netty自定义解码器

/**
     * 一、netty本身提供了四种不同的解码器供用户使用，但并不能完全满足所有需求，这时就需要自定义解码器用于netty加载得到我们想要的数据。
     * demo是将tcp的流信息进行截取，ConstantValue.START_DATA = 0x40，ConstantValue.END_DATA = 0x23;
     * 截取为例如：十六进制 40 40 。。。。23 23 的数据包，用于实际应用或存储。
     * 代码如下：
     */

    protected void decode(ChannelHandlerContext ctx, ByteBuf buffer,
                          Listout) throws Exception {

        int beginReader = 0;
        while(buffer.isReadable()) {
            beginReader = buffer.readerIndex();
            buffer.markReaderIndex();
            buffer.resetReaderIndex();
            buffer.readByte();
            if(beginReader >= 0){
                if (((buffer.getByte(0) == ConstantValue.START_DATA))) {
                    if(beginReader >= 1) {
                        if (!((buffer.getByte(1) == ConstantValue.START_DATA))) {//如果第二位不是40，丢弃
                            buffer.discardReadBytes();
                            continue;
                        }
                    }
                } else {
                    buffer.discardReadBytes();
                    continue;
                }
            }
            if(beginReader > 2){
                if (!((buffer.getByte(beginReader) == ConstantValue.END_DATA) && (buffer.getByte(beginReader -1) == ConstantValue.END_DATA))) {
                    continue;
                } else {
                    int length = buffer.readerIndex();
                    byte[] data = new byte[length];

                    for(int i = 0; i < length; i++){
                        data[i] = buffer.getByte(i);
                    }
                    SmartCarProtocol protocol = new SmartCarProtocol(data.length, data);
                    out.add(protocol);
                    buffer.discardReadBytes();
                    break;
                }
            }
        }
        if (!((buffer.getByte(beginReader) == ConstantValue.END_DATA) && (buffer.getByte(beginReader -1) == ConstantValue.END_DATA))) {
            buffer.readerIndex(beginReader);  //收不到2323则返回继续
            return;
        }
}

// 对象类，用于存储数据
SmartCarProtocol 

public class SmartCarProtocol {
  
    private int head_data = ConstantValue.HEAD_DATA;  
      
    private int contentLength;  
      
    private byte[] content;  
  
      
    public SmartCarProtocol(int contentLength, byte[] content) {  
        this.contentLength = contentLength;  
        this.content = content;  
    }  
  
    public int getHead_data() {  
        return head_data;  
    }  
  
    public int getContentLength() {  
        return contentLength;  
    }  
  
    public void setContentLength(int contentLength) {  
        this.contentLength = contentLength;  
    }  
  
    public byte[] getContent() {  
        return content;  
    }  
  
    public void setContent(byte[] content) {  
        this.content = content;  
    }  
  
    @Override  
    public String toString() {  
        return "SmartCarProtocol [head_data=" + head_data + ", contentLength="  
                + contentLength + ", content=" + Arrays.toString(content);  
    }