netty 中的解码器、编码器、ServerHandler 管道

Question

查看文档，它是这样说的：

https://netty.io/4.0/api/io/netty/channel/ChannelPipeline.html

A user is supposed to have one or more ChannelHandlers in a pipeline to receive I/O events (e.g. read) and to request I/O operations (e.g. write and close). For example, a typical server will have the following handlers in each channel's pipeline, but your mileage may vary depending on the complexity and characteristics of the protocol and business logic:

Protocol Decoder - translates binary data (e.g. ByteBuf) into a Java object. Protocol Encoder - translates a Java object into binary data.

Business Logic Handler - performs the actual business logic (e.g. database access). and it could be represented as shown in the following example: static final EventExecutorGroup group = new DefaultEventExecutorGroup(16); ...

ChannelPipeline pipeline = ch.pipeline();

pipeline.addLast("decoder", new MyProtocolDecoder());

pipeline.addLast("encoder", new MyProtocolEncoder());

// Tell the pipeline to run MyBusinessLogicHandler's event handler methods // in a different thread than an I/O thread so that the I/O thread is not blocked by // a time-consuming task. // If your business logic is fully asynchronous or finished very quickly, you don't // need to specify a group.

pipeline.addLast(group, "handler", new MyBusinessLogicHandler());

在 Github 上的许多示例中，我看到了相同的模式。我想知道是否有人可以解释为什么 businessHandler 不在解码器和编码器之间。我认为您会得到您的 POJO，然后在业务处理程序中对其进行处理，然后对其进行编码。

Answer 1

当然，业务处理程序在解码器和 encoder.Take Factorial 示例的示例之间。

   public void initChannel(SocketChannel ch) {
    ChannelPipeline pipeline = ch.pipeline();
    if (sslCtx != null) {
        pipeline.addLast(sslCtx.newHandler(ch.alloc()));
    }
    // Enable stream compression (you can remove these two if unnecessary)
    pipeline.addLast(ZlibCodecFactory.newZlibEncoder(ZlibWrapper.GZIP));
    pipeline.addLast(ZlibCodecFactory.newZlibDecoder(ZlibWrapper.GZIP));
    // Add the number codec first,
    pipeline.addLast(new BigIntegerDecoder());
    pipeline.addLast(new NumberEncoder());
    // and then business logic.
    // Please note we create a handler for every new channel
    // because it has stateful properties.
    pipeline.addLast(new FactorialServerHandler());
}`

在initChannelpipeline的函数中想到先添加encoder和decoder，最后添加handler。执行流程实际上按解码器、处理程序和编码器排序。 decoder,handler 和 encoder 等处理程序实际上存储在 AbstractChannelHandlerContextclass 中。 Netty中有一个AbstractChannelHandlerContext的链表。列表排列成decoder context-->handler context-->encoder context，执行也是一样！

Answer 2

由于调用处理程序的顺序，解码器和编码器通常位于管道的开头。对于传入数据，它是自下而上的，而对于传出数据，它是自上而下的。

例如

pipeline.addLast(new MyEncoder());
pipeline.addLast(new MyDecoder());
pipeline.addLast(new MyBusiness());

在这种情况下，对于传入数据调用顺序是：MyDecoder（将数据转换为 POJO）-> MyBusiness（传入流不调用编码器）和传出数据：MyBusiness->MyEncoder（解码器不是要求传出流）。

如果您在业务处理程序（实际上是解码器之后的 POJO）中接收到一个传入流，对其进行处理并将其写回，看起来 MyBusiness 位于编码器和解码器之间，因为数据正在返回到编码器。

Answer 3

事实上，如果你在你的服务器中添加1.decoder，2.businessHandler，3.encoder，然后写成ctx.channel().writeAndFlush()或者ctx.pipeline().writeAndFlush()，encoder就会被调用。在这种情况下是 bc，它将从尾部开始寻找上一个 outboundChannel。但是，如果您写 ctx.writeAndFlush()，它会从 businessHandler 的位置寻找上一个 outboundChannel。在AbstractChannelHandlerContext的findContextOutbound()第一行加个断点，就搞定了

private AbstractChannelHandlerContext findContextOutbound(int mask) {
        AbstractChannelHandlerContext ctx = this;
        EventExecutor currentExecutor = executor();
        do {
            ctx = ctx.prev;
        } while (skipContext(ctx, currentExecutor, mask, MASK_ONLY_OUTBOUND));
        return ctx;
    }

netty 中的解码器、编码器、ServerHandler 管道

Decoder, Encoder, ServerHandler pipeline in netty

java

netty