializedObject;
 
 import java.time.Instant;
@@ -136,4 +137,15 @@ public LazyDeserializingObject<MetaData> getMetaData() {
         }
         return metaData;
     }
+
+    @Override
+    public <D> Boolean canConvertDataTo(Class<D> requiredType) {
+        return converter.canConvert(source.getData().getContentType(), requiredType);
+    }
+
+    @Override
+    public Serializer getSerializer() {
+        // upcasted representation has no serializer, ask the previous representation, until the InitialEventRepresentation answers the question.
+        return source.getSerializer();
+    }
 }

messaging/src/test/java/org/axonframework/serialization/upcasting/event/IntermediateRepresentationTest.java

@@ -0,0 +1,105 @@
+/*
+ * Copyright (c) 2010-2020. Axon Framework
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *    http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.axonframework.serialization.upcasting.event;
+
+import org.axonframework.eventhandling.EventData;
+import org.axonframework.eventhandling.GenericDomainEventMessage;
+import org.axonframework.serialization.Converter;
+import org.axonframework.serialization.Serializer;
+import org.axonframework.serialization.xml.XStreamSerializer;
+import org.axonframework.utils.TestDomainEventEntry;
+import org.junit.jupiter.api.Test;
+
+import java.util.List;
+import java.util.function.Function;
+import java.util.stream.Stream;
+
+import static java.util.stream.Collectors.toList;
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.mockito.Mockito.*;
+
+/**
+ * Test for intermediate representation.
+ *
+ * @author Simon Zambrovski
+ */
+public class IntermediateRepresentationTest {
+
+    private final static Serializer serializer = XStreamSerializer.defaultSerializer();
+
+    @Test
+    public void should_deliver_serializer() {
+        EventData<?> eventData = new TestDomainEventEntry(
+            new GenericDomainEventMessage<>("test", "aggregateId", 0, "someString"), serializer
+        );
+        IntermediateEventRepresentation input = new InitialEventRepresentation(eventData, serializer);
+        EventUpcasterChain eventUpcasterChain = new EventUpcasterChain(
+            new IntermediateRepresentationTest.MyEventUpcaster(),
+            new IntermediateRepresentationTest.MyEventUpcaster(),
+            new IntermediateRepresentationTest.MyEventUpcaster()
+        );
+        List<IntermediateEventRepresentation> result = eventUpcasterChain.upcast(Stream.of(input)).collect(toList());
+        assertEquals(1, result.size());
+        IntermediateEventRepresentation output = result.get(0);
+        assertEquals(serializer, output.getSerializer());
+    }
+
+
+    @Test
+    public void can_convert_data_to() {
+        EventData<?> eventData = new TestDomainEventEntry(
+            new GenericDomainEventMessage<>("test", "aggregateId", 0, "someString"), serializer
+        );
+        Serializer serializer = mock(Serializer.class);
+        Converter converter = mock(Converter.class);
+        when(serializer.getConverter()).thenReturn(converter);
+        when(converter.canConvert(any(), eq(String.class))).thenReturn(true);
+
+        IntermediateEventRepresentation input = new InitialEventRepresentation(eventData, serializer);
+        EventUpcasterChain eventUpcasterChain = new EventUpcasterChain(
+            new IntermediateRepresentationTest.MyEventUpcaster()
+        );
+        List<IntermediateEventRepresentation> result = eventUpcasterChain.upcast(Stream.of(input)).collect(toList());
+        assertEquals(1, result.size());
+
+
+        assertEquals(true, input.canConvertDataTo(String.class));
+        assertEquals(true, result.get(0).canConvertDataTo(String.class));
+
+        verify(converter, atMostOnce()).canConvert(String.class, String.class);
+    }
+
+    private static class MyEventUpcaster extends SingleEventUpcaster {
+
+        @Override
+        protected boolean canUpcast(IntermediateEventRepresentation intermediateRepresentation) {
+            return true;
+        }
+
+        @Override
+        protected IntermediateEventRepresentation doUpcast(IntermediateEventRepresentation intermediateRepresentation) {
+            return new UpcastedEventRepresentation<>(
+                intermediateRepresentation.getType(),
+                intermediateRepresentation,
+                Function.identity(),
+                Function.identity(),
+                Object.class,
+                serializer.getConverter()
+            );
+        }
+    }
+}