Android - Java - Transmitting / Receiving Hex Values

Question

I am new to the forums, and may have posted this to the wrong one - please help a newbie.

As part of project to develop Android App, I need to be able to connect from the app to a set location, which has a small microprocessor based(unchangable) LAN interface, which will accept set commands in hex. The response is given in hex.

Using a sample socket program, which I have tried to modify (see code below), I can see (using wireshark) that the transmitted string is in ASCII, not hex, so I am sending 38 bytes, and not the 18 with the 0x prefix.

I have tried using a LONG, but the value I am trying to send is too large (see String process = '0x.....' midway through the code), and I get 'The literal 0x.... of type int is out of range.

I would appreciate someone pointing me in the right direction.

Thanks

// package bdn;
/* The java.net package contains the basics needed for network operations. */
import java.net.*;
/* The java.io package contains the basics needed for IO operations. */
import java.io.*;
/** The SocketClient class is a simple example of a TCP/IP Socket Client.
* For a detailed explanation of the classes in this project see
* bdn.borland.com/article/0,1410,31995,00.html
*/

public class SocketClient 
{
    public static void main(String[] args) 
    {
        /** Define a host server */
        String host = "192.168.1.199";
        /** Define a port */
        int port = 3376;
        int i = 0;

        StringBuffer instr = new StringBuffer();
        // String TimeStamp;
        System.out.println("SocketClient initialized to " + host + ", port " + port );

        try 
        {
            /** Obtain an address object of the server */
            InetAddress address = InetAddress.getByName(host);
            /** Establish a socket connection */
            Socket connection = new Socket(address, port);
            /** Instantiate a BufferedOutputStream object */
            BufferedOutputStream bos = new BufferedOutputStream(connection.getOutputStream());

            /** Instantiate an OutputStreamWriter object with the optional character
            * encoding.
            */
            OutputStreamWriter osw = new OutputStreamWriter(bos, "US-ASCII");

            // TimeStamp = new java.util.Date().toString();
            String process = "0x308101000c00234C51050000000099670007";

            System.out.println("Data to be sent is " + process) ;

            /** Write across the socket connection and flush the buffer */
            osw.write(process);
            osw.flush();

            System.out.println("Data sent is " + process) ;

            /** Instantiate a BufferedInputStream object for reading
            * incoming socket streams.
            */

            BufferedInputStream bis = new BufferedInputStream(connection.getInputStream());
            /**Instantiate an InputStreamReader with the optional
            * character encoding.
            */

            InputStreamReader isr = new InputStreamReader(bis, "US-ASCII");

            /**Read the socket's InputStream and append to a StringBuffer */
            int c;
            for (i = 0; i <= 18; i++ ) 
            {
                c = isr.read() ;
                instr.append((char) c);
                System.out.println("character " + i + " value " + c);
            }

            /** Close the socket connection. */
            connection.close();
            System.out.println(instr);
        }
        catch (IOException f) 
        {
            System.out.println("IOException: " + f);
        }
        catch (Exception g) 
        {
            System.out.println("Exception: " + g);
        }
    }
}

Answer 1

I have tried using a LONG, but the value I am trying to send is too large

That's right. The value corresponds to

4225287479528688525220725405996728206163975

and the maximum value of a long is

9223372036854775807

You can store the number in a BigInteger as follows:

String process = "0x308101000c00234C51050000000099670007";
BigInteger bi = new BigInteger(process.substring(2), 16);