upgrade protobuf version to support proto3

pom.xml

@@ -188,7 +188,7 @@
 		<dependency>
 			<groupId>com.google.protobuf</groupId>
 			<artifactId>protobuf-java</artifactId>
-			<version>2.6.1</version>
+			<version>3.6.1</version>
 			<optional>true</optional>
 		</dependency>
 		<dependency>

src/main/java/de/javakaffee/kryoserializers/protobuf/ProtobufSerializer.java

@@ -4,13 +4,14 @@
 import com.esotericsoftware.kryo.Serializer;
 import com.esotericsoftware.kryo.io.Input;
 import com.esotericsoftware.kryo.io.Output;
+import com.google.protobuf.AbstractMessage;
 import com.google.protobuf.GeneratedMessage;
 
 import java.lang.reflect.InvocationTargetException;
 import java.lang.reflect.Method;
 import static com.esotericsoftware.kryo.Kryo.NULL;
 
-public class ProtobufSerializer<T extends GeneratedMessage> extends Serializer<T> {
+public class ProtobufSerializer<T extends AbstractMessage> extends Serializer<T> {
 
     private Method parseFromMethod = null;
 

src/test/java/de/javakaffee/kryoserializers/protobuf/ProtobufSerializerTest.java

@@ -20,8 +20,8 @@ public class ProtobufSerializerTest {
     @BeforeTest
     public void setUp() throws Exception {
         _kryo = new Kryo();
-        _kryo.register(SampleProtoA.class, new ProtobufSerializer());
-        _kryo.register(SampleProtoB.class, new ProtobufSerializer());
+        _kryo.register(SampleProtoA.class, new ProtobufSerializer<SampleProtoA>());
+        _kryo.register(SampleProtoB.class, new ProtobufSerializer<SampleProtoB>());
     }
 
     @Test

src/test/resources/SampleProtoA.proto

@@ -1,9 +1,10 @@
+syntax = "proto3";
 package ProtocolBuffers; // the namespace for the compiled classes
 
 option java_package = "de.javakaffee.kryoserializers.protobuf";
 option java_outer_classname = "SampleProtoAOuterClass";
 
 message SampleProtoA {
-    optional string name = 1;
-    optional uint32 message_id = 2;
+    string name = 1;
+    uint32 message_id = 2;
 }

src/test/resources/SampleProtoB.proto

@@ -1,10 +1,11 @@
+syntax = "proto3";
 package ProtocolBuffers; // the namespace for the compiled classes
 
 option java_package = "de.javakaffee.kryoserializers.protobuf";
 option java_outer_classname = "SampleProtoBOuterClass";
 
 message SampleProtoB {
-    required uint32 identifier = 1;
-    required string state = 2;
-    required string city = 3;
+    uint32 identifier = 1;
+    string state = 2;
+    string city = 3;
 }