How to convert a Binary String to UTF-8 String in java?

Question

i am doing a project which requires me to convert UTF-8 string stored in a windows text file into a continuous binary string and store it in a windows text file. and then read this binary string and convert it back to the original UTF-8 String and store it in a text file. i converted the UTF-8 string to Binarystring but have no idea how to reverse the process.

here's my program to convert UTF-8 String to Binary strings.

package filetobits;

import java.io.FileNotFoundException;
import java.io.FileReader;
import java.io.FileWriter;
import java.io.IOException;

public class FileToBits {

    public static void main(String[] args) throws IOException, FileNotFoundException {

        FileReader inputStream = new FileReader("C:\\FileTesting\\UTF8.txt");
        FileWriter outputStream = new FileWriter("C:\\FileTesting\\BinaryStrings.txt");

        int c;

        while ((c = inputStream.read()) != -1) {

            outputStream.write(Integer.toBinaryString(c));
            outputStream.write(System.lineSeparator());
        }
        inputStream.close();
        outputStream.close();
    }
}

here's my input(16 characters):

¼¹¨'I.p

here's my output:

1111111111111101 10000 1111111111111101 11111 1111111111111101 100111 1001001 101110 1110000 111100 1111111111111101 1100001 101100 101001 1111111111111101 1111111111111101

i need help converting these binary strings back to a single UTF-8 String and store it in a text file.

i achieved what i want with the following code:

    String str = "";
    FileReader inputStream = new FileReader("C:\\FileTesting\\Encrypted.txt");
    FileWriter outputStream = new FileWriter("C:\\FileTesting\\EncryptedBin.txt");
int c;
while ((c  = inputStream.read()) != -1) {
String s = String.format("%16s", Integer.toBinaryString(c)).replace(' ', '0');
for (int i = 0; i < s.length() / 16; i++) {
int a = Integer.parseInt(s.substring(16 * i, (i + 1) * 16), 2);
str += (char) (a);
    }
   }

But the problem is i cant add extra 0's to make every binary string to a length of 16, because i need to store this data in a image(for my image steganography project). so the shorter the binary string the better.

i need to get the same output produced by the above code but without converting every binary string to a length of 16.

PS: i am kinda lost when it comes to character encodings. is storing UTF-8 characters in a windows txt file convert them to ANSI or something?

I think this is what you needed docs.oracle.com/javase/7/docs/api/java/lang/… and in reverse process you can simply create a new String instance from bytes. — eatSleepCode
– eatSleepCode, Commented Jan 28, 2017 at 12:43
Possible duplicate of How to parse String as Binary and convert it to UTF-8 equivalent in Java? — Sabir Khan
– Sabir Khan, Commented Jan 28, 2017 at 12:45
@SabirKhan i'm sorry but it's not a duplicate, i can't afford to write extra bits to make every character 16 bits binary value. — NoobScript
– NoobScript, Commented Jan 28, 2017 at 12:51
Exactly where did you see that UTF-8 requires 16 bits per character? The number of bytes required per character varies and depending what these byte values are, the decoder knows how many bytes to read to recreate a character. By the way, are you ACTUALLY required to write the binary string of your UTF-8 string to a file, or is this an intermediate step of your own to make sure the conversion is correct before you embed the bits to your image? Because in that case, you don't even need a bit string, just the bytes array. — Reti43
– Reti43, Commented Jan 28, 2017 at 13:04
@Reti43 you're right. i don't need to convert it into binary string. i just don't know how to embed these bytes directly into LSB's of pixels. so i thought it would be easier to first convert it into a string of 0's and 1's then embed bit by bit. — NoobScript
– NoobScript, Commented Jan 28, 2017 at 13:09

Christoph Bimminger · Accepted Answer · 2017-01-28 12:43:58Z

0

a byte has 8 bits. in a first step, ignore the UTF-8 issue, just fill a byte[] with the data from your binary string.

When you have a byte[] data, you can use new String(d) to create an UTF-8 String (Java Strings are UTF-8 be default).

answered Jan 28, 2017 at 12:43

Christoph Bimminger

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3 Comments

Christoph Bimminger Over a year ago

btw - when writing a file in java, it's by default UTF-8. You can specify alternative output by using a charset when opening the FileOutputStream or whatelse (Charset.forName("iso-8859-1") or sth like this)

NoobScript Over a year ago

but doesn't the UTF-8 String contain 16bit charcters? how can i store it in a byte(8-bits) array?

Christoph Bimminger Over a year ago

UTF-8 may store characters as 1-byte, 2-byte, and even up to 4-byte sequences. The 1-byte charset is compatible with 7bit ASCII. There are differences only in the 8bit ASCII (so ASCII 128..256). When storing a 1 byte UTF-8 char in a byte[] it will use only one element of the array. When storing a multibyte char in a byte[] you will see that several bytes of the byte[] are used to store this single character.

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