Add /management endpoint provided via Spring Actuator

The new endpoint provide metrics including information about application environment, configuration, beans, caches via Spring Actuator. Additional custom endpoints for version info and statistics are available. The endpoint is protected by Spring Security and requires the admin role.

To allow monitoring of metrics, a Prometheus endpoint is provided via Micrometer.

The /management/health endpoint times out at the moment but this is caused by existing issues with beans for external services.

Web API documentation: https://docs.spring.io/spring-boot/docs/2.1.x/actuator-api/html/

Known issue:
Content type application/json may not be set for the Accept header of requests to the management API. Otherwise, only a JSON stub is returned. application/vnd.spring-boot.actuator.v2+json or */* should be used instead.

Refs #16 (closed).

src/main/java/de/thm/arsnova/config/AppConfig.java

@@ -26,6 +26,9 @@ import java.util.ArrayList;
 import java.util.List;
 import org.springframework.beans.factory.annotation.Autowired;
 import org.springframework.beans.factory.config.PropertiesFactoryBean;
+import org.springframework.boot.actuate.autoconfigure.endpoint.web.WebEndpointProperties;
+import org.springframework.boot.actuate.endpoint.http.ActuatorMediaType;
+import org.springframework.boot.autoconfigure.EnableAutoConfiguration;
 import org.springframework.boot.context.properties.EnableConfigurationProperties;
 import org.springframework.cache.CacheManager;
 import org.springframework.cache.annotation.EnableCaching;
@@ -69,7 +72,7 @@ import de.thm.arsnova.util.ImageUtils;
 import de.thm.arsnova.web.CacheControlInterceptorHandler;
 import de.thm.arsnova.web.CorsFilter;
 import de.thm.arsnova.web.DeprecatedApiInterceptorHandler;
-import de.thm.arsnova.web.PathApiVersionContentNegotiationStrategy;
+import de.thm.arsnova.web.PathBasedContentNegotiationStrategy;
 import de.thm.arsnova.web.ResponseInterceptorHandler;
 import de.thm.arsnova.websocket.ArsnovaSocketioServer;
 import de.thm.arsnova.websocket.ArsnovaSocketioServerImpl;
@@ -87,18 +90,23 @@ import de.thm.arsnova.websocket.ArsnovaSocketioServerImpl;
 		"de.thm.arsnova.cache",
 		"de.thm.arsnova.controller",
 		"de.thm.arsnova.event",
+		"de.thm.arsnova.management",
 		"de.thm.arsnova.security",
 		"de.thm.arsnova.service",
 		"de.thm.arsnova.web",
 		"de.thm.arsnova.websocket.handler"})
 @Configuration
 @EnableAsync(mode = AdviceMode.ASPECTJ)
+@EnableAutoConfiguration
 @EnableCaching(mode = AdviceMode.ASPECTJ)
 @EnableScheduling
 @EnableSpringConfigured
 @EnableWebMvc
 @PropertySource(
-		value = {"classpath:config/defaults.yml", "file:${arsnova.config-dir:.}/application.yml"},
+		value = {
+			"classpath:config/defaults.yml",
+			"classpath:config/actuator.yml",
+			"file:${arsnova.config-dir:.}/application.yml"},
 		ignoreResourceNotFound = true,
 		encoding = "UTF-8",
 		factory = YamlPropertySourceFactory.class
@@ -109,6 +117,7 @@ public class AppConfig implements WebMvcConfigurer {
 	public static final String API_V3_MEDIA_TYPE_VALUE = "application/vnd.de.thm.arsnova.v3+json";
 	public static final MediaType API_V2_MEDIA_TYPE = MediaType.valueOf(API_V2_MEDIA_TYPE_VALUE);
 	public static final MediaType API_V3_MEDIA_TYPE = MediaType.valueOf(API_V3_MEDIA_TYPE_VALUE);
+	public static final MediaType ACTUATOR_MEDIA_TYPE = MediaType.valueOf(ActuatorMediaType.V2_JSON);
 
 	@Autowired
 	private Environment env;
@@ -119,18 +128,22 @@ public class AppConfig implements WebMvcConfigurer {
 	@Autowired
 	private SecurityProperties securityProperties;
 
+	@Autowired
+	private WebEndpointProperties webEndpointProperties;
+
 	@Override
 	public void configureMessageConverters(final List<HttpMessageConverter<?>> converters) {
 		converters.add(defaultJsonMessageConverter());
 		converters.add(apiV2JsonMessageConverter());
+		converters.add(managementJsonMessageConverter());
 		converters.add(stringMessageConverter());
 		//converters.add(new MappingJackson2XmlHttpMessageConverter(builder.createXmlMapper(true).build()));
 	}
 
 	@Override
 	public void configureContentNegotiation(final ContentNegotiationConfigurer configurer) {
-		final PathApiVersionContentNegotiationStrategy strategy =
-				new PathApiVersionContentNegotiationStrategy(API_V3_MEDIA_TYPE);
+		final PathBasedContentNegotiationStrategy strategy =
+				new PathBasedContentNegotiationStrategy(API_V3_MEDIA_TYPE, webEndpointProperties.getBasePath());
 		configurer.mediaType("json", MediaType.APPLICATION_JSON_UTF8);
 		configurer.mediaType("xml", MediaType.APPLICATION_XML);
 		configurer.favorParameter(false);
@@ -228,6 +241,22 @@ public class AppConfig implements WebMvcConfigurer {
 		return converter;
 	}
 
+	@Bean
+	public MappingJackson2HttpMessageConverter managementJsonMessageConverter() {
+		final Jackson2ObjectMapperBuilder builder = new Jackson2ObjectMapperBuilder();
+		builder
+				.indentOutput(systemProperties.getApi().isIndentResponseBody())
+				.simpleDateFormat("yyyy-MM-dd'T'HH:mm:ssZ");
+		final ObjectMapper mapper = builder.build();
+		final MappingJackson2HttpMessageConverter converter = new MappingJackson2HttpMessageConverter(mapper);
+		final List<MediaType> mediaTypes = new ArrayList<>();
+		mediaTypes.add(ACTUATOR_MEDIA_TYPE);
+		mediaTypes.add(MediaType.APPLICATION_JSON_UTF8);
+		converter.setSupportedMediaTypes(mediaTypes);
+
+		return converter;
+	}
+
 	@Bean
 	public static PropertySourcesPlaceholderConfigurer propertySourcesPlaceholderConfigurer() {
 		final PropertySourcesPlaceholderConfigurer configurer = new PropertySourcesPlaceholderConfigurer();