import java.io.IOException;
import java.net.HttpURLConnection;

import org.springframework.ws.transport.http.HttpUrlConnectionMessageSender;

import sun.misc.BASE64Encoder;

public class CustomWSMessageSender extends HttpUrlConnectionMessageSender{

    @Override
    protected void prepareConnection(HttpURLConnection connection)
            throws IOException {
        
        BASE64Encoder enc = new sun.misc.BASE64Encoder();
        String userpassword = "yourUser:yourPassword";
        String encodedAuthorization = enc.encode( userpassword.getBytes() );
        connection.setRequestProperty("Authorization", "Basic " + encodedAuthorization);

        super.prepareConnection(connection);
    }
}

myWSClient.setMessageSender(new CustomWSMessageSender());