ByteBuffer Missing Data When decoded As string

Question

I'm reading and writing to a ByteBuffer

import org.assertj.core.api.Assertions;

import java.io.IOException;
import java.net.InetSocketAddress;
import java.nio.ByteBuffer;
import java.nio.ByteOrder;
import java.nio.charset.Charset;
import java.nio.charset.CharsetDecoder;
import java.nio.charset.CharsetEncoder;

public class Solution{
public static void main(String[] args) throws Exception{

    final CharsetEncoder messageEncoder = Charset.forName("ISO-8859-1").newEncoder();
    String message = "TRANSACTION IGNORED";
    String carrierName= "CARR00AB";
    int messageLength = message.length()+carrierName.length()+8;


    System.out.println(" --------Fill data---------");
    ByteBuffer messageBuffer = ByteBuffer.allocate(4096);
    messageBuffer.order(ByteOrder.BIG_ENDIAN);
    messageBuffer.putInt(messageLength);
    messageBuffer.put(messageEncoder.encode(CharBuffer.wrap(carrierName)));
    messageBuffer.put(messageEncoder.encode(CharBuffer.wrap(message)));
    messageBuffer.put((byte) 0x2b);
    messageBuffer.flip();

    System.out.println("------------Extract Data Approach 1--------");

    CharsetDecoder messageDecoder = Charset.forName("ISO-8859-1").newDecoder();
    int lengthField = messageBuffer.getInt();
    System.out.println("lengthField="+lengthField);
    int responseLength = lengthField - 12;
    System.out.println("responseLength="+responseLength);
    String messageDecoded= messageDecoder.decode(messageBuffer).toString();
    System.out.println("messageDecoded="+messageDecoded);
    String decodedCarrier = messageDecoded.substring(0, carrierName.length());
    System.out.println("decodedCarrier="+ decodedCarrier);
    String decodedBody = messageDecoded.substring(carrierName.length(), messageDecoded.length() - 1);
    System.out.println("decodedBody="+decodedBody);

    Assertions.assertThat(messageLength).isEqualTo(lengthField);
    Assertions.assertThat(decodedBody).isEqualTo(message);
    Assertions.assertThat(decodedBody).isEqualTo(message);

    ByteBuffer messageBuffer2 = ByteBuffer.allocate(4096);
    messageBuffer2.order(ByteOrder.BIG_ENDIAN);
    messageBuffer2.putInt(messageLength);
    messageBuffer2.put(messageEncoder.encode(CharBuffer.wrap(carrierName)));
    messageBuffer2.put(messageEncoder.encode(CharBuffer.wrap(message)));
    messageBuffer2.put((byte) 0x2b);
    messageBuffer2.flip();

    System.out.println("---------Extract Data Approach 2--------");

    byte [] data = new byte[messageBuffer2.limit()];
    messageBuffer2.get(data);
    String dataString =new String(data, "ISO-8859-1");
    System.out.println(dataString);

}
}

It works fine but then I thought to refactor it, Please see approach 2 in above code

    byte [] data = new byte[messageBuffer.limit()];
    messageBuffer.get(data);
    String dataString =new String(data, "ISO-8859-1");
    System.out.println(dataString);

 Output=     #CARR00ABTRANSACTION IGNORED+

Could you guys help me with explanation

why the integer is got missing in second approach while decoding ???
Is there any way to extract the integer in second approach??

Without reading the question, Have you provided an encoding? — SamHoque
– SamHoque, Commented Dec 13, 2018 at 12:00
Okay, I will compile the code my side and verify the issue if someone else hasn't already before me. — SamHoque
– SamHoque, Commented Dec 13, 2018 at 12:01
Where did you place your last code? Can you provide working example? — SamHoque
– SamHoque, Commented Dec 13, 2018 at 12:05
see updates , please remove Assertions before executing code — edwin
– edwin, Commented Dec 13, 2018 at 12:13

SamHoque · Accepted Answer · 2018-12-13 18:38:01Z

1

Okay so you are trying to read an int from the Buffer which takes up 4 bits and then trying to get the whole data after reading 4 bits

What I have done is call messageBuffer2.clear(); after reading the int to resolve this issue. here is the full code

System.out.println(messageBuffer2.getInt());
byte[] data = new byte[messageBuffer2.limit()];
messageBuffer2.clear();
messageBuffer2.get(data);
String dataString = new String(data, StandardCharsets.ISO_8859_1);
System.out.println(dataString);

Output is:

35
   #CARR0033TRANSACTION IGNORED+

Edit: So basically when you are calling clear it resets various variables and it also resets the position it's getting from and thats how it fixes it.

edited Dec 13, 2018 at 18:38

answered Dec 13, 2018 at 12:39

SamHoque

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1 Comment

edwin Over a year ago

Can you please explain how(logic behind) calling 'clear' fix this issue ??

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