Converting byte array to String and String to byte array in Java

Question

I converted byte array bytes to String. But when calculating the bytes in the string, I am not getting correct answer. The size of bytes is 125, but I'm getting 129. The code is given below:

    String s2= null;
    try {

        System.out.println(bytes.length);           //This gives 125 as answer
        s2 = new String(bytes,"UTF-8");
        System.out.println(s2.getBytes("UTF-8").length); //But this gives 129 instead of 125
   } 
    catch (UnsupportedEncodingException e) {
        e.printStackTrace();
    }

What is wrong with above code?

EDIT: Based on the answers given below, bytes is encoded in the wrong format. If initialization of bytes done as shown below, then how to convert bytes to string without losing(or gaining) any extra data?

byte[] bytes=new byte[125];
    for (int i = 0; i < 125; i++) {       
        bytes[bytes.length - i / 8 - 1] |= 1 << (i % 8);
     }

Update: If I remove the shift operation in above code it is giving correct output. What is the problem with shifting?

That is probably due to an encoding error in the original bytes. Can you give us the original byte array? — Dani
– Dani, Commented Oct 28, 2013 at 18:11
I get 125 when I run your code with byte[] bytes = new byte[125]; — jonhopkins
– jonhopkins, Commented Oct 28, 2013 at 18:12

Mike Thomsen · Accepted Answer · 2013-10-28 18:12:10Z

2

It's possible that s2 = new String(bytes,"UTF-8"); added additional bytes because the original string was not UTF-8.

answered Oct 28, 2013 at 18:12

Mike Thomsen

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Comments

Kiran · Accepted Answer · 2013-10-28 19:46:25Z

1

Upon further investigating my code, I found that bytes array contains negative values. If a byte array contains negative values, using UTF-8 encoding will add extra characters in the resulting string. That's why when I converted this string back to byte array extra characters are introduced thus increasing the byte array length.

Using encoding method ISO-8859-1 solved my problem.

Thank you all for suggestions.

answered Oct 28, 2013 at 19:46

Kiran

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Comments

Joachim Sauer · Accepted Answer · 2013-10-28 18:20:29Z

0

The code you posted should work, provided the data in bytes is actually UTF-8 encoded.

It will not work, it the data in bytes is anything else (except maybe an UTF-8-compatible encoding such as ASCII).

That is because not every possible sequence of bytes is a valid UTF-8 sequence. And when one of the invalid sequences is encountered, then it will be replaced with the Unicode replacement character. Converting that back to bytes will not reproduce the original bytes.

You seem to have a deeper issue here: what is bytes and why do you want to convert it to a String in the first place?

answered Oct 28, 2013 at 18:20

Joachim Sauer

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7 Comments

Kiran Over a year ago

Thank you. May be bytes was not "UTF-8" encoded. Is there any way to know it's encoding?

Joachim Sauer Over a year ago

@Kiran: there's no sure way without knowing where it comes from. You can guess, but the best way is to ask whoever/whatever provided it to you. Where did they come from?

Kiran Over a year ago

bytes are initialized with random integers less than 100. Can you tell me what to do in this case?

Kiran Over a year ago

I edited my question now. It contains initialization of bytes. Can you tell me what is the correct way to convert this bytes to Stirng?

Joachim Sauer Over a year ago

@Kiran: well, what do you expect the String to contain? The numbers in decimal form? "random integers less than 100" will not produce a usable String when interpreting them using any common encoding (it will some letters and digits, but many control characters as well).

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