In Java, how do I deal with UDP messages that are

问题:

I read this question about the error that I'm getting and I learned that UDP data payloads can't be more than 64k. The suggestions that I've read are to use TCP, but that is not an option in this particular case. I am interfacing with an external system that is transmitting data over UDP, but I don't have access to that external system at this time, so I'm simulating it.

I have data messages that are upwards of 1,400,000 bytes in some instances and it's a requirement that the UDP protocol is used. I am not able to change protocols (I would much rather use TCP or a reliable protocol build on UDP). Instead, I have to find a way to transmit large payloads over UDP from a test application into the system that I am building and to read those large payloads in the system that I'm building for processing. I don't have to worry about dropped packets, either - if I don't get the datagram, I don't care - just wait for the next payload to arrive. If it's incomplete or missing, just throw it all away and continue waiting. I also don't know the size of the datagram in advance (they range of a few hundred bytes to 1,400,000+ bytes.

I've already set my send and receive buffer sizes large enough, but that's not sufficient. What else can I do?

回答1:

UDP packets have a 16 bit length field. It's nothing to do with Java. They cannot be bigger, period. If the server you are talking to is immutable, you are stuck with what you can fit into a packet.

If you can change the server and thus the protocol, you can more or less reimplement TCP for yourself. Since UDP is defined to be unreliable, you need the full retransmission mechanism to cope with packets that are dropped in the network somewhere. So, you have to split the 'message' into chunks, send the chunks, and have a protocol for requesting retransmission of lost chunks.

回答2:

It's a requirement ...

The requirement should also therefore dictate the packetization technique. You need more information about the external system and its protocol. Note that the maximum IPv4 UDP payload Is 65535-28 bytes, and the maximum practical payload is < 1500 bytes once a router gets involved.