Pure Java implementation of MD5 Algorithm

Pure Java implementation of MD5 Algorithm

  September 04, 2022    Nikos Siatras

---

The following Java algorithm generates MD5 hashes from String, Byte array and File.

import java.io.File;
import java.io.FileInputStream;
import java.io.IOException;
import java.security.MessageDigest;
import java.security.NoSuchAlgorithmException;

/**
 *
 * @author Nikos Siatras
 */
public class MD5
{

    public MD5()
    {

    }

    /**
     * Return the MD5 string representation of the given string
     *
     * @param str is the string to get the MD5
     * @return
     * @throws NoSuchAlgorithmException
     */
    public String getMD5FromString(String str) throws NoSuchAlgorithmException
    {
        MessageDigest md = MessageDigest.getInstance("MD5");
        byte[] array = md.digest(str.getBytes());
        StringBuilder sb = new StringBuilder();
        for (int i = 0; i < array.length; ++i)
        {
            sb.append(Integer.toHexString((array[i] & 0xFF) | 0x100).substring(1, 3));
        }
        return sb.toString().toUpperCase();
    }

    /**
     * Return the MD5 string representation of the given byte array
     *
     * @param bytes is the byte array to get the MD5
     * @return
     * @throws NoSuchAlgorithmException
     */
    public String getMD5FromByteArray(byte[] bytes) throws NoSuchAlgorithmException
    {
        MessageDigest md = MessageDigest.getInstance("MD5");
        byte[] array = md.digest(bytes);
        StringBuilder sb = new StringBuilder();
        for (int i = 0; i < array.length; ++i)
        {
            sb.append(Integer.toHexString((array[i] & 0xFF) | 0x100).substring(1, 3));
        }
        return sb.toString().toUpperCase();
    }

    /**
     * Return the MD5 string representation of the given file
     *
     * @param file is the file to get the MD5
     * @return
     * @throws NoSuchAlgorithmException
     * @throws IOException
     */
    public String getMD5FromFile(File file) throws NoSuchAlgorithmException, IOException
    {
        MessageDigest md = MessageDigest.getInstance("MD5"); // SHA or MD5
        String hash = "";

        byte[] data = new byte[(int) file.length()];
        FileInputStream fis = new FileInputStream(file);
        fis.read(data);
        fis.close();

        // Reads it all at one go. Might be better to chunk it.
        md.update(data);

        byte[] digest = md.digest();

        for (int i = 0; i < digest.length; i++)
        {
            String hex = Integer.toHexString(digest[i]);
            if (hex.length() == 1)
            {
                hex = "0" + hex;
            }
            hex = hex.substring(hex.length() - 2);
            hash += hex;
        }

        return hash.toUpperCase();
    }
}