Create an endpoint for creating country lists #15

src/main/java/org/eclipsefoundation/geoip/client/helper/CountryHelper.java

+/**
+ * Copyright (c) 2021 Eclipse Foundation
+ *
+ * This program and the accompanying materials are made
+ * available under the terms of the Eclipse Public License 2.0
+ * which is available at https://www.eclipse.org/legal/epl-2.0/
+ *
+ * Author: Martin Lowe <martin.lowe@eclipse-foundation.org>
+ *
+ * SPDX-License-Identifier: EPL-2.0
+ */
+package org.eclipsefoundation.geoip.client.helper;
+
+import java.util.ArrayList;
+import java.util.HashMap;
+import java.util.List;
+import java.util.Locale;
+import java.util.Map;
+
+import org.eclipsefoundation.geoip.client.model.ISOCountry;
+
+/**
+ * Helper to retrieve and cache countries and country codes in a light manner.
+ */
+public class CountryHelper {
+    private static final Map<String, List<ISOCountry>> countryListCache = new HashMap<>();
+
+    public static List<ISOCountry> getCountries(Locale l) {
+        // Default to EN locale if not specified
+        Locale actualLocale = l != null ? l : Locale.ENGLISH;
+        // get the cached data if it exists
+        List<ISOCountry> countries = countryListCache.get(actualLocale.getLanguage());
+        if (countries == null) {
+            // generate cached data
+            String[] isoCountries = Locale.getISOCountries();
+            countries = new ArrayList<>(isoCountries.length);
+            for (String isoCountry : isoCountries) {
+                Locale c = new Locale("", isoCountry);
+                countries.add(new ISOCountry(c.getDisplayCountry(actualLocale), c.getCountry()));
+            }
+            countryListCache.put(actualLocale.getLanguage(), countries);
+        }
+        return new ArrayList<>(countries);
+    }
+
+    private CountryHelper() {
+    }
+}