Netty使用解碼器Decoder解決TCP粘包和拆包問題

解碼器Decoder和ChannelHandler的關系

netty的解碼器通常是繼承自ByteToMessageDecoder，而它又是繼承自ChannelInboundHandlerAdapter，其實也是一種ChannelHandler和我們自定義的ChannelHandler一樣都是來處理進入或者出去的數據。常用的幾種解碼器有：

• LineBasedFrameDecoder
• DelimiterBasedFrameDecoder
• FixedLengthFrameDecoder

LineBasedFrameDecoder

LineBasedFrameDecoder 行解碼器，遍歷ByteBuf中的可讀字節，按行（\n \r\n）處理

StringDecoder

StringDecoder將接受的碼流轉換為字符串

代碼中使用

    @Override
    protected void initChannel(SocketChannel ch) throws Exception {
        ChannelPipeline pipeline = ch.pipeline();
        //LineBasedFrameDecoder遍歷ByteBuf中的可讀字節，按行（\n \r\n）處理
        pipeline.addLast(new LineBasedFrameDecoder(1024));
        //StringDecoder將接受的碼流轉換為字符串
        pipeline.addLast(new StringDecoder());
        pipeline.addLast(new NettyServerHandler());
    }

NettyServerHandler處理類中讀取,String message = (String) msg;直接轉換為String：

    private int count = 0;
    @Override
    public void channelRead(ChannelHandlerContext ctx, Object msg) throws Exception {
        String message = (String) msg;
        LOGGER.info("client received message {}：{}", ++count, message);
    }

DelimiterBasedFrameDecoder

DelimiterBasedFrameDecoder,將特定分隔符作為碼流結束標志的解碼器。

代碼中使用

    @Override
    protected void initChannel(SocketChannel ch) throws Exception {
        ChannelPipeline pipeline = ch.pipeline();
        ByteBuf byteBuf = Unpooled.copiedBuffer("$_".getBytes());
        pipeline.addLast(new DelimiterBasedFrameDecoder(1024,true,true,byteBuf));
        pipeline.addLast(new StringDecoder());
        pipeline.addLast(new NettyServerHandler());
    }

FixedLengthFrameDecoder

FixedLengthFrameDecoder 固定長度解碼器，只會讀取指定長度的碼流。

代碼中使用

    @Override
    protected void initChannel(SocketChannel ch) throws Exception {
        ChannelPipeline pipeline = ch.pipeline();
        pipeline.addLast(new FixedLengthFrameDecoder(24));
        pipeline.addLast(new StringDecoder());
        pipeline.addLast(new NettyServerHandler());
    }