在netty中配置Decoder一定注意相互的影響

   protected void initChannel(SocketChannel socketChannel)  {
        ChannelPipeline pipeline = socketChannel.pipeline();
        ByteBuf delimiter = Unpooled.copiedBuffer("$".getBytes());
        pipeline.addLast(new CustomFrameDecoder(1000, delimiter));
        pipeline.addLast
 
(new HttpRequestDecoder());
        pipeline.addLast(DECODER);
        pipeline.addLast(ENCODER);
        pipeline.addLast(new IdleStateHandler(5, 0, 0, TimeUnit.SECONDS));
        pipeline.addLast(nettyServerHandler);
    }

這裡本人自定義的Decoder 和HttpRequestDecoder衝突 當配置HttpRequestDecoder時自定義的Decoder返回的資料並未返回到ChannelRead

## 自定義Decoder 獲取以$符為開頭4位數字為數的頭，資料體的位數是頭中4位數的length ##

package com.llvision.netty.decoder;

import io.netty.buffer.ByteBuf;
import io.netty.buffer.Unpooled;
import io.netty.channel.ChannelHandlerContext;
import io.netty.handler.codec.ByteToMessageDecoder;
import io.netty.handler.codec.TooLongFrameException;
import
 
 org.slf4j.Logger;
import org.slf4j.LoggerFactory;

import java.util.List;

/**
 * @author yd
 * 2017/04/08
 */
public class CustomFrameDecoder  extends ByteToMessageDecoder {
    private final Logger logger= LoggerFactory.getLogger(CustomFrameDecoder.class);
    private static int HEADER_SIZE = 4;
    private final ByteBuf[] delimiters;
    private final int maxFrameLength;
    private final boolean stripDelimiter=true;
    private final boolean failFast=true;
    private boolean discardingTooLongFrame;
    private static ByteBuf buf = Unpooled.buffer();
    private int tooLongFrameLength;

    public CustomFrameDecoder(int maxFrameLength,ByteBuf delimiter ) {
        this(maxFrameLength,new ByteBuf[]{delimiter.slice(delimiter.readerIndex(), delimiter.readableBytes())});
    }

    public CustomFrameDecoder(int maxFrameLength, ByteBuf... delimiters ) {
        if(delimiters == null) {
            throw new NullPointerException("delimiters");
        } else if(delimiters.length == 0) {
            throw new IllegalArgumentException("empty delimiters");
        } else {
            this.delimiters = new ByteBuf[delimiters.length];
            for (int i = 0; i < delimiters.length; ++i) {
                ByteBuf d = delimiters[i];
                validateDelimiter(d);
                this.delimiters[i] = d.slice(d.readerIndex(), d.readableBytes());
            }
            this.maxFrameLength = maxFrameLength;
        }
    }

    @Override
    protected void decode(ChannelHandlerContext ctx, ByteBuf in, List<Object> out) throws Exception {
        Object decoded = this.decode(ctx, in);
        if(decoded != null) {
            out.add(decoded);
        }
    }

    protected Object decode(ChannelHandlerContext ctx, ByteBuf buffer) {
        try{
            int minFrameLength = 2147483647;
            ByteBuf minDelim = null;
            ByteBuf[] minDelimLength = this.delimiters;
            int frame = minDelimLength.length;
            int tooLongFrameLength;
            for(tooLongFrameLength = 0; tooLongFrameLength < frame; ++tooLongFrameLength) {
                ByteBuf delim = minDelimLength[tooLongFrameLength];
                int frameLength = indexOf(buffer, delim);
                if(frameLength >= 0 && frameLength < minFrameLength) {
                    minFrameLength = frameLength;
                    minDelim = delim;
                }
            }
            if(minDelim != null) {
                int var10 = minDelim.capacity();
                if(this.discardingTooLongFrame) {
                    this.discardingTooLongFrame = false;
                    buffer.skipBytes(minFrameLength + var10);
                    tooLongFrameLength = this.tooLongFrameLength;
                    this.tooLongFrameLength = 0;
                    if(!this.failFast) {
                        this.fail((long)tooLongFrameLength);
                    }
                    return null;
                } else if(minFrameLength > this.maxFrameLength) {
                    buffer.skipBytes(minFrameLength + var10);
                    this.fail((long)minFrameLength);
                    return null;
                } else {
                    //如果buffer的中小於5表達根本不可能有頭的位置，所以跳過
                    if(buffer.readableBytes()<=5){return null;}
                    int bodyLength=bodyLenght(buffer);
                    ByteBuf var11;
                    if((bodyLength+5)<=buffer.readableBytes()){
                        if(this.stripDelimiter) {
                            buffer.skipBytes(minFrameLength+5);
                            var11 = buffer.readRetainedSlice(bodyLength);
                        } else {
                            buffer.skipBytes(5);
                            var11 = buffer.readRetainedSlice(bodyLength + var10);
                            buffer.skipBytes(bodyLength);
                        }
                    }else{
                        return null;
                    }
                    return var11;
                }
            } else {
                if(!this.discardingTooLongFrame) {
                    if(buffer.readableBytes() > this.maxFrameLength) {
                        this.tooLongFrameLength = buffer.readableBytes();
                        buffer.skipBytes(buffer.readableBytes());
                        this.discardingTooLongFrame = true;
                        if(this.failFast) {
                            this.fail((long)this.tooLongFrameLength);
                        }
                    }
                } else {
                    this.tooLongFrameLength += buffer.readableBytes();
                    buffer.skipBytes(buffer.readableBytes());
                }
                return null;
            }
        }catch (Exception e){
            e.printStackTrace();
            return null;
        }
    }


    private static int indexOf(ByteBuf haystack, ByteBuf needle) {
        for(int i = haystack.readerIndex(); i < haystack.writerIndex(); ++i) {
            int haystackIndex = i;
            int needleIndex;
            for(needleIndex = 0; needleIndex < needle.capacity() && haystack.getByte(haystackIndex) == needle.getByte(needleIndex); ++needleIndex) {
                ++haystackIndex;
                if(haystackIndex == haystack.writerIndex() && needleIndex != needle.capacity() - 1) {
                    return -1;
                }
            }
            if(needleIndex == needle.capacity()) {
                return i - haystack.readerIndex();
            }
        }

        return -1;
    }

    /**
     * 功能：獲取資訊頭中的長度
     * */
    private  int bodyLenght(ByteBuf buf){
        int bodyLength=0;
        int headerIndex=buf.readerIndex()+1,headerEnd=buf.readerIndex()+4;
        for(;headerIndex<=headerEnd;headerIndex++){
            bodyLength*=10;
            bodyLength+=(int)buf.getByte(headerIndex)-48;
        }
        return bodyLength;
    }

    private void fail(long frameLength) {
        if(frameLength > 0L) {
            throw new TooLongFrameException("frame length exceeds " + this.maxFrameLength + ": " + frameLength + " - discarded");
        } else {
            throw new TooLongFrameException("frame length exceeds " + this.maxFrameLength + " - discarding");
        }
    }

    private static void validateDelimiter(ByteBuf delimiter) {
        if(delimiter == null) {
            throw new NullPointerException("delimiter");
        } else if(!delimiter.isReadable()) {
            throw new IllegalArgumentException("empty delimiter");
        }
    }
}