md5 hash function
md5 is a cryptographic hash funtion. the input is a some data, a text string or whatever. the output is a fixed length byte array. it is impossible to reconstruct the original data from the output data. if the input gets changed just a tiny bit the output is completely different.
java supports multible hash algorithms, one of the not so secure but often used is md5. to create an md5 hash of a string you need about following code:
import java.security.MessageDigest;
....
// here we store the output as a hex encoded string
StringBuilder builder = new StringBuilder();
MessageDigest md5 = MessageDigest.getInstance("MD5");
// we use the string "HELLO" as input
md5.update("HELLO".getBytes());
// now we have to iterate over the output bytearray
for (byte b : md5.digest()) {
// make an int out of the byte. the
// & 0xff is to remove the sign bit
int i = b & 0xff;
if (i < 0x10) { // if it's less than 16, add a 0 for padding
builder.append("0");
}
builder.append(Integer.toHexString(i));
}
// print the finished hex string
System.out.println(builder.toString());
the output should be eb61eead90e3b899c6bcbe27ac581660
if you need only a single hash you can use an online hash calculator. this one supports not only md5, he also supports older, less secure algorithms and newer more secure algorithms.