henhan · April 7, 2016 06:12 · Apr 7, 2016 · Apr 6, 2016
diff --git a/SwedishIdUtils.java b/SwedishIdUtils.java
@@ -4,7 +4,7 @@ public class SwedishIdUtils {
 
     public static boolean validateId(String id) {
         // Only allow digits, whitespace + and - (+ is sometimes used to indicate age greater than 100 years)
-        if (!id.matches("^[\\-\\s\\+\\d]+$")) {
+        if (id == null || !id.matches("^[\\-\\s\\+\\d]+$")) {
             return false;
         }
         // Remove all non digits

diff --git a/SwedishIdUtils.java b/SwedishIdUtils.java
@@ -0,0 +1,49 @@
+import java.util.Calendar;
+
+public class SwedishIdUtils {
+
+    public static boolean validateId(String id) {
+        // Only allow digits, whitespace + and - (+ is sometimes used to indicate age greater than 100 years)
+        if (!id.matches("^[\\-\\s\\+\\d]+$")) {
+            return false;
+        }
+        // Remove all non digits
+        String in = id.replaceAll("\\D", "");
+        if (in.length() != 10 && in.length() != 12) {
+            return false;
+        }
+        if (in.length() == 12) {
+            // Validate century prefix and reduce string that is to be validated to 10 digits
+            // Other prefixes than these indicate that it is a company
+            int prefix = Integer.parseInt(in.substring(0, 2));
+            if (prefix < 18 || prefix > 20) {
+                return false;
+            }
+            // Validate that year is not greater than current
+            int currentYear = Calendar.getInstance().get(Calendar.YEAR);
+            if (Integer.parseInt(in.substring(0, 4)) > currentYear) {
+                return false;
+            }
+            in = in.substring(2);
+        }
+        int sum = 0;
+        for (int i = 0; i < in.length(); i++) {
+            int value = Character.getNumericValue(in.charAt(i));
+            sum += getValidationValue(i, value);
+        }
+        return sum % 10 == 0;
+    }
+
+    private static int getValidationValue(int index, int baseValue) {
+        if (index % 2 != 0) {
+            return baseValue;
+        }
+        int doubled = 2 * baseValue;
+        if (doubled < 10) {
+            return doubled;
+        } else {
+            return 1 + (doubled - 10);
+        }
+    }
+
+}