How to get byte by byte from byte array

Question

I am getting response from server in string format like

V1YYZZ0x0000010x0D0x00112050x0C152031962061900x0D410240x0E152031962061900x0F410240x1021TATADOCOMOINTERNET101

Then I am converting it in to byte array because i need to get value from this byte by byte.

I tried to use

Arrays.copyOfRange(original,
                        from , to);

but it work on index basis not on byte basis.

I also tried following solution but it also truncating String(if I use string instead of byte[]) on length basis.

public static String truncateWhenUTF8(String s, int maxBytes) {
    int b = 0;
    for (int i = 0; i < s.length(); i++) {
        char c = s.charAt(i);

        // ranges from http://en.wikipedia.org/wiki/UTF-8
        int skip = 0;
        int more;
        if (c <= 0x007f) {
            more = 1;
        } else if (c <= 0x07FF) {
            more = 2;
        } else if (c <= 0xd7ff) {
            more = 3;
        } else if (c <= 0xDFFF) {
            // surrogate area, consume next char as well
            more = 4;
            skip = 1;
        } else {
            more = 3;
        }

        if (b + more > maxBytes) {
            return s.substring(0, i);
        }
        b += more;
        i += skip;
    }
    return s;
}

I know how to calculate string in byte length but it giving only full string length in byte like

Here is how I need to extract packet on byte basis.

Above codes and parameters is only example. I need to get byte by byte from string/byte array.

I searched lot but didn't get any solution or link which I can refer. I am not getting how to split string using byte length because I know byte length for each parameter and for value also.

Please give me any reference or hint.

Answer 1

This is not a answer to accessing a byte array byte by byte, but is an answer for the situation in which you find yourself.

Your explanation and description have the appearance of being confused as to what it is that you are really getting from the server (e.g. it is quite hard to represent "V1YYZZ0x0000010x0D0x001120" as a 9 byte field (note it probably ends on the 2, not the 0)). Alternately, that you are using the wrong method to get it from the server, or not getting it as the intended data type.

Your code indicates that you believe that what you are getting is a UTF8 string. The data shown in your question does not appear to indicate that it is intended to be in that format.

Keep in mind when doing something like this that some other programmer had to create structure for the data that you are seeing. They had to define it somewhere with the intent that it be able to be decoded by their intended recipients. Unless there are other considerations (security, minimal bandwidth, etc.), such formats are usually defined in a way that is both easy to encode and decode.

The existence of the multiple "0x"-ASCII-encoded hexadecimal numbers --particularly the single byte representing the parameter (called "varam" in your graphic)-- strongly implies that this data was intended to be interpreted as a ASCII encoded string. While that might not be the case, it should be kept in mind when looking at the problem from a larger perspective.

You are having to put too much effort into decoding the information you are getting from the server. It, probably, should be relatively easy unless there are considerations why it would have intentionally been made difficult.

All of this indicates that the real problem exists in an area for which you have provided us with no information.

Step back: Think about things like: How are you receiving this from the server (what function/interface)?
In the call requesting the information from the server is there a way to specify the encoding type be bytes, an ASCII string, or some other format that is easier to deal with than UTF8? At a minimum, it appears to be clear that the data was not intended to be handled as a UTF8 string. There should be a way for you to get it without it having been converted to UTF8.

Also, you should try to find an actual specification for the format of the data. You have not explained much about the source, so it may be you are reverse-engineering something and have no access to specifications.

Basically, it looks like this is a problem where it might be a good idea to step back and ask if you are starting from the point that makes it easiest to solve and if you are headed in the right direction for doing so.

Answer 2

I think it is doable with Scanner

import java.util.Scanner;

public class Library {

public static void main(String[] args) {
  String s = "V1YYZZ0x0000010x0D0x001120"
      + "50x0C152031962061900x0D410240x0E152031962061900x0F410240x1"
      + "021TATADOCOMOINTERNET101";

  // Skip first 9? bytes. I'm not sure how you define them
  // so I just assumed it is 26 chars long.
  s = s.substring(26, s.length());
  System.out.println(s);
  Scanner scanner = new Scanner(s);
  // Use byte as delimiter i.e. 0xDC, 0x00
  // Maybe you should use smth like 0x[\\da-fA-F]{2}
  // And if you want to know that byte, you should use
  // just 0x and get first 2 chars later
  scanner.useDelimiter("0x\\w{2}");
  // Easily extracted
  int numberOfParams = scanner.nextInt();
  for (int i = 0; i < numberOfParams; i++) {
      String extracted = scanner.next();
      // Length of message
      int l = extracted.length();
      boolean c = getLength(l) == getLength(l - getLength(l));
      l -= getLength(l);
      l = c ? l : l-1;

      System.out.println("length=" 
              + extracted.substring(0, extracted.length()-l));
      System.out.println("message=" 
              + extracted.substring(extracted.length()-l, extracted.length()));
  }
  // close the scanner
  scanner.close();
}
// Counting digits assuming number is decimal
private static int getLength(int l) {
    int length = (int) (Math.log10(l) + 1);
    System.out.println("counted length = " + length);
    return length;
}
}

We definitely need more information about rules, how string is formed. And what exactly you need to do. This code might be good enough you. And without comments it is really short and simple.

Answer 3

I'm sure I'm missing something obvious...

String.getBytes();

And if you want to process it in order taking defined objects from the array, just wrap using

ByteBuffer.wrap();

The result being something along the lines of:

String s = "OUTPUT FROM SERVER";
byte[] bytes = s.getBytes();
ByteBuffer bb = ByteBuffer.wrap(bytes);

What did I miss from the initial question? :/

Answer 4

To determine what is equal to one byte in a String is not trivial. Your String contains bytes in hexadecimal text form: 0x0D (one byte, equal to 13), but also contains values as substrings. For example 1024 can be interpreted as an integer which in this case fits into 2 bytes, but could also be interpreted as a text made up by 4 chars, totaling to 8 bytes.

Anyways, I would split the string using a regular expression, and then further split the parts to length and value:

String message = "V1YYZZ0x0000010x0D0x00112050x0C152031962061900x0D41024"+
    "0x0E152031962061900x0F410240x1021TATADOCOMOINTERNET101";
String regex = "(0)(x)(\\w\\w)";
String[] parts = message.split(regex);
Log.d(TAG,"HEADER = "+parts[0]);
for (int i=1; i<parts.length; i++) {
    String s = parts[i];
    // Only process if it has length > 0
    if (s.length()>0) {
        String len = "", val = "";
        // String s is now in format LVVVV where L is the length, V is the value
        if (s.length() < 11) {
            // 1 character indicates length, up to 9 contains value
            len = s.substring(0, 1);
            val = s.substring(1);
        } else if (s.length() > 10) {
            // 2 characters indicate length, up to 99 contains value
            len = s.substring(0, 2);
            val = s.substring(2);
        } else if (s.length() > 101) {
            // 3 characters indicate length, up to 999 contains value
            len = s.substring(0, 3);
            val = s.substring(3);
        }
        Log.d(TAG, "Length: " + len + " Value: " + val);
    }
}

This produces the following output:

D/Activity: HEADER = V1YYZZ
D/Activity: Length: 0 Value: 001
D/Activity: Length: 1 Value: 1205
D/Activity: Length: 15 Value: 203196206190
D/Activity: Length: 4 Value: 1024
D/Activity: Length: 15 Value: 203196206190
D/Activity: Length: 4 Value: 1024
D/Activity: Length: 21 Value: TATADOCOMOINTERNET101

Then you can check the packages (the first two package in the header is not needed), convert Strings to whatever you would like (e.g. Integer.parseInt(val))

If you explain the structure of the header (V1YYZZ0x0000010x0D0x0011205), I can improve my answer to find the message count.