A quick little utility to generate SHA-256 file hashes.

Main.java

package io.sjm.hash;

import java.io.BufferedInputStream;
import java.io.BufferedWriter;
import java.io.File;
import java.io.FileInputStream;
import java.io.FileWriter;
import java.io.IOException;
import java.io.InputStream;
import java.math.BigInteger;
import java.security.MessageDigest;
import java.util.Arrays;

public class Main {
  public static String calc(InputStream is) {
    String output;
    int read;
    byte[] buffer = new byte[8192];

    try {
      MessageDigest digest = MessageDigest.getInstance("SHA-256");
      while ((read = is.read(buffer)) > 0) {
        digest.update(buffer, 0, read);
      }
      byte[] hash = digest.digest();
      BigInteger bigInt = new BigInteger(1, hash);
      output = bigInt.toString(16);
      while (output.length() < 64) {
        output = "0" + output;
      }
    } catch (Exception e) {
      e.printStackTrace();
      return null;
    }

    return output;
  }

  public static String calcFile(String filename) {
    String format = "SHA256 (%s) = %s";
    File f = new File(filename);
    try (BufferedInputStream bis = new BufferedInputStream(new FileInputStream(f))) {
      return String.format(format, f.getName(), calc(bis));
    } catch (IOException e) {
      System.err.println(e.getClass() + ": " + e.getMessage());
    }

    return null;
  }

  public static void main(String[] args) {
    String[] opts = args.clone();

    if (opts.length == 0) {
      System.err.println("usage: hash.jar [-w] <filename>\n");
      System.err.println("-w:\twrite the output to \"SHA256\"");
      System.exit(-1);
    }

    boolean writeFile = false;
    if (opts[0].equals("-w")) {
      File f = new File("SHA256");
      if (f.exists()) {
        System.err.println("File " + f.getName() + " already exists.");
        System.exit(-1);
      }

      writeFile = true;
      opts = Arrays.copyOfRange(opts, 1, opts.length);
    }

    StringBuffer sb = new StringBuffer();
    Arrays.stream(opts).forEach(opt -> sb.append(calcFile(opt) + "\n"));
    if (writeFile) {
      File f = new File("SHA256");
      try (BufferedWriter bw = new BufferedWriter(new FileWriter(f))) {
        bw.write(sb.toString());
      } catch (IOException e) {
        e.printStackTrace();
      }
    } else {
      System.out.print(sb);
    }

    System.exit(0);
  }
}