Implement comparable on EventData (Azure#395)

azure-eventhubs/src/main/java/com/microsoft/azure/eventhubs/EventData.java

@@ -30,7 +30,7 @@
  * Section (iii) is used for advanced scenarios, where the sending application uses third-party AMQP library to send the message to EventHubs and the receiving application
  * uses this client library to receive {@link EventData}.
  */
-public interface EventData extends Serializable {
+public interface EventData extends Serializable, Comparable<EventData> {
 
     /**
      * Construct EventData to Send to EventHubs.

azure-eventhubs/src/main/java/com/microsoft/azure/eventhubs/impl/EventDataImpl.java

@@ -258,4 +258,12 @@ private void readObject(ObjectInputStream in) throws IOException, ClassNotFoundE
             this.bodyData = new Binary(data, 0, length);
         }
     }
+
+    @Override
+    public int compareTo(EventData other) {
+        return Long.compare(
+                this.getSystemProperties().getSequenceNumber(),
+                other.getSystemProperties().getSequenceNumber()
+        );
+    }
 }

azure-eventhubs/src/test/java/com/microsoft/azure/eventhubs/eventdata/InteropEventBodyTest.java

@@ -37,7 +37,6 @@ public class InteropEventBodyTest extends ApiTestBase {
     static PartitionSender partitionSender;
     static EventData receivedEvent;
     static EventData reSentAndReceivedEvent;
-    static Message reSendAndReceivedMessage;
 
     @BeforeClass
     public static void initialize() throws EventHubException, IOException, InterruptedException, ExecutionException {

azure-eventhubs/src/test/java/com/microsoft/azure/eventhubs/impl/EventDataOrderTest.java

@@ -0,0 +1,52 @@
+/*
+ * Copyright (c) Microsoft. All rights reserved.
+ * Licensed under the MIT license. See LICENSE file in the project root for full license information.
+ */
+package com.microsoft.azure.eventhubs.impl;
+
+import java.util.ArrayList;
+import java.util.Collections;
+import java.util.HashMap;
+
+import com.microsoft.azure.eventhubs.EventData;
+import org.apache.qpid.proton.amqp.Symbol;
+import org.apache.qpid.proton.amqp.messaging.MessageAnnotations;
+import org.apache.qpid.proton.message.Message;
+import org.junit.Assert;
+import org.junit.Test;
+
+public class EventDataOrderTest {
+
+  private EventData constructMessage(long seqNumber) {
+    HashMap<Symbol, Object> properties = new HashMap<>();
+    properties.put(AmqpConstants.SEQUENCE_NUMBER, seqNumber);
+
+    Message message = Message.Factory.create();
+
+    message.setMessageAnnotations(new MessageAnnotations(properties));
+
+    return new EventDataImpl(message);
+  }
+
+  @Test
+  public void eventDataEmptyByteArray() {
+    ArrayList<EventData> messages = new ArrayList<>();
+
+    EventData first = constructMessage(19);
+    EventData second = constructMessage(22);
+    EventData third = constructMessage(25);
+    EventData last = constructMessage(88);
+
+    messages.add(second);
+    messages.add(first);
+    messages.add(last);
+    messages.add(third);
+
+    Collections.sort(messages);
+
+    Assert.assertEquals(messages.get(0), first);
+    Assert.assertEquals(messages.get(1), second);
+    Assert.assertEquals(messages.get(2), third);
+    Assert.assertEquals(messages.get(3), last);
+  }
+}