2

我正在尝试使用 ChannelContext.attr() 方法将对象从一个处理程序传递到另一个处理程序：

private class TCPInitializer extends ChannelInitializer<SocketChannel>
{
    @Override
    public void initChannel(final SocketChannel ch) throws Exception
    {
        ChannelPipeline pipeline = ch.pipeline();

        pipeline.addLast(new ReadTimeoutHandler(mIdleTimeout));
        pipeline.addLast(new HostMappingHandler<SyslogHandler>(mRegisteredClients,
                                                               mChannels));
        pipeline.addLast(new DelimiterBasedFrameDecoder(MAX_FRAME_SIZE,
                         Delimiters.lineDelimiter()));
        pipeline.addLast(new Dispatcher());
    }
}

HostMappingHandler 是一个将主机映射到数据的模板类：

public class HostMappingHandler<T> extends ChannelStateHandlerAdapter
{

    public static final AttributeKey<HostMappedObject> HOST_MAPPING =
        new AttributeKey<HostMappedObject>("HostMappingHandler.attr");


    private final ChannelGroup mChannels;
    private final Map<String, T> mMap;


    public HostMappingHandler(Map<String, T> registrations,
                              ChannelGroup channelGroup)
    {
        mChannels = channelGroup;
        mMap = registrations;
    }

    @Override
    public void channelRegistered(ChannelHandlerContext ctx) throws Exception
    {
        SocketAddress addr = ctx.channel().remoteAddress();
        T mappedObj = null;

        if (addr instanceof InetSocketAddress)
        {
            String host = ((InetSocketAddress) addr).getHostName().toLowerCase();
            mappedObj = mMap.get(host);
        }

        if (mappedObj != null)
        {
            // Add the channel to the list so it can be easily removed if unregistered
            mChannels.add(ctx.channel());

            // Attach the host-mapped object
            ctx.attr(HOST_MAPPING).set(new HostMappedObject<T>(mappedObj));
        }
        else
        {
            log.debug("Bad host [" + addr + "]; aborting connection request");
            ctx.channel().close();
        }
        super.channelRegistered(ctx);
    }

    @Override
    public void inboundBufferUpdated(ChannelHandlerContext ctx) throws Exception
    {
        // Find the parser for this host. If the host is no longer registered,
        // disconnect the client.
        if (ctx.channel().remoteAddress() instanceof InetSocketAddress)
        {
            InetSocketAddress addr = (InetSocketAddress) ctx.channel().remoteAddress();
            T handler = mMap.get(addr.getHostName().toLowerCase());

            if (handler == null)
            {
                log.debug("Host no longer registered");
                ctx.channel().close();
            }
            else
            {
                log.debug("Sanity Check: " + ctx.attr(HostMappingHandler.HOST_MAPPING).get());
            }
        }
        super.inboundBufferUpdated(ctx);
    }

    // ==================================================

    public static class HostMappedObject<C>
    {
        private final C mObj;

        public HostMappedObject(final C in)
        {
            mObj = in;
        }

        public C get()
        {
            return mObj;
        }
    }
}

而调度器目前非常简单：

private static class Dispatcher extends ChannelInboundMessageHandlerAdapter<Object>
{
    @Override
    public void messageReceived(final ChannelHandlerContext ctx,
                                final Object msg)
            throws Exception
    {
        HostMappingHandler.HostMappedObject wrapper =
                ctx.attr(HostMappingHandler.HOST_MAPPING).get();

        log.debug("Received: " + wrapper);
    }
}

顺便说一句，初始化程序和调度程序是“服务器”对象的私有类。但是，当我运行一个注册 localhost 并尝试连接它的单元测试时，它会失败并且我的调试输出显示：

HostMappingHandler.inboundBufferUpdated: Sanity Check: test.comms.netty.HostMappingHandler$HostMappedObject@eb017e
Dispatcher.messageReceived: Received: null

因此，在通道注册和接收 HostMapper 类中的入站消息之间肯定会保留映射，并且在调试器中进一步调查表明 Dispatcher 中上下文的属性映射确实有一个条目 - 问题是该值为 NULL而不是对象。

我是否遗漏了一些明显的东西，或者只是一个 alpha 错误？

编辑：

我现在已经通过将数据附加到 Dispatcher 的上下文来解决这个问题，让 HostMappingHandler 也接受一个要附加的类。该错误似乎是在处理程序的 ChannelHandlerContext 中设置属性会导致该属性出现在另一个具有正确键但值为 NULL 的处理程序中。在不知道所需工作流的情况下，错误是根本不应该出现键，或者值不应该为空。

public HostMappingHandler(final Map<String, T> registrations,
                          final ChannelGroup channelGroup,
                          final Class<? extends ChannelHandler> channelHandler)
{
    mChannels = channelGroup;
    mMap = registrations;
    mHandler = channelHandler;
}

//...

@Override
public void channelRegistered(ChannelHandlerContext ctx) throws Exception
{
    //...
    // Attach the host-mapped object
     ctx.pipeline().context(mHandler).attr(HOST_MAPPING).set(new HostMappedObject<T>(mappedObj));
    //...
}
4

1 回答 1

10

AttributeMapinChannelHandlerContext绑定到上下文，这就是为什么您在一个上下文中设置的属性在其他上下文中不可见的原因。

请注意，它Channel也实现了AttributeMap. 您可以只使用绑定到通道的属性映射：

ctx.channel().attr(...) ...;
于 2012-08-23T10:52:38.613 回答