Initial commit (#402).

src/main/java/org/gitlab4j/api/utils/EmailChecker.java

+package org.gitlab4j.api.utils;
+
+import java.util.regex.Pattern;
+
+public class EmailChecker {
+
+        /** Java regular expression for validating an email address. */
+        public static final String EMAIL_REGEX =
+                "(?:[a-z0-9!#$%&'*+/=?^_`{|}~-]+(?:\\.[a-z0-9!#$%&'*+/=?^_`{|}~-]+)*|\"(?:[\\x01-\\x08\\x0b\\x0c\\x0e-\\x1f\\x21\\x23-\\x5b\\x5d-\\x7f]|\\\\[\\x01-\\x09\\x0b\\x0c\\x0e-\\x7f])*\")@(?:(?:[a-z0-9](?:[a-z0-9-]*[a-z0-9])?\\.)+[a-z0-9](?:[a-z0-9-]*[a-z0-9])?|\\[(?:(?:25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)\\.){3}(?:25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?|[a-z0-9-]*[a-z0-9]:(?:[\\x01-\\x08\\x0b\\x0c\\x0e-\\x1f\\x21-\\x5a\\x53-\\x7f]|\\\\[\\x01-\\x09\\x0b\\x0c\\x0e-\\x7f])+)\\])";
+
+        /** Java Pattern instance for validating an email address. */
+        public static final Pattern EMAIL_REGEX_PATTERN = Pattern.compile(EMAIL_REGEX);
+
+        /**
+         * Returns true if the provided String is a valid email address.
+         *
+         * @param email the email address to check for validity
+         * @return true if the provided String is a valid email address, otherwise return false
+         */
+        public static final boolean isValidEmail(final String email) {
+            return (email == null ? false : EMAIL_REGEX_PATTERN.matcher(email).matches());
+        }
+}

src/test/java/org/gitlab4j/api/TestEmailChecker.java

+package org.gitlab4j.api;
+
+import static org.junit.Assert.assertFalse;
+import static org.junit.Assert.assertTrue;
+
+import org.gitlab4j.api.utils.EmailChecker;
+import org.junit.Test;
+
+public class TestEmailChecker {
+
+    @Test
+    public void testValidEmail() {
+        assertTrue(EmailChecker.isValidEmail("john@foobar.com"));
+    }
+
+    @Test
+    public void testValidEmailWithPeriods() {
+        assertTrue(EmailChecker.isValidEmail("john.doe@foobar.com"));
+    }
+
+    @Test
+    public void testMissingTld() {
+        assertFalse(EmailChecker.isValidEmail("john@foobar"));
+    }
+
+    @Test
+    public void testMissingHostname() {
+        assertFalse(EmailChecker.isValidEmail("sam@.com"));
+    }
+
+    @Test
+    public void testNameOnly() {
+        assertFalse(EmailChecker.isValidEmail("john"));
+    }
+
+    @Test
+    public void testNullEmail() {
+        assertFalse(EmailChecker.isValidEmail(null));
+    }
+
+    @Test
+    public void testEmptyEmail() {
+        assertFalse(EmailChecker.isValidEmail(""));
+    }
+}