Netty如何发送对象

Question

如何使用netty发送对象。当我尝试发送一个字符串对象时，一切都很好。

channel.writeAndFlush(new String("df")); 

但是，当我试图发送一个简单的对象服务器出现错误

public class Message implements Serializable { 

    private static final long serialVersionUID = 1L; 
} 
channel.writeAndFlush(new Message()); 

---

io.netty.channel.DefaultChannelPipeline$TailHandler exceptionCaught 
WARNING: An exceptionCaught() event was fired, and it reached at the tail of the pipeline. It usually means the last handler in the pipeline did not handle the exception. 
io.netty.handler.codec.DecoderException: java.lang.NullPointerException 
    at io.netty.handler.codec.ByteToMessageDecoder.callDecode(ByteToMessageDecoder.java:259) 
    at io.netty.handler.codec.ByteToMessageDecoder.channelRead(ByteToMessageDecoder.java:141) 
    at io.netty.channel.DefaultChannelHandlerContext.invokeChannelRead(DefaultChannelHandlerContext.java:340) 
    at io.netty.channel.DefaultChannelHandlerContext.fireChannelRead(DefaultChannelHandlerContext.java:326) 
    at io.netty.channel.DefaultChannelPipeline.fireChannelRead(DefaultChannelPipeline.java:785) 
    at io.netty.channel.nio.AbstractNioByteChannel$NioByteUnsafe.read(AbstractNioByteChannel.java:116) 
    at io.netty.channel.nio.NioEventLoop.processSelectedKey(NioEventLoop.java:494) 
    at io.netty.channel.nio.NioEventLoop.processSelectedKeysOptimized(NioEventLoop.java:461) 
    at io.netty.channel.nio.NioEventLoop.processSelectedKeys(NioEventLoop.java:378) 
    at io.netty.channel.nio.NioEventLoop.run(NioEventLoop.java:350) 
    at io.netty.util.concurrent.SingleThreadEventExecutor$2.run(SingleThreadEventExecutor.java:101) 
    at java.lang.Thread.run(Thread.java:744) 
Caused by: java.lang.NullPointerException 
    at io.netty.handler.codec.serialization.CompactObjectInputStream.readClassDescriptor(CompactObjectInputStream.java:55) 
    at java.io.ObjectInputStream.readNonProxyDesc(ObjectInputStream.java:1601) 
    at java.io.ObjectInputStream.readClassDesc(ObjectInputStream.java:1517) 
    at java.io.ObjectInputStream.readOrdinaryObject(ObjectInputStream.java:1771) 
    at java.io.ObjectInputStream.readObject0(ObjectInputStream.java:1350) 
    at java.io.ObjectInputStream.readObject(ObjectInputStream.java:370) 
    at io.netty.handler.codec.serialization.ObjectDecoder.decode(ObjectDecoder.java:73) 
    at io.netty.handler.codec.LengthFieldBasedFrameDecoder.decode(LengthFieldBasedFrameDecoder.java:343) 
    at io.netty.handler.codec.ByteToMessageDecoder.callDecode(ByteToMessageDecoder.java:228) 
    ... 11 more 

---

class ChatServerInitializer extends ChannelInitializer<SocketChannel> { 

    @Override 
    protected void initChannel(SocketChannel arg0) throws Exception 
    { 
     ChannelPipeline pipeline = arg0.pipeline(); 
     pipeline.addLast("decoder", (new ObjectDecoder(null))); 
     pipeline.addLast("encoder", new ObjectEncoder()); 
     pipeline.addLast("handler", new ChatServerHandler()); 
    } 
} 

Answer 1

当你构建一个ObjectDecoder您指定null而这导致NullPointerException这里。相反，你必须指定类似ClassResolvers.weakCachingResolver(MyMessage.class.getClassLoader())。

Answer 2

这是不对的：

new ObjectDecoder(null) 

尝试做这样的：

serverBootstrap.childHandler(new ChannelInitializer<SocketChannel>() { 
     @Override 
     protected void initChannel(SocketChannel socketChannel) throws Exception { 
      socketChannel.pipeline().addLast(
        new ObjectDecoder(ClassResolvers.softCachingResolver(ClassLoader.getSystemClassLoader())), 
        new ObjectEncoder(), 
        new Handler()); 
     } 
    });