Add FreeMarker support

This commit adds auto-configuration and a starter,
spring-boot-starter-freemarker, for using FreeMarker view templates in
a web application.

A new abstraction, TemplateAvailabilityProvider, has been introduced.
This decouples ErrorMvcAutoConfiguration from the various view
technologies that Spring Boot now supports, allowing it to determine
when a custom error template is provided without knowing the details of
each view technology.

Closes #679

spring-boot-samples/spring-boot-sample-web-freemarker/src/test/java/sample/freemarker/SampleWebFreeMarkerApplicationTests.java

@@ -0,0 +1,76 @@
+/*
+ * Copyright 2012-2014 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 sample.freemarker;
+
+import java.util.Arrays;
+
+import org.junit.Test;
+import org.junit.runner.RunWith;
+import org.springframework.boot.test.IntegrationTest;
+import org.springframework.boot.test.SpringApplicationConfiguration;
+import org.springframework.boot.test.TestRestTemplate;
+import org.springframework.http.HttpEntity;
+import org.springframework.http.HttpHeaders;
+import org.springframework.http.HttpMethod;
+import org.springframework.http.HttpStatus;
+import org.springframework.http.MediaType;
+import org.springframework.http.ResponseEntity;
+import org.springframework.test.annotation.DirtiesContext;
+import org.springframework.test.context.junit4.SpringJUnit4ClassRunner;
+import org.springframework.test.context.web.WebAppConfiguration;
+
+import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertTrue;
+
+/**
+ * Basic integration tests for FreeMarker application.
+ *
+ * @author Phillip Webb
+ * @author Andy Wilkinson
+ */
+@RunWith(SpringJUnit4ClassRunner.class)
+@SpringApplicationConfiguration(classes = SampleWebFreeMarkerApplication.class)
+@WebAppConfiguration
+@IntegrationTest
+@DirtiesContext
+public class SampleWebFreeMarkerApplicationTests {
+
+	@Test
+	public void testFreeMarkerTemplate() throws Exception {
+		ResponseEntity<String> entity = new TestRestTemplate().getForEntity(
+				"http://localhost:8080", String.class);
+		assertEquals(HttpStatus.OK, entity.getStatusCode());
+		assertTrue("Wrong body:\n" + entity.getBody(),
+				entity.getBody().contains("Hello, Andy"));
+	}
+
+	@Test
+	public void testFreeMarkerErrorTemplate() throws Exception {
+		HttpHeaders headers = new HttpHeaders();
+		headers.setAccept(Arrays.asList(MediaType.TEXT_HTML));
+		HttpEntity<String> requestEntity = new HttpEntity<String>(headers);
+
+		ResponseEntity<String> responseEntity = new TestRestTemplate().exchange(
+				"http://localhost:8080/does-not-exist", HttpMethod.GET, requestEntity,
+				String.class);
+
+		assertEquals(HttpStatus.NOT_FOUND, responseEntity.getStatusCode());
+		assertTrue("Wrong body:\n" + responseEntity.getBody(), responseEntity.getBody()
+				.contains("Something went wrong: 404 Not Found"));
+	}
+
+}