how to write bytes to server socket

问题

I'm writing a java socket program to read data from server, I've no control to server, below is protocol agreed,

2-bytes: magic number
2-bytes: data length
N-bytes: ASCII string data payload
Big endian for the magic number and data length

For Example: if my request is "command/1/getuserlist" how to construct th request match above protocol and read the response back to List

I'm new to socket programming and have no idea how to build my request and read the response back.

can someone guide me how to build the request and read the response from

回答1:

According to the specification you must build a packet shaped in the following way

| 2 | 2 | N ........ |

Now this could be quite easy and there are multiple ways to do it, I suggest you one:

import java.nio.ByteBuffer;
import java.nio.ByteOrder;

static byte[] buildPacket(int magicNumber, String payload) throws UnsupportedEncodingException
{
  // 4 bytes for header + payload
  ByteBuffer buffer = ByteBuffer.allocate(2 + 2 + payload.length());
  // we set that we want big endian numbers
  buffer.order(ByteOrder.BIG_ENDIAN);

  buffer.putShort((short)magicNumber);
  buffer.putShort((short)payload.length());
  buffer.put(payload.getBytes("US-ASCII"));
  return buffer.array();
}

public static void main (String[] args) throws java.lang.Exception
{
    try
    {
        byte[] bytes = buildPacket(0xFF10, "foobar");
        for (byte b : bytes)
          System.out.printf("0x%02X ", b);
    }
    catch (Exception e)
    {
        e.printStackTrace();
    }
}

Mind that if you declare the method to accept a short magic number directly, you won't be able to pass a literal magic number > 32767 because short is signed in Java.

回答2:

Use a DataOutputStream around a BufferedOutputStream around the `Socket.getOutputStream(). Then you can use:

writeShort() for the magic number
writeShort() for the length word
write() for the payload.

Similarly you can use DataInputStream and the corresponding readXXX() methods to read the response.

NB You are writing to a socket here, not a server socket.

回答3:

Watch out for the big endinanness!

DataxxxStream - although it is quite handy - does not offer a full support for both little and big endian numbers and arbitrary String encodings.

See my post at How to Read Byte Stream from Socket

来源：https://stackoverflow.com/questions/35952184/how-to-write-bytes-to-server-socket

标签

java

sockets

serversocket