Arrays equals return false for same byte arrays

Question

First I create a signature (byte[] signature). Then I write this signature to the file. I read the signature from this file and give it another variable (byte [] signatureCopy). But when I compare these two variables, it returns false. How can I resolve it?

But when I print the screen, it looks the same.

System.out.println (new String (signature));
System.out.println (new String (signatureCopy));

Code:

    byte[] signature = this.signature(data);        
    FileUtil.writeRegistryFileSigned(path, signature);
    byte[] signatureCopy = FileUtil.readSignatureInRegistryFile(path);
    System.out.println(Arrays.equals(signature, signatureCopy)); //FALSE

Functions;

public static byte[] readSignatureInRegistryFile(String filePath){
    byte[] data = null;
    try {
        data = Files.readAllBytes(Paths.get(filePath));
    } catch (IOException e) {
        e.printStackTrace();
    }
    return data;        
}


public static void writeRegistryFileSigned(String filePath, byte[] signature) {
    File fileRegistry = new File(filePath);
    try {
        fileRegistry.createNewFile();
    } catch (IOException e1) {

    }
    try (FileWriter fw = new FileWriter(fileRegistry, true);
            BufferedWriter bw = new BufferedWriter(fw);
            PrintWriter out = new PrintWriter(bw)) {            
        out.println(new String(signature));

    } catch (IOException e) {
    }

}

Don't use a Writer to write binary data. use an OutputStream. new String(signature) is a lossy operation that doesn't make sense (since the byte array does NOT represent characters encoded using your default charset), and println() adds EOL character(s). — JB Nizet
– JB Nizet, Commented Oct 28, 2017 at 18:48
Thank you. OutputStream worked. Why does not Writer work, OutputStream works. Can you explain? — cezaalp
– cezaalp, Commented Oct 29, 2017 at 12:39

laune · Accepted Answer · 2017-10-28 18:49:45Z

5

You are writing using println which will add a CR-LF or LF to the String.

readAllBytes will really read all bytes, including the CR-LF or LF.

Therefore, the arrays differ, although the printed strings look the same. (Although, you should notice the extra line feed.)

Moreover: If you convert bytes to a String, some encoding is in effect and this may or may not produce what you want. If your signature is supposed to be a byte array, don't convert it to String for printing, rather print the byte values as numeric values, in hexadecimal.

answered Oct 28, 2017 at 18:49

laune

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1 Comment

Razib Over a year ago

nicely explained. I was also wondering why its not printing 'true'.

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