Convert byte array to understandable String

Question

I have a program that handles byte arrays in Java, and now I would like to write this into a XML file. However, I am unsure as to how I can convert the following byte array into a sensible String to write to a file. Assuming that it was Unicode characters I attempted the following code:

String temp = new String(encodedBytes, "UTF-8");

Only to have the debugger show that the encodedBytes contain "\ufffd\ufffd ^\ufffd\ufffd-m\ufffd\ufffd\/ufffd \ufffd\ufffdIA\ufffd\ufffd". The String should contain a hash in alphanumerical format.

How would I turn the above String into a sensible String for output?

"Understandable" or "sensible" to whom? Is the goal to output so that a human can understand the values or is the goal to output it to a format that can be read back in and transformed back into a byte array? — Bert F
– Bert F, Commented Apr 16, 2010 at 15:40
Would serialization (Arrays in Java are serializable) work? See e.g. rgagnon.com/javadetails/java-0470.html — Searles
– Searles, Commented Apr 16, 2010 at 16:25
@Bert F: For arguments sake, let's say that the human-readable output is "2jvjsgjlgj39hg9". I would like to convert the string in the question to that string so that it can be both read by humans and stored. — Mike B
– Mike B, Commented Apr 16, 2010 at 16:42

trashgod · Accepted Answer · 2010-04-16 21:49:07Z

The byte array doesn't look like UTF-8. Note that \ufffd (named REPLACEMENT CHARACTER) is "used to replace an incoming character whose value is unknown or unrepresentable in Unicode."

Addendum: Here's a simple example of how this can happen. When cast to a byte, the code point for ñ is neither UTF-8 nor US-ASCII; but it is valid ISO-8859-1. In effect, you have to know what the bytes represent before you can encode them into a String.

public class Hello {

    public static void main(String[] args)
            throws java.io.UnsupportedEncodingException {
        String s = "Hola, señor!";
        System.out.println(s);
        byte[] b = new byte[s.length()];
        for (int i = 0; i < b.length; i++) {
            int cp = s.codePointAt(i);
            b[i] = (byte) cp;
            System.out.print((byte) cp + " ");
        }
        System.out.println();
        System.out.println(new String(b, "UTF-8"));
        System.out.println(new String(b, "US-ASCII"));
        System.out.println(new String(b, "ISO-8859-1"));
    }
}

Output:

Hola, señor!
72 111 108 97 44 32 115 101 -15 111 114 33 
Hola, se�or!
Hola, se�or!
Hola, señor!

user7094 · Accepted Answer · 2010-04-16 15:28:39Z

7

If your string is the output of a password hashing scheme (which it looks like it might be) then I think you will need to Base64 encode in order to put it into plain text.

Standard procedure, if you have raw bytes you want to output to a text file, is to use Base 64 encoding. The Commons Codec library provides a Base64 encoder / decoder for you to use.

Hope this helps.

answered Apr 16, 2010 at 15:28

user7094

3 Comments

Bert F Over a year ago

Recommend the asker create an attribute for that element to indicate the encoding (with a default value in the DTD or schema so you don't necessarily have to specify it in the doc).

Mike B Over a year ago

Yep, it's a hash. I'll have a look at the Commons Codec stuff soon. I assume you just download the jars and implement them into your project?

user7094 Over a year ago

@Ender - yes that's right. There should be a user guide on the site to get you started.

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