I don't know how to acquire token without username and password using the adal4j library. I have this code:

```
public class GetToken implements AuthenticationCallback {

    public static void main(String[] args) {
        // TODO Auto-generated method stub
        String resource = "resource";
        String redirectUrl = "redirecturl";
        String authority = "https://login.microsoftonline.com/common/";
        ExecutorService executor = null;
        ClientAssertion clientId = new ClientAssertion("my-client-id");
        AuthenticationCallback callback;
        // Authenticate the registered application with Azure Active Directory.
        AuthenticationContext authContext;
        try {
            authContext = new AuthenticationContext(authority, false,executor);
        } catch (MalformedURLException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
        Future <AuthenticationResult> result = authContext.acquireToken(resource, clientId, callback);
    }

    @Override
    public void onSuccess(AuthenticationResult result) {
        // TODO Auto-generated method stub

    }

    @Override
    public void onFailure(Throwable exc) {
        // TODO Auto-generated method stub

    }

}

```

And I don't know how to acquire token ....