code: public static NetFlowV9Header parseHeader(ByteBuf bb) {
          final int version = bb.readUnsignedShort();
          if (version != 9) {
              throw new InvalidFlowVersionException(version);
          }
  
          final int count = bb.readUnsignedShort();
          final long sysUptime = bb.readUnsignedInt();
          final long unixSecs = bb.readUnsignedInt();
          final long sequence = bb.readUnsignedInt();
          final long sourceId = bb.readUnsignedInt();
  
          return NetFlowV9Header.create(version, count, sysUptime, unixSecs, sequence, sourceId);
      }
docs: Flow Header Format
  
  <pre>
  |  0-1  |     version      |                                                                                                                                                                                                                                                                                                                                                                                              NetFlow export format version number                                                                                                                                                                                                                                                                                                                                                                                               |
  |-------|------------------|---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
  | 2-3   | count            | Number of flow sets exported in this packet, both template and data (1-30).                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                     |
  | 4-7   | sys_uptime       | Current time in milliseconds since the export device booted.                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                    |
  | 8-11  | unix_secs        | Current count of seconds since 0000 UTC 1970.                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                   |
  | 12-15 | package_sequence | Sequence counter of all export packets sent by the export device. Note: This is a change from the Version 5 and Version 8 headers, where this number represented total flows.                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                   |
  | 16-19 | source_id        | A 32-bit value that is used to guarantee uniqueness for all flows exported from a particular device. (The Source ID field is the equivalent of the engine type and engine ID fields found in the NetFlow Version 5 and Version 8 headers). The format of this field is vendor specific. In Cisco's implementation, the first two bytes are reserved for future expansion, and will always be zero. Byte 3 provides uniqueness with respect to the routing engine on the exporting device. Byte 4 provides uniqueness with respect to the particular line card or Versatile Interface Processor on the exporting device. Collector devices should use the combination of the source IP address plus the Source ID field to associate an incoming NetFlow export packet with a unique instance of NetFlow on a particular device. |
  </pre>