MessageDigest NoSuchAlgorithmException

Question

I want to use MessageDigest to get a MD5 hash, but I get an error.

import java.security.MessageDigest;

public class dn {
  public static void main(         


        

Answer 1

In addition to other answers here

Certain algorithms would not be available with some JVM

To make it truly portable application you should do this

public boolean isMDAvailable(String s)
{
    boolean success=true;
    try{MessageDigest.GetInstance(s);}
    catch(NoSuchAlgorithmException x)
    {
         success=false;
    }
    return success;
}

Now you can get any available MD algorithm with this method

public MessageDigest getAvailableMessageDigest()
{
    if(isMDAvailable("MD5")==true)return MessageDigest.GetInstance("MD5");
    else if(isMDAvailable("MD2")==true)return MessageDigest.GetInstance("MD2");
    else if(isMDAvailable("SHA-512")==true)return MessageDigest.GetInstance("SHA-512");
    else return null;
}

Answer 2

The error message is clear : the code doesn't compile (Unresolved compilation problem) because you're not handling the checked exception NoSuchAlgorithmException that can be thrown by MessageDigest.getInstance().

Either add this exception to the throws clause of the main method, or catch it:

public static void main(String[] args) throws NoSuchAlgorithmException {
    ...
}

or

public static void main(String[] args) {
    try {
        ...
    }
    catch (NoSuchAlgorithmException e) {
        System.err.println("I'm sorry, but MD5 is not a valid message digest algorithm");
    }
}

Note that this is a compilation error. You chose to launch your program despite the presence of compilation errors (visible in the "Problems" view of Eclipse), and despite the fact that Eclipse warned you about that before launching the program. So you tried executing code which doesn't compile, which you shouldn't do.

EDIT: fixed the typo in the code in NoSuchAlgorithmException

Answer 3

You should handle the exception:

try {

   MessageDigest md = MessageDigest.getInstance("MD5");
   //...

} catch(NoSuchAlgorithmException x) {
  // do proper exception handling
}