added Luhn algorithm / validator

security/src/main/java/de/muehlencord/shared/security/Luhn.java

@@ -0,0 +1,61 @@
+/*
+ * File: $$RCSfile$$
+ *
+ * Copyright (c) 2011 by Wincor Nixdorf,
+ * Heinz-Nixdorf-Ring 1, 33106 Paderborn, Germany
+ *
+ * This software is the confidential and proprietary information
+ * of Wincor Nixdorf.
+ *
+ * You shall not disclose such confidential information and shall
+ * use it only in accordance with the terms of the license agreement
+ * you entered into with Wincor Nixdorf.
+ */
+package de.muehlencord.shared.security;
+
+/**
+ *
+ * @author joern.muehlencord
+ */
+public class Luhn {
+
+    public static boolean validateNumber(final String numberStr) {
+        return (computeCheckDigit(numberStr, true) == 0);
+    }
+
+    public static int computeCheckDigit(final String numberStr, final boolean isCheckDigitAttached) {
+        boolean doubleNextDigit = !isCheckDigitAttached;
+        int sum = 0;
+
+        // iterate from right digit to left
+        for (int currentDigitPos = numberStr.length() - 1; currentDigitPos >= 0; currentDigitPos--) {
+            int currentDigit = Integer.parseInt(String.valueOf(numberStr.charAt(currentDigitPos)));
+            if (doubleNextDigit) {
+                currentDigit = currentDigit * 2;
+            }
+            sum += singleDigitSum(currentDigit);
+            doubleNextDigit = !doubleNextDigit;
+        }
+
+        if ((sum % 10) > 0) {
+            return (10 - (sum % 10));
+        } else {
+            return 0;
+        }
+    }
+
+    private static int singleDigitSum(final int value) {
+        if (value < 10) {
+            return value;
+        } else {
+            return singleDigitSum((value / 10) + (value % 10));
+        }
+    }
+}
+
+/**
+ * History:
+ *
+ * $$Log$$
+ *
+ */

security/src/test/java/de/muehlencord/shared/security/LuhnTest.java

@@ -0,0 +1,57 @@
+/*
+ * File: $$RCSfile$$
+ *
+ * Copyright (c) 2011 by Wincor Nixdorf,
+ * Heinz-Nixdorf-Ring 1, 33106 Paderborn, Germany
+ *
+ * This software is the confidential and proprietary information
+ * of Wincor Nixdorf.
+ *
+ * You shall not disclose such confidential information and shall
+ * use it only in accordance with the terms of the license agreement
+ * you entered into with Wincor Nixdorf.
+ */
+package de.muehlencord.shared.security;
+
+import org.junit.Test;
+import static org.junit.Assert.*;
+
+/**
+ *
+ * @author joern.muehlencord
+ */
+public class LuhnTest {
+
+    public LuhnTest() {
+    }
+
+    @Test
+    public void testComputeCheckDigit() {
+        String testString = "7992739871";
+        int checkNumber = Luhn.computeCheckDigit(testString, false);
+        System.out.println(checkNumber);
+        assertTrue(checkNumber == 3);
+    }
+
+    @Test
+    public void testValidateNumber() {
+        assertFalse(Luhn.validateNumber("79927398710"));
+        assertFalse(Luhn.validateNumber("79927398711"));
+        assertFalse(Luhn.validateNumber("79927398712"));
+        assertTrue(Luhn.validateNumber("79927398713"));
+        assertFalse(Luhn.validateNumber("79927398714"));
+        assertFalse(Luhn.validateNumber("79927398715"));
+        assertFalse(Luhn.validateNumber("79927398716"));
+        assertFalse(Luhn.validateNumber("79927398717"));
+        assertFalse(Luhn.validateNumber("79927398718"));
+        assertFalse(Luhn.validateNumber("79927398719"));
+    }
+
+}
+
+/**
+ * History:
+ *
+ * $$Log$$
+ *
+ */