Odtnhj

I try to send object message PingMessage with netty. Add ObjectEncoder and ObjectDecoder in channel pipeline. Client has sent packet successfully, but server can't decode the message. ObjectDecoder#decode() just returns null. Netty version is 4.1.28.Final.

PingMessage

public class PingMessage implements Serializable 
 private static final long serialVersionUID = 1L;
 private int flag = 0xff3e;
 private String ping = "ping";

 public int getFlag() 
 return flag;
 

 public void setFlag(int flag) 
 this.flag = flag;
 

 public String getPing() 
 return ping;
 

 public void setPing(String ping) 
 this.ping = ping;
 

client

public class HeartbeatInitializer extends ChannelInitializer<Channel> 

 protected void initChannel(Channel ch) throws Exception 
 ChannelPipeline pipeline = ch.pipeline();
 pipeline.addLast(new ObjectEncoder());
 pipeline.addLast(new ObjectDecoder(Integer.MAX_VALUE, ClassResolvers.weakCachingResolver(PongMessage.class.getClassLoader())));
 pipeline.addLast(new IdleStateHandler(BusinessConstant.READER_IDLE_SECONDS, BusinessConstant.WRITER_IDLE_SECONDS, 0));
 pipeline.addLast(new HeartbeatServerHandler());
 pipeline.addLast(new ClientHandler());
 


public class HeartbeatServerHandler extends ChannelDuplexHandler 
 private static Logger logger = LoggerFactory.getLogger(HeartbeatServerHandler.class);

 @Override
 public void userEventTriggered(ChannelHandlerContext ctx, Object evt) throws Exception 
 if (evt instanceof IdleStateEvent) 
 IdleStateEvent idleState = (IdleStateEvent)evt;
 if (idleState.state() == IdleState.READER_IDLE) 
 else if (idleState.state() == IdleState.WRITER_IDLE) 
 try 
 ChannelFuture future = ctx.writeAndFlush(new PingMessage()).sync(); 
 catch (Exception e) 
 e.printStackTrace();
 
 
 
 

server

public class HeartbeatInitializer extends ChannelInitializer<Channel> 

 protected void initChannel(Channel ch) throws Exception 
 ChannelPipeline pipeline = ch.pipeline();
 pipeline.addLast(new ObjectEncoder());
 pipeline.addLast(new ObjectDecoder(Integer.MAX_VALUE, ClassResolvers.weakCachingResolver(this.class.getClassLoader())));
 pipeline.addLast(new IdleStateHandler(BusinessConstant.READER_IDLE_SECONDS, BusinessConstant.WRITER_IDLE_SECONDS, 0));
 pipeline.addLast(new HeartbeatServerHandler());
 pipeline.addLast(new ClientHandler());
 


public class HeartbeatServerHandler extends ChannelDuplexHandler 
 private static Logger logger = LoggerFactory.getLogger(HeartbeatServerHandler.class);

 @Override
 public void channelRead(ChannelHandlerContext ctx, Object msg) 
 if (msg instanceof PingMessage) 
 logger.info("received ping");
 return;
 
 

netty source code debug info

AbstractChannelHandlerContext#invokeChannelRead()

((ChannelInboundHandler) handler()).channelRead(this, msg);

the msg variable is

UnpooledUnsafeDirectByteBuf(ridx: 0, widx: 61, cap: 1024)

ObjectDecoder#decode() just return null

super class of ObjectDecoder is LengthFieldBasedFrameDecoder. LengthFieldBasedFrameDecoder#decode() return null

// LengthFieldBasedFrameDecoder#decode()

int frameLengthInt = (int) frameLength;
if (in.readableBytes() < frameLengthInt) 
 return null; // get executed and return null