通过 Netty 中的 ServerBootstrap ChannelPipeline 发送消息时出现 UnsupportedOperationException

Question

我使用的是 Netty 5.0。

我有一个互补的客户端引导程序，我从 netty github 获取了 SecureChatClient.java 示例。 Wenn 我从客户端引导程序向服务器发送消息，它工作得很好。当我尝试从服务器引导程序向客户端发送消息时（首先通过客户端成功启动连接/通道后），我得到一个java.lang.UnsupportedOperationException，没有任何进一步的信息。从服务器向客户端发送消息是通过上面的代码完成的。

serverbootstrap 是否只用于接收？

serverbootstrap 是否不意味着能够将消息写回客户端，如上所示？我的意思是，消息可以从套接字向上通过 ChannelHandlers 进入 ChannelPipeline，但只有 ChannelHandlers 应该将响应写回 ChannelPipeline 并输出套接字。因此，在 ServerBootstrap 中，用户并不意味着能够从管道外部沿 ChannelPipeline 发送消息。 （希望这是有道理的）

或者我只是错过了什么？

我的代码如下：

    // Ports.
    int serverPort = 8080;

    EventLoopGroup bossGroup    = new NioEventLoopGroup();
    EventLoopGroup workerGroup  = new NioEventLoopGroup();
    try {
        ServerBootstrap b = new ServerBootstrap();
        b.group(bossGroup, workerGroup)
         .channel(NioServerSocketChannel.class)
         .childHandler(new ChannelInitializer<SocketChannel>() {
             @Override
             public void initChannel(SocketChannel ch) throws Exception {
                 ch.pipeline().addLast("MyMessageHandler", new MyMessageHandler());
             }
         })
         .option(ChannelOption.SO_BACKLOG, 128)
         .childOption(ChannelOption.SO_KEEPALIVE, true);

        // Bind and start to accept incoming connections.
        ChannelFuture f = b.bind(serverPort).sync();
        Channel ch = f.channel();

        System.out.println("Server: Running!");

      // Read commands from the stdin.
      ChannelFuture lastWriteFuture = null;
      BufferedReader in = new BufferedReader(new InputStreamReader(System.in));
      while(true)
      {
          String line = in.readLine();
          if (line == null) break;

          ByteBuf getOut = buffer(64);
          getOut.writeBytes(line.getBytes());

          // Sends the received line to the server.
          lastWriteFuture = ch.writeAndFlush(getOut);

          lastWriteFuture.addListener(new ChannelFutureListener() {
                @Override
                public void operationComplete(ChannelFuture cf) throws Exception {
                    if(cf.isSuccess()) {
                        System.out.println("CFListener: SUCCESS! YEAH! HELL! YEAH!");
                    } else {
                        System.out.println("CFListener: failure! FAILure! FAILURE!");
                        System.out.println(cf.cause());
                    }
                }
            });

      }

               // Wait until all messages are flushed before closing the channel.
      if (lastWriteFuture != null) {
          lastWriteFuture.sync();
      }


        // Wait until the server socket is closed.
        // In this example, this does not happen, but you can do that to gracefully
        // shut down your server.
        f.channel().closeFuture().sync();
    } catch (InterruptedException | UnsupportedOperationException e) {
        e.printStackTrace();
    } finally {
        workerGroup.shutdownGracefully();
        bossGroup.shutdownGracefully();
    }

我开始使用以下示例：https://github.com/netty/netty/tree/4.1/example/src/main/java/io/netty/example/securechat

我的问题是调用ch.writeAndFlush时出现以下异常：

java.lang.UnsupportedOperationException
at io.netty.channel.socket.nio.NioServerSocketChannel.filterOutboundMessage(NioServerSocketChannel.java:184)
at io.netty.channel.AbstractChannel$AbstractUnsafe.write(AbstractChannel.java:784)
at io.netty.channel.DefaultChannelPipeline$HeadContext.write(DefaultChannelPipeline.java:1278)
at io.netty.channel.ChannelHandlerInvokerUtil.invokeWriteNow(ChannelHandlerInvokerUtil.java:158)
at io.netty.channel.DefaultChannelHandlerInvoker$WriteTask.run(DefaultChannelHandlerInvoker.java:440)
at io.netty.util.concurrent.SingleThreadEventExecutor.runAllTasks(SingleThreadEventExecutor.java:328)
at io.netty.channel.nio.NioEventLoop.run(NioEventLoop.java:354)
at io.netty.util.concurrent.SingleThreadEventExecutor$2.run(SingleThreadEventExecutor.java:116)
at io.netty.util.internal.chmv8.ForkJoinTask$RunnableExecuteAction.exec(ForkJoinTask.java:1412)
at io.netty.util.internal.chmv8.ForkJoinTask.doExec(ForkJoinTask.java:280)
at io.netty.util.internal.chmv8.ForkJoinPool$WorkQueue.runTask(ForkJoinPool.java:877)
at io.netty.util.internal.chmv8.ForkJoinPool.scan(ForkJoinPool.java:1706)
at io.netty.util.internal.chmv8.ForkJoinPool.runWorker(ForkJoinPool.java:1661)
at io.netty.util.internal.chmv8.ForkJoinWorkerThread.run(ForkJoinWorkerThread.java:126)

Answer 1

您不能写入 ServerChannel，只能连接到普通通道。由于这个原因，您对 writeAndFlush 的呼叫失败。

要向每个客户端发送消息，您应该将每个客户端的通道存储在 ChannelGroup 中并在其上调用 writeAndFlush()。

一个快速的方法是向你的 ServerBootstrap 添加另一个处理程序，将传入的连接放入 ChannelGroup，一个快速的实现是这样的：

// In your main:
ChannelGroup allChannels =
         new DefaultChannelGroup(GlobalEventExecutor.INSTANCE);

// In your ChannelInitializer<SocketChannel>
ch.pipeline().addLast("grouper", new GlobalSendHandler());

// New class:
public class MyHandler extends ChannelInboundHandlerAdapter {
     @Override
     public void channelActive(ChannelHandlerContext ctx) {
         allChannels.add(ctx.channel());
         super.channelActive(ctx);
     }
 }

然后我们可以调用以下命令向每个连接发送消息，这将返回一个ChannelGroupFuture 而不是普通的ChannelFuture：

allChannels.writeAndFlush(getOut);

经过上述修复后，您的总代码将如下所示：

// Ports.
int serverPort = 8080;

ChannelGroup allChannels =
         new DefaultChannelGroup(GlobalEventExecutor.INSTANCE);

EventLoopGroup bossGroup    = new NioEventLoopGroup();
EventLoopGroup workerGroup  = new NioEventLoopGroup();
try {
    ServerBootstrap b = new ServerBootstrap();
    b.group(bossGroup, workerGroup)
     .channel(NioServerSocketChannel.class)
     .childHandler(new ChannelInitializer<SocketChannel>() {
         @Override
         public void initChannel(SocketChannel ch) throws Exception {
             ch.pipeline().addLast("MyMessageHandler", new MyMessageHandler());
             ch.pipeline().addLast("grouper", new GlobalSendHandler());
         }
     })
     .option(ChannelOption.SO_BACKLOG, 128)
     .childOption(ChannelOption.SO_KEEPALIVE, true);

    // Bind and start to accept incoming connections.
    ChannelFuture f = b.bind(serverPort).sync();
    Channel ch = f.channel();

    System.out.println("Server: Running!");

  // Read commands from the stdin.
  ChannelGroupFuture lastWriteFuture = null;
  BufferedReader in = new BufferedReader(new InputStreamReader(System.in));
  while(true)
  {
      String line = in.readLine();
      if (line == null) break;

      ByteBuf getOut = buffer(64);
      getOut.writeBytes(line.getBytes());

      // Sends the received line to the server.
      lastWriteFuture = allChannels.writeAndFlush(getOut);

      lastWriteFuture.addListener(new ChannelGroupFutureListener() {
            @Override
            public void operationComplete(ChannelGroupFuture cf) throws Exception {
                if(cf.isSuccess()) {
                    System.out.println("CFListener: SUCCESS! YEAH! HELL! YEAH!");
                } else {
                    System.out.println("CFListener: failure! FAILure! FAILURE!");
                    System.out.println(cf.cause());
                }
            }
        });

  }

           // Wait until all messages are flushed before closing the channel.
  if (lastWriteFuture != null) {
      lastWriteFuture.sync();
  }


    // Wait until the server socket is closed.
    // In this example, this does not happen, but you can do that to gracefully
    // shut down your server.
    f.channel().closeFuture().sync();
} catch (InterruptedException | UnsupportedOperationException e) {
    e.printStackTrace();
} finally {
    workerGroup.shutdownGracefully();
    bossGroup.shutdownGracefully();
}

Answer 2

我认为 Netty Server 没有解码器、编码器。 如果要发送字符串数据，

serverBootstrap.group(bossGroup, workerGroup).childHandler(new ChannelInitializer<SocketChannel>() {
    @Override
    protected void initChannel(SocketChannel channel) throws Exception {
        ChannelPipeline channelPipeline = channel.pipeline();
        channelPipeline.addLast("String Encoder", new StringEncoder(CharsetUtil.UTF_8));
        channelPipeline.addLast("String Decoder", new StringDecoder(CharsetUtil.UTF_8));
    }
});

添加服务器的初始化程序！