Conversion to bytearray

Question

Hi there,
I have an special object of a self created type
Command data = Command();
into this object, i fill several values of int, long, and double type.
data.pI.Datatype; //int
data.pI.Command; //int
data.pI.Size; //long
data.dVal1; //double
1)What's the easiest way to create a byte array of this data 'object'?
I want to send this command to a server which is only able to understand unsigned bytes.
2)Is there a way e.g. if data.pI.Command contains 155 (as int) to generate a 4 byte big bytearray containing:
byte[0] =00000000
byte[0] =00000000
byte[0] =00000000
byte[0] =10011011
how does such type conversions to arrays work in general?
any help is greatly appreciated.
regards,
stonee

Answer 1

1)What's the easiest way to create a byte array of
this data 'object'?I assume you mean a single byte array that holds all of those values. See the code below.
I want to send this command to a server which is only
able to understand unsigned bytes.bytes are bytes. Unsigned is a way of interpreting them.
2)Is there a way e.g. if data.pI.Command contains 155
(as int) to generate a 4 byte big bytearray
containing:The code I am posting does all this using streams because I assumed you needed a solution that does both. I'm not guaranteeing this is the best way. If you need to set the values of Datatype, you'll need to write your own set method and call setByteArray() each time you change a value. Because of this, a different approach might be better. Two other ways are (1) use BigInteger class and (2) write your own code. There are examples you can find on the forums.
import java.io.*;
public class Test {
     private static int PACKET_SIZE=24;
     private static int DATATYPE_OFFSET=0;
     private static int COMMAND_OFFSET=4;
     private static int SIZE_OFFSET=8;
     private static int DVAL1_OFFSET=16;
     private byte[] bytes=null;
     private int Datatype=0;
     private int Command=0;
     private long Size=0;
     private double dVal1=0;
     private ByteArrayInputStream bStream=null;
     private DataInputStream dStream=null;
    public Test(int d,int c,long s, double dv) {
          Datatype=d;
          Command=c;
          Size=s;
          dVal1=dv;
          setByteArray();
     private void setByteArray() {
          try {
               ByteArrayOutputStream b=new ByteArrayOutputStream();
               DataOutputStream d=new DataOutputStream(b);
               d.writeInt(Datatype);
               d.writeInt(Command);
               d.writeLong(Size);
               d.writeDouble(dVal1);
               bytes=b.toByteArray();
               bStream=new ByteArrayInputStream(bytes);
               dStream=new DataInputStream(bStream);
               dStream.mark(PACKET_SIZE+1);
          } catch (Exception e) {;}
     public byte[] getBytes() {
          return bytes;
     public byte[] datatypeToByteArray() {
          return fieldToByteArray(DATATYPE_OFFSET,4);
     public byte[] commandToByteArray() {
          return fieldToByteArray(COMMAND_OFFSET,4);
     public byte[] sizeToByteArray() {
          return fieldToByteArray(SIZE_OFFSET,8);
     public byte[] dval1ToByteArray() {
          return fieldToByteArray(DVAL1_OFFSET,8);
/* offset is the number of bytes to reach the start of the field's value in the array.
*  size is the number of bytes in the field - 4 for int, 8 for long and double. */
     private byte[] fieldToByteArray(int offset,int size) {
          byte[] result=new byte[size];
          try {
               dStream.skip(offset);
               for(int i=0;i<result.length;i++)
                  result[ i ] = dStream.readByte();
               dStream.reset();
          } catch (Exception e) {;}
          return result;
    public static void show(byte[] b) {
          for(int i=0;i<b.length;i++)
               System.out.println(b[ i ]);
          System.out.println();
     public static void main(String[] args) throws Exception {
          Test t=new Test(0x01020304,0x05060708,0x090a0b0c0d0e0f10l,4.3);
          System.out.println("all");
          show(t.getBytes());
          System.out.println("Command");
          show(t.commandToByteArray());
          System.out.println("dval1");
          show(t.dval1ToByteArray());
          System.out.println("Datatype");
          show(t.datatypeToByteArray());
          System.out.println("size");
          show(t.sizeToByteArray());
}