Encoding Integers Into an Existing Byte Array

[mesagreg]

I am trying to write a method that takes a byte array as an input, appends a 3-byte header onto the array and sends the resulting byte array to a remote host via an OutputStream.

My method signature is something like this:

public void write(byte[] data)
{
byte [] packet = new byte[data.length + 3];
packet = System.arraycopy(data,0,header,header.length)
packet[0] = 3; //<--- I just need to encode the integer 3
packet[1] = 0;
packet[2] = packet.length;<---I need to encode the
length of the packet here
}
My problem is that I don't know how to encode the integer values into the bytes. And I'm not sure if the arraycopy will work correctly.

Can anyone advise me on this?
Thanks,


Gregory A. Lusk, P.E., CCNA

 

[toolkit]

There are a few approaches:

[1] cast your integers to bytes, for example:

    packet[2] = (byte)packet.length;

[2] use a ByteArrayOutputSteam, for example:

    import java.io.ByteArrayOutputStream;
    byte[] data = { 1,2,3,4,5 };
    ByteArrayOutputStream out = new ByteArrayOutputStream();
    out.write(3);
    out.write(0);
    out.write((byte)(data.length+3));
    out.write(data, 0, data.length);
    data = out.toByteArray();
    for(int i = 0; i < data.length ; i++)
      System.out.println(data[i]);

[3] use a DataOutputStream, for example:

    import java.io.FileOutputStream;
    import java.io.DataOutputStream;

    byte[] data = { 1,2,3,4,5 };
    try {
      DataOutputStream out = new DataOutputStream(
        new FileOutputStream("data"));
      out.write(3);
      out.write(0);
      out.write((byte)(data.length+3));
      for(int i = 0; i < data.length ; i++)
        out.write(data[i]);
      out.flush();
      out.close();
    } catch(Exception e) {
      e.printStackTrace();
    }

[4] In Java 1.4, you can use the new packages java.nio, and java.nio.channels. See:

http://java.sun.com/j2se/1.4/docs/api/java/nio/package-summary.html

http://java.sun.com/j2se/1.4/docs/api/java/nio/channels/package-summary.html

Hope this helps. Cheers, Neil

 

[mesagreg]

Toolkit,

Thanks so much for your post. I am fairly new to Java, coming over from the .NET world. I know how to accomplish the task using VB or C#, but didn't know how to do it in Java.

Thanks,
Gregory A. Lusk, P.E., CCNA