implement sha1 hash generation

src/main/java/PasswordValidator.java

@@ -1,3 +1,6 @@
+import java.math.BigInteger;
+import java.security.MessageDigest;
+import java.security.NoSuchAlgorithmException;
 import java.util.regex.Pattern;
 
 public class PasswordValidator {
@@ -54,4 +57,30 @@ public class PasswordValidator {
     public void setRequireDigit(boolean requireDigit) {
         this.requireDigit = requireDigit;
     }
+
+    public static String getSHA1Hash(String input) {
+        if (input.length() > 0) {
+            try {
+                MessageDigest md = MessageDigest.getInstance("SHA-1");
+                byte[] messageDigest = md.digest(input.getBytes());
+
+                // Convert byte array into signum representation
+                BigInteger no = new BigInteger(1, messageDigest);
+
+                // Convert message digest into hex value
+                StringBuilder hashtext = new StringBuilder();
+                hashtext.append(no.toString(16));
+
+                // Add preceding 0s to make it 32 bit
+                while (hashtext.length() < 32) {
+                    hashtext.insert(0, "0");
+                }
+                return hashtext.toString();
+            } catch (NoSuchAlgorithmException e) {
+                e.printStackTrace();
+            }
+        }
+
+        return null;
+    }
 }

src/test/java/PasswordValidatorTest.java

@@ -47,4 +47,11 @@ class PasswordValidatorTest {
         assertFalse(passwordValidator.validate("ABCDEF8"));
         assertTrue(passwordValidator.validate("abCDE8F"));
     }
+
+    @Test
+    void getSHA1Hash() {
+        assertEquals("356A192B7913B04C54574D18C28D46E6395428AB".toLowerCase(), PasswordValidator.getSHA1Hash("1"));
+        assertEquals("A233F0E898ED0661D6D47ED0958F16B52E537231".toLowerCase(), PasswordValidator.getSHA1Hash("asdf12"));
+        assertNull(PasswordValidator.getSHA1Hash(""));
+    }
 }