Consider a following code snippet
byte[] b = new byte[]{ 0, 0, 0, -127 }; // possible Byte Array
// converted byte array to String using UTF-8
String s = String(b, StandardCharsets.UTF_8);
Now try again to convert the string into byte array
b = s.getBytes(StandardCharsets.UTF_8);
now when we compare it with original byte array, the value is not same on round trip
[0, 0, 0, -17, -65, -67]
Can anyone suggest how can we convert back the string to original byte array
The most stable answer is that you should go between a byte array and a hex string which is 1 byte == 2 character between 0 and F in a UTF-8 format.
Then convert back from hex to byte array To other stack trace questions for how to go to them.
Byte to hex: How to convert a byte array to a hex string in Java?
Hex to byte: Convert a string representation of a hex dump to a byte array using Java?
Although I cannot understand the reason why you need a not valid UTF-8 string, I have an explaining solution for you (paste this code into your TestDrive class (a runnable class containing static void main(String[] args) function:
public static void main(String[] args) {
byte[] bytes1 = new byte[]{0, 0, 0, -127};
int[] unsigned = toUnsignedInt(bytes1);
String utf8String = toUtf8String(unsigned);
char[] chars = utf8String.toCharArray();
byte[] bytes2 = toBytes(chars);
System.out.println(Arrays.equals(bytes1, bytes2));
}
private static int[] toSigned(byte[] unsigned) {
int[] signed = new int[unsigned.length];
for (int i = 0; i < unsigned.length; i++) {
signed[i] = 2;
}
return signed;
}
private static int[] toUnsignedInt(byte[] signed) {
int[] unsigned = new int[signed.length];
for (int i = 0; i < signed.length; i++) {
unsigned[i] = Byte.toUnsignedInt(signed[i]);
}
return unsigned;
}
private static String toUtf8String(int[] unsigned) {
char[] chars = toChars(unsigned);
return new String(chars);
}
private static char[] toChars(int[] unsigned) {
char[] chars = new char[unsigned.length];
for (int i = 0; i < unsigned.length; i++) {
chars[i] = (char) unsigned[i];
}
return chars;
}
private static byte[] toBytes(char[] chars) {
int[] unsigned = toUnsignedInt(chars);
byte[] bytes = new byte[unsigned.length];
for (int i = 0; i < unsigned.length; i++) {
bytes[i] = (byte) unsigned[i];
}
return bytes;
}
private static int[] toUnsignedInt(char[] chars) {
int[] unsigned = new int[chars.length];
for (int i = 0; i < chars.length; i++) {
unsigned[i] = (int) chars[i];
}
return unsigned;
}
The most stable answer is to leave the byte array alone and pass it around, and avoid the String and round-trip completely. String is not a container for binary data.
