MD5Checksum.java

import java.io.*;
import java.security.MessageDigest;

public class MD5Checksum {

  public static byte[] createChecksum(String filename) throws Exception
  {
    InputStream fis =  new FileInputStream(filename);

    byte[] buffer = new byte[1024];
    MessageDigest complete = MessageDigest.getInstance("MD5");
    int numRead;
    do {
      numRead = fis.read(buffer);
      if (numRead > 0) {
        complete.update(buffer, 0, numRead);
      }
    } while (numRead != -1);
    fis.close();
    return complete.digest();
  }

  // see this How-to for a faster way to convert
  // a byte array to a HEX string
  public static String getMD5Checksum(String filename) throws Exception {
    byte[] b = createChecksum(filename);
    String result = "";
    for (int i=0; i < b.length; i++) {
      result +=
	Integer.toString( ( b[i] & 0xff ) + 0x100, 16).substring( 1 );
    }
    return result;
  }

  // public static void main(String args[]) {
  //   try {
  //     System.out.println(getMD5Checksum("apache-tomcat-5.5.17.exe"));
  //   }
  //   catch (Exception e) {
  //     e.printStackTrace();
  //   }
  // }
}