protobuf-json序列化方式bug

[CodingSinger]

• I have searched the issues of this repository and believe that this is not a duplicate.
• I have checked the FAQ of this repository and believe that this is not a duplicate.

Environment

• Dubbo version: 2.7.2
• Operating System version: macOS 10.12.6
• Java version: 1.8

Steps to reproduce this issue

1. 使用protobuf-json的序列化方式
2. 进行普通的dubbo RPC调用

Expected Result

正常调用

Actual Result

报错,序列化失败

If there is an exception, please attach the exception trace:

Caused by: java.lang.IllegalArgumentException: This serialization only support google protobuf object, the object class is: java.lang.String
	at org.apache.dubbo.common.serialize.protobuf.support.GenericProtobufObjectOutput.writeObject(GenericProtobufObjectOutput.java:94)
	at org.apache.dubbo.common.serialize.protobuf.support.GenericProtobufObjectOutput.writeUTF(GenericProtobufObjectOutput.java:74)
	at org.apache.dubbo.rpc.protocol.dubbo.DubboCodec.encodeRequestData(DubboCodec.java:176)
	at org.apache.dubbo.remoting.exchange.codec.ExchangeCodec.encodeRequest(ExchangeCodec.java:238)
	at org.apache.dubbo.remoting.exchange.codec.ExchangeCodec.encode(ExchangeCodec.java:69)
	at org.apache.dubbo.rpc.protocol.dubbo.DubboCountCodec.encode(DubboCountCodec.java:40)
	at org.apache.dubbo.remoting.transport.netty4.NettyCodecAdapter$InternalEncoder.encode(NettyCodecAdapter.java:70)
	at io.netty.handler.codec.MessageToByteEncoder.write(MessageToByteEncoder.java:107)
	... 23 more

	at org.apache.dubbo.remoting.exchange.support.DefaultFuture.doReceived(DefaultFuture.java:191)
	at org.apache.dubbo.remoting.exchange.support.DefaultFuture.received(DefaultFuture.java:153)
	at org.apache.dubbo.remoting.exchange.support.DefaultFuture.received(DefaultFuture.java:141)
	at org.apache.dubbo.remoting.exchange.support.header.HeaderExchangeHandler.handleResponse(HeaderExchangeHandler.java:62)
	at org.apache.dubbo.remoting.exchange.support.header.HeaderExchangeHandler.received(HeaderExchangeHandler.java:199)
	at org.apache.dubbo.remoting.transport.DecodeHandler.received(DecodeHandler.java:51)
	at org.apache.dubbo.remoting.transport.dispatcher.ChannelEventRunnable.run(ChannelEventRunnable.java:57)
	... 3 more

[CodingSinger]

完整异常栈

org.apache.dubbo.rpc.RpcException: Failed to invoke remote method: createUser, provider: dubbo://localhost:8080/org.apache.dubbo.benchmark.service.UserServicePb?application=dubbo-protostuff-client&check=false&client=netty4&dubbo=2.0.2&interface=org.apache.dubbo.benchmark.service.UserServicePb&lazy=false&methods=existUser,getUser,createUser,listUser&pid=16632&reference.filter=-default&register.ip=10.4.144.235&remote.application=&revision=1.0-SNAPSHOT&serialization=protobuf-json&side=consumer&sticky=false&timestamp=1563791866651, cause: org.apache.dubbo.remoting.RemotingException: io.netty.handler.codec.EncoderException: java.lang.IllegalArgumentException: This serialization only support google protobuf object, the object class is: java.lang.String
io.netty.handler.codec.EncoderException: java.lang.IllegalArgumentException: This serialization only support google protobuf object, the object class is: java.lang.String
	at io.netty.handler.codec.MessageToByteEncoder.write(MessageToByteEncoder.java:125)
	at io.netty.channel.AbstractChannelHandlerContext.invokeWrite0(AbstractChannelHandlerContext.java:738)
	at io.netty.channel.AbstractChannelHandlerContext.invokeWrite(AbstractChannelHandlerContext.java:730)
	at io.netty.channel.AbstractChannelHandlerContext.write(AbstractChannelHandlerContext.java:816)
	at io.netty.channel.AbstractChannelHandlerContext.write(AbstractChannelHandlerContext.java:723)
	at io.netty.handler.timeout.IdleStateHandler.write(IdleStateHandler.java:304)
	at io.netty.channel.AbstractChannelHandlerContext.invokeWrite0(AbstractChannelHandlerContext.java:738)
	at io.netty.channel.AbstractChannelHandlerContext.invokeWrite(AbstractChannelHandlerContext.java:730)
	at io.netty.channel.AbstractChannelHandlerContext.write(AbstractChannelHandlerContext.java:816)
	at io.netty.channel.AbstractChannelHandlerContext.write(AbstractChannelHandlerContext.java:723)
	at io.netty.channel.ChannelDuplexHandler.write(ChannelDuplexHandler.java:106)
	at org.apache.dubbo.remoting.transport.netty4.NettyClientHandler.write(NettyClientHandler.java:87)
	at io.netty.channel.AbstractChannelHandlerContext.invokeWrite0(AbstractChannelHandlerContext.java:738)
	at io.netty.channel.AbstractChannelHandlerContext.invokeWrite(AbstractChannelHandlerContext.java:730)
	at io.netty.channel.AbstractChannelHandlerContext.access$1900(AbstractChannelHandlerContext.java:38)
	at io.netty.channel.AbstractChannelHandlerContext$AbstractWriteTask.write(AbstractChannelHandlerContext.java:1081)
	at io.netty.channel.AbstractChannelHandlerContext$WriteAndFlushTask.write(AbstractChannelHandlerContext.java:1128)
	at io.netty.channel.AbstractChannelHandlerContext$AbstractWriteTask.run(AbstractChannelHandlerContext.java:1070)
	at io.netty.util.concurrent.AbstractEventExecutor.safeExecute(AbstractEventExecutor.java:163)
	at io.netty.util.concurrent.SingleThreadEventExecutor.runAllTasks(SingleThreadEventExecutor.java:404)
	at io.netty.channel.nio.NioEventLoop.run(NioEventLoop.java:465)
	at io.netty.util.concurrent.SingleThreadEventExecutor$5.run(SingleThreadEventExecutor.java:884)
	at io.netty.util.concurrent.FastThreadLocalRunnable.run(FastThreadLocalRunnable.java:30)
	at java.lang.Thread.run(Thread.java:748)
Caused by: java.lang.IllegalArgumentException: This serialization only support google protobuf object, the object class is: java.lang.String
	at org.apache.dubbo.common.serialize.protobuf.support.GenericProtobufObjectOutput.writeObject(GenericProtobufObjectOutput.java:94)
	at org.apache.dubbo.common.serialize.protobuf.support.GenericProtobufObjectOutput.writeUTF(GenericProtobufObjectOutput.java:74)
	at org.apache.dubbo.rpc.protocol.dubbo.DubboCodec.encodeRequestData(DubboCodec.java:176)
	at org.apache.dubbo.remoting.exchange.codec.ExchangeCodec.encodeRequest(ExchangeCodec.java:238)
	at org.apache.dubbo.remoting.exchange.codec.ExchangeCodec.encode(ExchangeCodec.java:69)
	at org.apache.dubbo.rpc.protocol.dubbo.DubboCountCodec.encode(DubboCountCodec.java:40)
	at org.apache.dubbo.remoting.transport.netty4.NettyCodecAdapter$InternalEncoder.encode(NettyCodecAdapter.java:70)
	at io.netty.handler.codec.MessageToByteEncoder.write(MessageToByteEncoder.java:107)
	... 23 more

	at org.apache.dubbo.rpc.protocol.AsyncToSyncInvoker.invoke(AsyncToSyncInvoker.java:63)
	at org.apache.dubbo.rpc.protocol.ProtocolFilterWrapper$CallbackRegistrationInvoker.invoke(ProtocolFilterWrapper.java:150)
	at org.apache.dubbo.rpc.listener.ListenerInvokerWrapper.invoke(ListenerInvokerWrapper.java:78)
	at org.apache.dubbo.rpc.proxy.InvokerInvocationHandler.invoke(InvokerInvocationHandler.java:55)
	at org.apache.dubbo.common.bytecode.proxy0.createUser(proxy0.java)
	at org.apache.dubbo.benchmark.ClientPb.createUser(ClientPb.java:82)
	at org.apache.dubbo.benchmark.generated.ClientPb_createUser_jmhTest.createUser_Throughput(ClientPb_createUser_jmhTest.java:78)
	at sun.reflect.GeneratedMethodAccessor4.invoke(Unknown Source)
	at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
	at java.lang.reflect.Method.invoke(Method.java:498)
	at org.openjdk.jmh.runner.BenchmarkHandler$BenchmarkTask.call(BenchmarkHandler.java:453)
	at org.openjdk.jmh.runner.BenchmarkHandler$BenchmarkTask.call(BenchmarkHandler.java:437)
	at java.util.concurrent.FutureTask.run(FutureTask.java:266)
	at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:511)
	at java.util.concurrent.FutureTask.run(FutureTask.java:266)
	at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149)
	at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
	at java.lang.Thread.run(Thread.java:748)