Converting byte array to String (Java)

I'm writing a web application in Google app Engine. It allows people to basically edit html code that gets stored as an .html file in the blobstore.

I'm using fetchData to return a byte[] of all the characters in the file. I'm trying to print to an html in order for the user to edit the html code. Everything works great!</p> <p>Here's my only problem now:</p> <p>The byte array is having some issues when converting back to a string. Smart quotes and a couple of characters are coming out looking funky. (?'s or japanese symbols etc.) Specifically it's several bytes I'm seeing that have negative values which are causing the problem.</p> <p>The smart quotes are coming back as <code>-108</code> and <code>-109</code> in the byte array. Why is this and how can I decode the negative bytes to show the correct character encoding?</p>

The byte array contains characters in a special encoding (that you should know). The way to convert it to a String is:

String decoded = new String(bytes, "UTF-8");  // example for one encoding type

By The Way - the raw bytes appear may appear as negative decimals just because the java datatype byte is signed, it covers the range from -128 to 127.

---

-109 = 0x93: Control Code "Set Transmit State"

The value (-109) is a non-printable control character in UNICODE. So UTF-8 is not the correct encoding for that character stream.

0x93 in "Windows-1252" is the "smart quote" that you're looking for, so the Java name of that encoding is "Cp1252". The next line provides a test code:

System.out.println(new String(new byte[]{-109}, "Cp1252")); 

Java 7 and above

You can also pass your desired encoding to the String constructor as a Charset constant from StandardCharsets. This may be safer than passing the encoding as a String, as suggested in the other answers.

For example, for UTF-8 encoding

String bytesAsString = new String(bytes, StandardCharsets.UTF_8);

You can try this.

String s = new String(bytearray);

public class Main {
    
    /**
     * Example method for converting a byte to a String.
     */
    public void convertByteToString() {
        
        byte b = 65;
        
        //Using the static toString method of the Byte class
        System.out.println(Byte.toString(b));

        //Using simple concatenation with an empty String
        System.out.println(b + "");
        
        //Creating a byte array and passing it to the String constructor
        System.out.println(new String(new byte[] {b}));
        
    }
    
    /**
     * @param args the command line arguments
     */
    public static void main(String[] args) {
        new Main().convertByteToString();
    }
}

Output

65
65
A

public static String readFile(String fn)   throws IOException 
{
	File f = new File(fn);
	
	byte[] buffer = new byte[(int)f.length()];
	FileInputStream is = new FileInputStream(fn);
	is.read(buffer);
	is.close();
	
	return  new String(buffer, "UTF-8"); // use desired encoding
}

I suggest Arrays.toString(byte_array);

It depends on your purpose. For example, I wanted to save a byte array exactly like the format you can see at time of debug that is something like this : [1, 2, 3] If you want to save exactly same value without converting the bytes to character format, Arrays.toString (byte_array) does this,. But if you want to save characters instead of bytes, you should use String s = new String(byte_array). In this case, s is equal to equivalent of [1, 2, 3] in format of character.

The previous answer from Andreas_D is good. I'm just going to add that wherever you are displaying the output there will be a font and a character encoding and it may not support some characters.

To work out whether it is Java or your display that is a problem, do this:

    for(int i=0;i<str.length();i++) {
        char ch = str.charAt(i);
        System.out.println(i+" : "+ch+" "+Integer.toHexString(ch)+((ch=='\ufffd') ? " Unknown character" : ""));
    }

Java will have mapped any characters it cannot understand to 0xfffd the official character for unknown characters. If you see a '?' in the output, but it is not mapped to 0xfffd, it is your display font or encoding that is the problem, not Java.