public ByteBuffer encode() {
    // 1> header length size
    int length = 4;
    // 2> header data length
    byte[] headerData = this.headerEncode();
    length += headerData.length;
    // 3> body data length
    if (this.body != null) {
        length += body.length;
    }
    ByteBuffer result = ByteBuffer.allocate(4 + length);
    // 1.先放入消息的总大小
    result.putInt(length);
    // 2.再放入头部的长度
    result.put(markProtocolType(headerData.length, serializeTypeCurrentRPC));
    // 3.接着放入头部数据
    result.put(headerData);
    // 4.最后放入消息体的数据
    if (this.body != null) {
        result.put(this.body);
    }
    result.flip();
    return result;
}

private byte[] headerEncode() {
    this.makeCustomHeaderToNet();
    if (SerializeType.ROCKETMQ == serializeTypeCurrentRPC) {
        return RocketMQSerializable.rocketMQProtocolEncode(this);
    } else {
        return RemotingSerializable.encode(this);
    }
}

    public static byte[] markProtocolType(int source, SerializeType type) {
        byte[] result = new byte[4];
        result[0] = type.getCode();
        result[1] = (byte) ((source >> 16) & 0xFF);
        result[2] = (byte) ((source >> 8) & 0xFF);
        result[3] = (byte) (source & 0xFF);
        return result;
    }

public static RemotingCommand decode(final ByteBuffer byteBuffer) {
    int length = byteBuffer.limit();// 获取byteBuffer的总长度
    int oriHeaderLen = byteBuffer.getInt();// 1.获取前4个字节，组装int类型，该长度为总长度 图中 length
    int headerLength = getHeaderLength(oriHeaderLen);// length & 0xFFFFFF 获取消息头的长度，与运算，编码时候的长度即为24位
    byte[] headerData = new byte[headerLength];// 保存header data
    byteBuffer.get(headerData);// 2.从缓冲区中读取headerLength个字节的数据，这个数据就是报文头部的数据
    RemotingCommand cmd = headerDecode(headerData, getProtocolType(oriHeaderLen));
    int bodyLength = length - 4 - headerLength;// 报文体的数据，减去了第二、三部分的长度
    byte[] bodyData = null;
    if (bodyLength > 0) {
        bodyData = new byte[bodyLength];
        byteBuffer.get(bodyData);// 获取消息体的数据
    }
    cmd.body = bodyData;
    return cmd;
}

private static RemotingCommand headerDecode(byte[] headerData, SerializeType type) {
    switch (type) {
        case JSON:
            RemotingCommand resultJson = RemotingSerializable.decode(headerData, RemotingCommand.class);
            resultJson.setSerializeTypeCurrentRPC(type);
            return resultJson;
        case ROCKETMQ:
            RemotingCommand resultRMQ = RocketMQSerializable.rocketMQProtocolDecode(headerData);
            resultRMQ.setSerializeTypeCurrentRPC(type);
            return resultRMQ;
        default:
            break;
    }
    return null;
}

public static int getHeaderLength(int length) {
    return length & 0xFFFFFF;// 为什么是和高位的24位与，可以参考编码时的方法：markProtocolType
}