Ensure that Hypermedia-related auto-config works without Jackson

Previously, both HypermediaAutoConfiguration and HttpMessageConverters
assumed that if Spring HATEOAS was on the class path, then Jackson
would be too. When this was not the case, an application would fail
to start.

This commit updates both classes to back off appropriately when
Spring HATEOAS is on the classpath but Jackson is not.

Closes gh-7434

spring-boot-autoconfigure/src/main/java/org/springframework/boot/autoconfigure/hateoas/HypermediaAutoConfiguration.java

@@ -67,6 +67,7 @@ public class HypermediaAutoConfiguration {
 
 	@Configuration
 	@ConditionalOnMissingBean(LinkDiscoverers.class)
+	@ConditionalOnClass(ObjectMapper.class)
 	@EnableHypermediaSupport(type = HypermediaType.HAL)
 	protected static class HypermediaConfiguration {
 

spring-boot-autoconfigure/src/main/java/org/springframework/boot/autoconfigure/web/HttpMessageConverters.java

@@ -242,6 +242,9 @@ private static void addClassIfExists(List<Class<?>> list, String className) {
 		catch (ClassNotFoundException ex) {
 			// Ignore
 		}
+		catch (NoClassDefFoundError ex) {
+			// Ignore
+		}
 	}
 
 }

spring-boot-autoconfigure/src/test/java/org/springframework/boot/autoconfigure/hateoas/HypermediaAutoConfigurationWithoutJacksonTests.java

@@ -0,0 +1,55 @@
+/*
+ * Copyright 2012-2016 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.boot.autoconfigure.hateoas;
+
+import org.junit.Test;
+import org.junit.runner.RunWith;
+
+import org.springframework.boot.autoconfigure.ImportAutoConfiguration;
+import org.springframework.boot.autoconfigure.web.HttpMessageConvertersAutoConfiguration;
+import org.springframework.boot.autoconfigure.web.WebMvcAutoConfiguration;
+import org.springframework.boot.testutil.ClassPathExclusions;
+import org.springframework.boot.testutil.FilteredClassPathRunner;
+import org.springframework.mock.web.MockServletContext;
+import org.springframework.web.context.support.AnnotationConfigWebApplicationContext;
+
+/**
+ * Tests for {@link HypermediaAutoConfiguration} when Jackson is not on the classpath.
+ *
+ * @author Andy Wilkinson
+ */
+@RunWith(FilteredClassPathRunner.class)
+@ClassPathExclusions("jackson-*.jar")
+public class HypermediaAutoConfigurationWithoutJacksonTests {
+
+	private AnnotationConfigWebApplicationContext context;
+
+	@Test
+	public void jacksonRelatedConfigurationBacksOff() {
+		this.context = new AnnotationConfigWebApplicationContext();
+		this.context.register(BaseConfig.class);
+		this.context.setServletContext(new MockServletContext());
+		this.context.refresh();
+	}
+
+	@ImportAutoConfiguration({ HttpMessageConvertersAutoConfiguration.class,
+			WebMvcAutoConfiguration.class, HypermediaAutoConfiguration.class })
+	static class BaseConfig {
+
+	}
+
+}

spring-boot-autoconfigure/src/test/java/org/springframework/boot/autoconfigure/web/HttpMessageConvertersAutoConfigurationWithoutJacksonTests.java

@@ -0,0 +1,56 @@
+/*
+ * Copyright 2012-2016 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.boot.autoconfigure.web;
+
+import org.junit.After;
+import org.junit.Test;
+import org.junit.runner.RunWith;
+
+import org.springframework.boot.testutil.ClassPathExclusions;
+import org.springframework.boot.testutil.FilteredClassPathRunner;
+import org.springframework.context.annotation.AnnotationConfigApplicationContext;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+/**
+ * Tests for {@link HttpMessageConvertersAutoConfiguration} without Jackson on the
+ * classpath.
+ *
+ * @author Andy Wilkinson
+ */
+@RunWith(FilteredClassPathRunner.class)
+@ClassPathExclusions("jackson-*.jar")
+public class HttpMessageConvertersAutoConfigurationWithoutJacksonTests {
+
+	private AnnotationConfigApplicationContext context = new AnnotationConfigApplicationContext();
+
+	@After
+	public void close() {
+		if (this.context != null) {
+			this.context.close();
+		}
+	}
+
+	@Test
+	public void autoConfigurationWorksWithSpringHateosButWithoutJackson()
+			throws Exception {
+		this.context.register(HttpMessageConvertersAutoConfiguration.class);
+		this.context.refresh();
+		assertThat(this.context.getBeansOfType(HttpMessageConverters.class)).hasSize(1);
+	}
+
+}