Add support for Spring HATEOAS hypermedia in Actuator endpoints

If spring-hateoas is on the classpath and an MvcEndpoint returns a
@ResponseBody it will be extended and wrapped into a Resource with links.
All the existing endpoints that return sensible JSON data can be extended
this way (i.e. not /logfile). The HAL browser will also be added as an
endpoint if available on the classpath. Finally, asciidocs for the
Actuator endpoints are available as a separate jar file, which if
included in an app will also generate a new (HTTP) endpoint.

Fixes gh-1390

spring-boot-samples/spring-boot-sample-hypermedia-gson/src/test/java/demo/SpringBootHypermediaApplicationTests.java

@@ -0,0 +1,61 @@
+package demo;
+
+import static org.springframework.test.web.servlet.request.MockMvcRequestBuilders.get;
+import static org.springframework.test.web.servlet.result.MockMvcResultMatchers.jsonPath;
+import static org.springframework.test.web.servlet.result.MockMvcResultMatchers.status;
+
+import org.junit.Before;
+import org.junit.Test;
+import org.junit.runner.RunWith;
+import org.springframework.beans.factory.annotation.Autowired;
+import org.springframework.boot.test.SpringApplicationConfiguration;
+import org.springframework.http.MediaType;
+import org.springframework.test.context.TestPropertySource;
+import org.springframework.test.context.junit4.SpringJUnit4ClassRunner;
+import org.springframework.test.context.web.WebAppConfiguration;
+import org.springframework.test.web.servlet.MockMvc;
+import org.springframework.test.web.servlet.setup.MockMvcBuilders;
+import org.springframework.web.context.WebApplicationContext;
+
+@RunWith(SpringJUnit4ClassRunner.class)
+@SpringApplicationConfiguration(classes = SpringBootHypermediaApplication.class)
+@WebAppConfiguration
+@TestPropertySource(properties="endpoints.health.sensitive: false")
+public class SpringBootHypermediaApplicationTests {
+
+	@Autowired
+	private WebApplicationContext context;
+
+	private MockMvc mockMvc;
+
+	@Before
+	public void setUp() {
+		this.mockMvc = MockMvcBuilders.webAppContextSetup(this.context).build();
+	}
+
+	@Test
+	public void health() throws Exception {
+		this.mockMvc
+		.perform(get("/health").accept(MediaType.APPLICATION_JSON))
+		.andExpect(status().isOk())
+		.andExpect(jsonPath("$.links[0].href").value("http://localhost/health"))
+		.andExpect(jsonPath("$.content.status").exists());
+	}
+
+	@Test
+	public void trace() throws Exception {
+		this.mockMvc
+		.perform(get("/trace").accept(MediaType.APPLICATION_JSON))
+		.andExpect(status().isOk())
+		.andExpect(jsonPath("$.links[0].href").value("http://localhost/trace"))
+		.andExpect(jsonPath("$.content").isArray());
+	}
+
+	@Test
+	public void envValue() throws Exception {
+		this.mockMvc.perform(get("/env/user.home").accept(MediaType.APPLICATION_JSON))
+		.andExpect(status().isOk())
+		.andExpect(jsonPath("$._links").doesNotExist());
+	}
+
+}