Add redirection to actuator endpoint

If a request to the actuator endpoint ends with a slash with Spring
HATEOAS on the classpath, an empty array of links is returned whereas
a request without the slash returns a response with all the expected
links to the actuator's other endpoints.

This commit adds an automatic redirection so that both URIs return the
expected result.

Closes gh-4575

spring-boot-actuator/src/main/java/org/springframework/boot/actuate/endpoint/mvc/HalJsonMvcEndpoint.java

@@ -87,6 +87,11 @@ public class HalJsonMvcEndpoint extends WebMvcConfigurerAdapter
 		return new ResourceSupport();
 	}
 
+	@RequestMapping(path = "/", produces = MediaType.APPLICATION_JSON_VALUE)
+	public String forward() {
+		return "redirect:" + this.managementServletContext.getContextPath() + this.path;
+	}
+
 	public void setPath(String path) {
 		this.path = path;
 	}

spring-boot-actuator/src/test/java/org/springframework/boot/actuate/endpoint/mvc/HalBrowserMvcEndpointManagementContextPathIntegrationTests.java

@@ -39,6 +39,7 @@ import org.springframework.web.context.WebApplicationContext;
 import static org.springframework.hateoas.mvc.ControllerLinkBuilder.linkTo;
 import static org.springframework.test.web.servlet.request.MockMvcRequestBuilders.get;
 import static org.springframework.test.web.servlet.result.MockMvcResultMatchers.forwardedUrl;
+import static org.springframework.test.web.servlet.result.MockMvcResultMatchers.header;
 import static org.springframework.test.web.servlet.result.MockMvcResultMatchers.jsonPath;
 import static org.springframework.test.web.servlet.result.MockMvcResultMatchers.status;
 
@@ -75,6 +76,13 @@ public class HalBrowserMvcEndpointManagementContextPathIntegrationTests {
 				.andExpect(status().isOk()).andExpect(jsonPath("$._links").exists());
 	}
 
+	@Test
+	public void redirectJson() throws Exception {
+		this.mockMvc.perform(get("/admin/").accept(MediaType.APPLICATION_JSON))
+				.andExpect(status().isFound())
+				.andExpect(header().string("location", "/admin"));
+	}
+
 	@Test
 	public void actuatorHomeHtml() throws Exception {
 		this.mockMvc.perform(get("/admin/").accept(MediaType.TEXT_HTML))

spring-boot-actuator/src/test/java/org/springframework/boot/actuate/endpoint/mvc/MvcEndpointIntegrationTests.java

@@ -124,7 +124,7 @@ public class MvcEndpointIntegrationTests {
 				"management.context-path:/management");
 		MockMvc mockMvc = createSecureMockMvc();
 		mockMvc.perform(get("/management/info")).andExpect(status().isOk());
-		mockMvc.perform(get("/management/")).andExpect(status().isOk());
+		mockMvc.perform(get("/management")).andExpect(status().isOk());
 	}
 
 	@Test