将字节数组转换为整数数组以通过Java套接字发送

Question

Hi I am new to Java development and have the following problem.

I construct a char array with the values {130,56,0,0,2,0,0,0}. I then pass that values into a String using String.valueOf(), once that is done I convert the sting into a byte array using getBytes() function.

I use a DataOutputStream writer to write the data to socket. My problem lies in the fact that on tcp level using wireshark to trace the data I am actuality sending c2 82 38 00 00 02 00 00 00 on the wire and not the original 130 56 0 0 2 0 0 0 .

Code snippet below

public void run() {
        System.out.println("Got a client !");
        try {
            // Accept Loop while connected
            while (true) {
                byte[] arrOutut = new byte[4096];
                int count = clientSocket.getInputStream().read(arrOutut, 0, 4096);
                String clientRequest = "";
                System.out.println("packet size is  " + count + "\n");
                if (count != -1) {
                    for (int outputCount = 0; outputCount < count; outputCount++) {
                        char response = (char) arrOutut[outputCount];
                        clientRequest = clientRequest + response;
                    }
                    System.out.println("Got a clientrequest "+ clientRequest + "\n");
                    count = 0;

                } else {
                    break;
                }

                char[] Map = new char[]{130,56,0,0,2,0,0,0};

                String StringMsg = String.valueOf(Map, 0, Map.length);

                byte[] data = StringMsg.getBytes();
                byte[] asciidata = StringMsg.getBytes("ASCII");

                System.out.println("Byte Data "+ data); 
                System.out.println("Byte Data ACII" + asciidata);

                OutputStream dOut = clientSocket.getOutputStream();
                DataOutputStream dos = new DataOutputStream(dOut);
                int sendDataLength = data.length;

                dos.write(data, 0, sendDataLength);
                dos.flush();


            }
            clientSocket.close();
            } catch (SocketTimeoutException e) {
            System.out.println("Connection timed out");
        } catch (IOException e) {
            throw new RuntimeException(e);
        }
    }

Is there anyway I send 130 56 0 0 2 0 0 0 on the wire using java socket writer

Say for argument sake the following is necessary

String StringMsg = String.valueOf(Map, 0, Map.length);

                byte[] data = StringMsg.getBytes();

Answer 1

A char is not meant to store binary data . Yes, in C, it stores a signed, 8 bit integral number; in Java, however, a char is a UTF16 code unit.

You want byte here; more specifically, you want a ByteBuffer :

final ByteBuffer buf = ByteBuffer.allocate(8);

buf.put((byte) 130);
// etc etc

// send buf.array() on the wire; or use a SocketChannel and use buf directly

And yes, it is a pain to have to cast to a byte each time, but then this is how it is :/

---

Also, a lot of people are confused by this (I was when I began with Java coming from C), but the fact that primitive types are unsigned does not matter at all; bits remain bits. For instance, byte -128 (or Byte.MIN_VALUE ) is 1111 1111 . Unless you have to perform arithmetic operations on numbers, the fact that a primitive is negative or not has no influence at all. And by the way, this is also why Java has two operators for left byte shifting, >> and >>> (the second one does not "carry" the sign bit).

By the way, Java primitive types are big endian -- even if the underlying architecture isn't.

Answer 2

you have to understand the difference between a hexadecimal A and the character A . The Hex A refers to the binary value 1010 where as the Character A does not. With that in mind if you are gonna store your bytes just use a byte array or ByteBuffer

Answer 3

I construct a char array with the values {130,56,0,0,2,0,0,0}.

Why?

I then pass that values into a String using String.valueOf()

Why? String is not a container for binary data.

once that is done I convert the sting into a byte array using getBytes() function.

Why?

Why not construct the original data straight into a byte array and cut the whole palaver?

I use a DataOutputStream writer

DataOutputStream is a stream, not a Writer.

to write the data to socket. My problem lies in the fact that on tcp level using wireshark to trace the data I am actuality sending c2 82 38 00 00 02 00 00 00 on the wire and not the original 130 56 0 0 2 0 0 0 .

Exactly as predicted. So why not send the original data as a byte array, and cut out several error prone steps?