added tests, overhauled implementation of Util.hex

src/main/java/de/srsoftware/widerhall/Util.java

@@ -1,16 +1,12 @@
 package de.srsoftware.widerhall;
 
-import de.srsoftware.examples.translations.App;
 import de.srsoftware.tools.translations.Translation;
 
 import java.net.URLEncoder;
 import java.nio.charset.StandardCharsets;
 import java.security.MessageDigest;
 import java.security.NoSuchAlgorithmException;
-import java.util.Arrays;
-import java.util.List;
 import java.util.Map;
-import java.util.regex.Pattern;
 import java.util.stream.Collectors;
 
 public class Util {
@@ -51,8 +47,10 @@ public class Util {
         return buf.toString();
     }
 
-    private static String hex(byte b){
-        return (b<16 ? "0" : "") + Integer.toHexString(b);
+    public static String hex(int b){
+        int lower = b & 0x0F;
+        int upper = (b & 0xF0) >> 4;
+        return (char)(upper < 10 ? '0'+upper : 'A'+upper-10)+""+(char)(lower < 10 ? '0'+lower : 'A'+lower-10);
     }
 
     public static String t(String tx, Object ... fills){