Improve JNDI detection logic

Update JndiLocatorDelegate.isDefaultJndiEnvironmentAvailable() to
call `getEnvironment()` on the `InitialContext` in order to actually
trigger a NamingException if JNDI is not available.

Issue: SPR-12223

spring-context/src/main/java/org/springframework/jndi/JndiLocatorDelegate.java

@@ -58,7 +58,7 @@ public class JndiLocatorDelegate extends JndiLocatorSupport {
 	 */
 	public static boolean isDefaultJndiEnvironmentAvailable() {
 		try {
-			new InitialContext();
+			new InitialContext().getEnvironment();
 			return true;
 		}
 		catch (Throwable ex) {

spring-context/src/test/java/org/springframework/jndi/JndiLocatorDelegateTests.java

@@ -0,0 +1,37 @@
+/*
+ * Copyright 2002-2014 the original author or authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.springframework.jndi;
+
+import org.junit.Test;
+
+import static org.hamcrest.Matchers.*;
+
+import static org.junit.Assert.*;
+
+/**
+ * Tests for {@link JndiLocatorDelegate}.
+ *
+ * @author Phillip Webb
+ */
+public class JndiLocatorDelegateTests {
+
+	@Test
+	public void isDefaultJndiEnvironmentAvailableFalse() {
+		assertThat(JndiLocatorDelegate.isDefaultJndiEnvironmentAvailable(), equalTo(false));
+	}
+
+}