implemented resetting passwords

Signed-off-by: Stephan Richter <s.richter@srsoftware.de>

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

@@ -4,12 +4,9 @@ import de.srsoftware.tools.translations.Translation;
 import de.srsoftware.widerhall.data.MailingList;
 import de.srsoftware.widerhall.data.User;
 
-import javax.mail.Message;
 import javax.mail.MessagingException;
 import javax.mail.Multipart;
 import javax.mail.Part;
-import javax.mail.internet.AddressException;
-import javax.mail.internet.InternetAddress;
 import javax.servlet.http.HttpServletRequest;
 import java.io.IOException;
 import java.net.URLEncoder;
@@ -19,6 +16,7 @@ import java.security.NoSuchAlgorithmException;
 import java.sql.ResultSet;
 import java.sql.SQLException;
 import java.util.Map;
+import java.util.Random;
 import java.util.stream.Collectors;
 
 import static de.srsoftware.widerhall.Constants.*;
@@ -28,6 +26,14 @@ public class Util {
     private static final MessageDigest SHA256 = getSha256();
     private static final String EMAIL_PATTERN = "^[a-zA-Z0-9_!#$%&'*+/=?`{|}~^-]+(?:\\.[a-zA-Z0-9_!#$%&'*+/=?`{|}~^-]+)*@[a-zA-Z0-9-]+(?:\\.[a-zA-Z0-9-]+)*$";
 
+    public static char boundedChar(int i) {
+        i = (i<0 ? -i : i) % 62;
+        i += '0';
+        if (i>57) i+=7;
+        if (i>90) i+=6;
+        return (char) i;
+    }
+
     public static String dropEmail(String tx) {
         return tx.replaceAll( "[.\\-\\w]+@[.\\-\\w]+", "[email_removed]");
     }
@@ -119,6 +125,18 @@ public class Util {
         return email.matches(EMAIL_PATTERN);
     }
 
+    public static String randomString(int length) {
+        Random rand = new Random();
+        StringBuilder sb = new StringBuilder();
+        for (int i=0; i<length; i++) {
+            int k = rand.nextInt();
+            char c = boundedChar(k);
+            System.out.println("adding '"+c+"'…");
+            sb.append(c);
+        }
+        return sb.toString();
+    }
+
     public static String sha256(String s) {
         byte[] bytes = SHA256.digest(s.getBytes(StandardCharsets.UTF_8));
         return hex(bytes);