入站处理 ChannelInboundHandler
出站处理 ChannelOutboundHandler

ChannelInboundHandler
ChannelInboundHandlerAdapter
SimpleChannelInboundHandler

void channelRead(ChannelHandlerContext ctx, Object msg) throws Exception;
void userEventTriggered(ChannelHandlerContext ctx, Object evt) throws Exception;
channelRead 处理 msg

一般使用 ChannelInboundHandlerAdapter

public class ChannelInboundHandlerAdapter extends ChannelHandlerAdapter implements ChannelInboundHandler {


public class HelloInHandler extends ChannelInboundHandlerAdapter {
	@Override
	public void channelRead(ChannelHandlerContext ctx, Object msg) throws Exception {
		if(msg instanceof ByteBuf){		
			ByteBuf in = (ByteBuf)msg;
			try {
				if(in.readableBytes() > 0){
					String str = in.toString(CharsetUtil.UTF_8);
					System.out.println("receive msg:" + str);
				}
            } finally {
            	// 释放资源 !!! 
                ReferenceCountUtil.release(in);
            }
		}
	}
}

继承 ChannelInboundHandlerAdapter  注释资源释放 
ReferenceCountUtil.release

SimpleChannelInboundHandler 把资源释放逻辑模板化


public abstract class SimpleChannelInboundHandler< I > extends ChannelInboundHandlerAdapter {
    @Override
    public void channelRead(ChannelHandlerContext ctx, Object msg) throws Exception {
        boolean release = true;
        try {
            if (acceptInboundMessage(msg)) {
                @SuppressWarnings("unchecked")
                I imsg = (I) msg;
                channelRead0(ctx, imsg);
            } else {
                release = false;
                ctx.fireChannelRead(msg);
            }
        } finally {
            if (autoRelease && release) {
                ReferenceCountUtil.release(msg);
            }
        }
    }
    
    // 需要我们主动实现的接口
    protected abstract void channelRead0(ChannelHandlerContext ctx, I msg) throws Exception;
    ...
}


public class HelloSimpleInHandler extends SimpleChannelInboundHandler< ByteBuf > {
	@Override
	protected void channelRead0(ChannelHandlerContext ctx, ByteBuf msg) throws Exception {
		if(msg.readableBytes() > 0){
			String str = msg.toString(CharsetUtil.UTF_8);
			System.out.println("receive msg: " + str);
		}
	}
}

继承 SimpleChannelInboundHandler ，实现 channelRead0  不需要释放资源




StringDecoder  +  HelloHandler

public class HelloHandler extends SimpleChannelInboundHandler< String > {
	@Override
	protected void channelRead0(ChannelHandlerContext ctx, String msg) throws Exception {
		System.out.println("receive msg: " + msg);
	}
}


bootstrap.childHandler(new ChannelInitializer< Channel>() {
 
    @Override
    protected void initChannel(Channel ch) throws Exception {
        ch.pipeline().addLast(new StringDecoder());
        ch.pipeline().addLast(new HelloHandler());
    }
}


使用 LineBasedFrameDecoder 按 换行符解码消息

public class LineBasedFrameDecoder extends ByteToMessageDecoder

A decoder that splits the received  ByteBuf s on line endings.Both "\n"  and "\r\n" are handled.

For a more general delimiter-based decoder, see  DelimiterBasedFrameDecoder