TCP粘包產(chǎn)生原因

1. 應(yīng)用程序write寫入的字節(jié)數(shù)大小大于套接字發(fā)送緩沖區(qū)的大小羔挡。
2. 進(jìn)行MSS大小的TCP分段玖姑。
3. 以太網(wǎng)幀的payload大于MTU進(jìn)行IP分片靠益。

用于解決TCP粘包問題的編碼器

1. LineBasedFrameDecoder -- 基于** 行 **的解碼器宣决。遍歷ByteBuf中的可讀字節(jié)，判斷是否有"\n"或"\r\n"吆你，如有則以此結(jié)束位置弦叶。可配置單行最大長度妇多，如達(dá)到最大長度伤哺，仍沒有發(fā)現(xiàn)換行符，則拋出異常者祖。(見代碼片段1)

// 代碼片段1
public class TimeServer {
    private class ChildChanneHandler extends ChannelInitiallizer<SocketChannel> {
        @override
        protected void initChannel(SocketChannel arg0) throws Execption { 
            arg0.pipeline().addLast ( new LineBasedFrameDecoder(1024));
            arg0.pipeline().addLast ( new StringDecoder());
            arg0.pipeline().addLast ( new TimeClientHandler());
        }
    }
}

2. StringDecoder -- 基于** 字符串 **的解碼器立莉。將接收到的byte[]轉(zhuǎn)換成字符串。LineBasedFrameDecoder+StringDecoder的組合即為按行切換的文本解碼器七问。
3. DelimiterBasedFrameDecoder -- 基于** 分隔符 **作為碼流結(jié)束標(biāo)示的消息解碼器蜓耻。(見代碼片段2)

// 代碼片段2
public class EchoServer {
    private class ChildChanneHandler extends ChannelInitiallizer<SocketChannel> {
        @override
        protected void initChannel(SocketChannel arg0) throws Execption { 
            ByteBuf delimiter = Unpooled.copiedBuffer("$_".getBytes()))
            arg0.pipeline().addLast ( new DelimiterBasedFrameDecoder(1024,delimiter));
            // arg0.pipeline().addLast ( new LineBasedFrameDecoder(1024));
            arg0.pipeline().addLast ( new StringDecoder());
            arg0.pipeline().addLast ( new TimeClientHandler());
        }
    }
}

4. FixedLengthFrameDecoder -- ** 固定長度 **解碼器.(見代碼片段3)

// 代碼片段3
public class EchoServer {
   private class ChildChanneHandler extends ChannelInitiallizer<SocketChannel> {
       @override
       protected void initChannel(SocketChannel arg0) throws Execption { 
           ByteBuf delimiter = Unpooled.copiedBuffer("$_".getBytes()))
           // arg0.pipeline().addLast ( new DelimiterBasedFrameDecoder(1024,delimiter));
           // arg0.pipeline().addLast ( new LineBasedFrameDecoder(1024));
           arg0.pipeline().addLast ( new FixedLengthFrameDecoder(20));
           arg0.pipeline().addLast ( new StringDecoder());
           arg0.pipeline().addLast ( new TimeClientHandler());
       }
   }
}