How to convert byte array to string and vice versa?

user_68274 0
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I have to convert a byte array to string in Android, but my byte array contains negative values.

If I convert that string again to byte array, values I am getting are different from original byte array values.

What can I do to get proper conversion? Code I am using to do the conversion is as follows:

// Code to convert byte arr to str:
byte[] by_original = {0,1,-2,3,-4,-5,6};
String str1 = new String(by_original);
System.out.println("str1 >> "+str1);

// Code to convert str to byte arr:
byte[] by_new = str1.getBytes();
for(int i=0;i<by_new.length;i++) 
System.out.println("by1["+i+"] >> "+str1);

I am stuck in this problem.

java
27 Answers

Even though 

new String(bytes, "UTF-8")

is correct it throws a UnsupportedEncodingException which forces you to deal with a checked exception. You can use as an alternative another constructor since Java 1.6 to convert a byte array into a String:

new String(bytes, StandardCharsets.UTF_8)

This one does not throw any exception.

Converting back should be also done with StandardCharsets.UTF_8:

"test".getBytes(StandardCharsets.UTF_8)

Again you avoid having to deal with checked exceptions.

user_27352860 
  byte[] bytes = "Techie Delight".getBytes();
        // System.out.println(Arrays.toString(bytes));
 
        // Create a string from the byte array without specifying
        // character encoding
        String string = new String(bytes);
        System.out.println(string);
user_51977120

Following is the sample code safely converts byte array to String and String to byte array back.

 byte bytesArray[] = { 1, -2, 4, -5, 10};
 String encoded = java.util.Base64.getEncoder().encodeToString(bytesArray);
 byte[] decoded = java.util.Base64.getDecoder().decode(encoded);
 System.out.println("input: "+Arrays.toString(bytesArray));
 System.out.println("encoded: "+encoded);
 System.out.println("decoded: "+Arrays.toString(decoded));

Output:

input: [1, -2, 4, -5, 10]
encoded: Af4E+wo=
decoded: [1, -2, 4, -5, 10]
user_16546310

I succeeded converting byte array to a string with this method:

public static String byteArrayToString(byte[] data){
    String response = Arrays.toString(data);

    String[] byteValues = response.substring(1, response.length() - 1).split(",");
    byte[] bytes = new byte[byteValues.length];

    for (int i=0, len=bytes.length; i<len; i++) {
        bytes[i] = Byte.parseByte(byteValues[i].trim());
    }

    String str = new String(bytes);
    return str.toLowerCase();
}
user_30602790

This one works for me up to android Q:

You can use the following method to convert o hex string to string

    public static String hexToString(String hex) {
    StringBuilder sb = new StringBuilder();
    char[] hexData = hex.toCharArray();
    for (int count = 0; count < hexData.length - 1; count += 2) {
        int firstDigit = Character.digit(hexData[count], 16);
        int lastDigit = Character.digit(hexData[count + 1], 16);
        int decimal = firstDigit * 16 + lastDigit;
        sb.append((char)decimal);
    }
    return sb.toString();
}

with the following to convert a byte array to a hex string

    public static String bytesToHex(byte[] bytes) {
    char[] hexChars = new char[bytes.length * 2];
    for (int j = 0; j < bytes.length; j++) {
        int v = bytes[j] & 0xFF;
        hexChars[j * 2] = hexArray[v >>> 4];
        hexChars[j * 2 + 1] = hexArray[v & 0x0F];
    }
    return new String(hexChars);
}
user_137941890

Using Kotlin on Android I found out it is handy to create some simple extension functions for that purpose. Solution based on Base64 encoding/decoding to be able to pass via JSON, XML, etc:

import android.util.Base64

fun ByteArray.encodeToString() = String(Base64.encode(this, Base64.NO_WRAP), Charsets.UTF_8)

fun String.decodeToBytes(): ByteArray = Base64.decode(toByteArray(Charsets.UTF_8), Base64.NO_WRAP)

So you can use it

val byteArray = byteArrayOf(0, 1, 2, -1, -2, -3)
val string = byteArray.encodeToString()
val restoredArray = string.decodeToBytes()
user_17384880 
byte[] image = {...};
String imageString = Base64.encodeToString(image, Base64.NO_WRAP);
user_13529190

You can do the following to convert byte array to string and then convert that string to byte array:

// 1. convert byte array to string and then string to byte array

    // convert byte array to string
    byte[] by_original = {0, 1, -2, 3, -4, -5, 6};
    String str1 = Arrays.toString(by_original);
    System.out.println(str1); // output: [0, 1, -2, 3, -4, -5, 6]

    // convert string to byte array
    String newString = str1.substring(1, str1.length()-1);
    String[] stringArray = newString.split(", ");
    byte[] by_new = new byte[stringArray.length];
    for(int i=0; i<stringArray.length; i++) {
        by_new[i] = (byte) Integer.parseInt(stringArray[i]);
    }
    System.out.println(Arrays.toString(by_new)); // output: [0, 1, -2, 3, -4, -5, 6]

But to convert the string to byte array and then convert that byte array to string, below approach can be used:

// 2. convert string to byte array and then byte array to string

    // convert string to byte array
    String str2 = "[0, 1, -2, 3, -4, -5, 6]";
    byte[] byteStr2 = str2.getBytes(StandardCharsets.UTF_8);
    // Now byteStr2 is [91, 48, 44, 32, 49, 44, 32, 45, 50, 44, 32, 51, 44, 32, 45, 52, 44, 32, 45, 53, 44, 32, 54, 93]

    // convert byte array to string
    System.out.println(new String(byteStr2, StandardCharsets.UTF_8)); // output: [0, 1, -2, 3, -4, -5, 6]
user_173642720
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