Netty分布式固定长度解码器实现原理剖析

public class FixedLengthFrameDecoder extends ByteToMessageDecoder {

     //长度大小

     private final int frameLength;

     public FixedLengthFrameDecoder( int frameLength) {

         if (frameLength <= 0 ) {

             throw new IllegalArgumentException(

                     "frameLength must be a positive integer: " + frameLength);

         }

         //保存当前frameLength

         this .frameLength = frameLength;

     }

     @Override

     protected final void decode(ChannelHandlerContext ctx, ByteBuf in, List<Object> out) throws Exception {

         //通过ByteBuf去解码.解码到对象之后添加到out上

         Object decoded = decode(ctx, in);

         if (decoded != null ) {

             //将解析到byteBuf添加到对象里面

             out.add(decoded);

         }

     }

     protected Object decode(

             @SuppressWarnings ( "UnusedParameters" ) ChannelHandlerContext ctx, ByteBuf in) throws Exception {

         //字节是否小于这个固定长度

         if (in.readableBytes() < frameLength) {

             return null ;

         } else {

             //当前累加器中截取这个长度的数值

             return in.readRetainedSlice(frameLength);

         }

     }

}