How to convert byte array to string and vice versa?

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.

Your byte array must have some encoding. The encoding cannot be ASCII if you've got negative values. Once you figure that out, you can convert a set of bytes to a String using:

byte[] bytes = {...}
String str = new String(bytes, StandardCharsets.UTF_8); // for UTF-8 encoding

There are a bunch of encodings you can use, look at the supported encodings in the Oracle javadocs.

The "proper conversion" between byte[] and String is to explicitly state the encoding you want to use. If you start with a byte[] and it does not in fact contain text data, there is no "proper conversion". Strings are for text, byte[] is for binary data, and the only really sensible thing to do is to avoid converting between them unless you absolutely have to.

If you really must use a String to hold binary data then the safest way is to use Base64 encoding.

The root problem is (I think) that you are unwittingly using a character set for which:

 bytes != encode(decode(bytes))

in some cases. UTF-8 is an example of such a character set. Specifically, certain sequences of bytes are not valid encodings in UTF-8. If the UTF-8 decoder encounters one of these sequences, it is liable to discard the offending bytes or decode them as the Unicode codepoint for "no such character". Naturally, when you then try to encode the characters as bytes the result will be different.

The solution is:

1. Be explicit about the character encoding you are using; i.e. use a String constructor and String.toByteArray method with an explicit charset.
2. Use the right character set for your byte data ... or alternatively one (such as "Latin-1" where all byte sequences map to valid Unicode characters.
3. If your bytes are (really) binary data and you want to be able to transmit / receive them over a "text based" channel, use something like Base64 encoding ... which is designed for this purpose.

---

For Java, the most common character sets are in java.nio.charset.StandardCharsets. If you are encoding a string that can contain any Unicode character value then UTF-8 encoding (UTF_8) is recommended.

If you want a 1:1 mapping in Java then you can use ISO Latin Alphabet No. 1 - more commonly just called "Latin 1" or simply "Latin" (ISO_8859_1). Note that Latin-1 in Java is the IANA version of Latin-1 which assigns characters to all possible 256 values including control blocks C0 and C1. These are not printable: you won't see them in any output.

From Java 8 onwards Java contains java.util.Base64 for Base64 encoding / decoding. For URL-safe encoding you may want to to use Base64.getUrlEncoder instead of the standard encoder. This class is also present in Android since Android Oreo (8), API level 26.

We just need to construct a new String with the array: http://www.mkyong.com/java/how-do-convert-byte-array-to-string-in-java/

String s = new String(bytes);

The bytes of the resulting string differs depending on what charset you use. new String(bytes) and new String(bytes, Charset.forName("utf-8")) and new String(bytes, Charset.forName("utf-16")) will all have different byte arrays when you call String#getBytes() (depending on the default charset)

Using new String(byOriginal) and converting back to byte[] using getBytes() doesn't guarantee two byte[] with equal values. This is due to a call to StringCoding.encode(..) which will encode the String to Charset.defaultCharset(). During this encoding, the encoder might choose to replace unknown characters and do other changes. Hence, using String.getBytes() might not return an equal array as you've originally passed to the constructor.

Why was the problem: As someone already specified: If you start with a byte[] and it does not in fact contain text data, there is no "proper conversion". Strings are for text, byte[] is for binary data, and the only really sensible thing to do is to avoid converting between them unless you absolutely have to.

I was observing this problem when I was trying to create byte[] from a pdf file and then converting it to String and then taking the String as input and converting back to file.

So make sure your encoding and decoding logic is same as I did. I explicitly encoded the byte[] to Base64 and decoded it to create the file again.

Use-case: Due to some limitation I was trying to sent byte[] in request(POST) and the process was as follows:

PDF File >> Base64.encodeBase64(byte[]) >> String >> Send in request(POST) >> receive String >> Base64.decodeBase64(byte[]) >> create binary

Try this and this worked for me..

File file = new File("filePath");

		byte[] byteArray = new byte[(int) file.length()];

		try {
			FileInputStream fileInputStream = new FileInputStream(file);
			fileInputStream.read(byteArray);
			
			String byteArrayStr= new String(Base64.encodeBase64(byteArray));

			FileOutputStream fos = new FileOutputStream("newFilePath");
			fos.write(Base64.decodeBase64(byteArrayStr.getBytes()));
			fos.close();
		} 
		catch (FileNotFoundException e) {
			System.out.println("File Not Found.");
			e.printStackTrace();
		}
		catch (IOException e1) {
			System.out.println("Error Reading The File.");
			e1.printStackTrace();
		}

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.

private static String toHexadecimal(byte[] digest){
        String hash = "";
    for(byte aux : digest) {
        int b = aux & 0xff;
        if (Integer.toHexString(b).length() == 1) hash += "0";
        hash += Integer.toHexString(b);
    }
    return hash;
}

This works fine for me:

String cd = "Holding some value";

Converting from string to byte[]:

byte[] cookie = new sun.misc.BASE64Decoder().decodeBuffer(cd);

Converting from byte[] to string:

cd = new sun.misc.BASE64Encoder().encode(cookie);

I did notice something that is not in any of the answers. You can cast each of the bytes in the byte array to characters, and put them in a char array. Then the string is

new String(cbuf)

where cbuf is the char array. To convert back, loop through the string casting each of the chars to bytes to put into a byte array, and this byte array will be the same as the first.

public class StringByteArrTest {



public static void main(String[] args) {
	// put whatever byte array here
	byte[] arr = new byte[] {-12, -100, -49, 100, -63, 0, -90};
	for (byte b: arr) System.out.println(b);
	// put data into this char array
	char[] cbuf = new char[arr.length];
	for (int i = 0; i < arr.length; i++) {
		cbuf[i] = (char) arr[i];
	}
	// this is the string
	String s = new String(cbuf);
	System.out.println(s);

	// converting back
	byte[] out = new byte[s.length()];
	for (int i = 0; i < s.length(); i++) {
		out[i] = (byte) s.charAt(i);
	}
	for (byte b: out) System.out.println(b);
}




}

javax.xml.bind.DatatypeConverter should do it:

byte [] b = javax.xml.bind.DatatypeConverter.parseHexBinary("E62DB");
String s = javax.xml.bind.DatatypeConverter.printHexBinary(b);

Heres a few methods that convert an array of bytes to a string. I've tested them they work well.

public String getStringFromByteArray(byte[] settingsData) {

	ByteArrayInputStream byteArrayInputStream = new ByteArrayInputStream(settingsData);
	Reader reader = new BufferedReader(new InputStreamReader(byteArrayInputStream));
	StringBuilder sb = new StringBuilder();
	int byteChar;

	try {
		while((byteChar = reader.read()) != -1) {
			sb.append((char) byteChar);
		}
	}
	catch(IOException e) {
		e.printStackTrace();
	}

	return sb.toString();

}

public String getStringFromByteArray(byte[] settingsData) {

	StringBuilder sb = new StringBuilder();
	for(byte willBeChar: settingsData) {
		sb.append((char) willBeChar);
	}
	
	return sb.toString();

}

While base64 encoding is safe and one could argue "the right answer", I arrived here looking for a way to convert a Java byte array to/from a Java String as-is. That is, where each member of the byte array remains intact in its String counterpart, with no extra space required for encoding/transport.

This answer describing 8bit transparent encodings was very helpful for me. I used ISO-8859-1 on terabytes of binary data to convert back and forth successfully (binary <-> String) without the inflated space requirements needed for a base64 encoding, so is safe for my use-case - YMMV.

This was also helpful in explaining when/if you should experiment.

import sun.misc.BASE64Decoder;
import sun.misc.BASE64Encoder;    

private static String base64Encode(byte[] bytes)
{
    return new BASE64Encoder().encode(bytes);
}

private static byte[] base64Decode(String s) throws IOException
{
    return new BASE64Decoder().decodeBuffer(s);
}

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();
}

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);
}

  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);

Here the working code.

            // Encode byte array into string . TemplateBuffer1 is my bytearry variable.
        
        String finger_buffer = Base64.encodeToString(templateBuffer1, Base64.DEFAULT);
        Log.d(TAG, "Captured biometric device->" + finger_buffer);
        
        
        // Decode String into Byte Array. decodedString is my bytearray[] 
        decodedString = Base64.decode(finger_buffer, Base64.DEFAULT);

You can use simple for loop for conversion:

public void byteArrToString(){
   byte[] b = {'a','b','$'};
   String str = ""; 
   for(int i=0; i<b.length; i++){
	   char c = (char) b[i];
	   str+=c;
   }
   System.out.println(str);
}

byte[] image = {...};
String imageString = Base64.encodeToString(image, Base64.NO_WRAP);

Try to specify an 8-bit charset in both conversions. ISO-8859-1 for instance.

Read the bytes from String using ByteArrayInputStream and wrap it with BufferedReader which is Char Stream instead of Byte Stream which converts the byte data to String.

package com.cs.sajal;

import java.io.BufferedReader;
import java.io.ByteArrayInputStream;
import java.io.InputStreamReader;
import java.io.UnsupportedEncodingException;

public class TestCls {

	public static void main(String[] args) {

		String s=new String("Sajal is  a good boy");

	    try
	    {
	    ByteArrayInputStream bis;
	    bis=new ByteArrayInputStream(s.getBytes("UTF-8"));

	    BufferedReader br=new BufferedReader(new InputStreamReader(bis));
	    System.out.println(br.readLine());

	    }
	    catch(Exception e)
	    {
		    e.printStackTrace();
	    }

    }
}

Output is: >Sajal is a good boy

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]

A string is a collection of char's (16bit unsigned). So if you are going to convert negative numbers into a string, they'll be lost in translation.

public class byteString {

	/**
	 * @param args
	 */
	public static void main(String[] args) throws Exception {
		// TODO Auto-generated method stub
		String msg = "Hello";
		byte[] buff = new byte[1024];
		buff = msg.getBytes("UTF-8");
		System.out.println(buff);
		String m = new String(buff);
		System.out.println(m);
		

	}

}