Return log levels in /loggers endpoint payload

Update `LoggersEndpoint` to additionally return the log levels actually
supported by the system.

Fixes gh-7396

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

@@ -20,6 +20,9 @@ import java.util.Collection;
 import java.util.Collections;
 import java.util.LinkedHashMap;
 import java.util.Map;
+import java.util.NavigableSet;
+import java.util.Set;
+import java.util.TreeSet;
 
 import org.springframework.boot.context.properties.ConfigurationProperties;
 import org.springframework.boot.logging.LogLevel;
@@ -35,8 +38,7 @@ import org.springframework.util.Assert;
  * @since 1.5.0
  */
 @ConfigurationProperties(prefix = "endpoints.loggers")
-public class LoggersEndpoint
-		extends AbstractEndpoint<Map<String, LoggersEndpoint.LoggerLevels>> {
+public class LoggersEndpoint extends AbstractEndpoint<Map<String, Object>> {
 
 	private final LoggingSystem loggingSystem;
 
@@ -51,18 +53,31 @@ public class LoggersEndpoint
 	}
 
 	@Override
-	public Map<String, LoggerLevels> invoke() {
+	public Map<String, Object> invoke() {
 		Collection<LoggerConfiguration> configurations = this.loggingSystem
 				.getLoggerConfigurations();
 		if (configurations == null) {
 			return Collections.emptyMap();
 		}
-		Map<String, LoggerLevels> result = new LinkedHashMap<String, LoggerLevels>(
+		Map<String, Object> result = new LinkedHashMap<String, Object>();
+		result.put("levels", getLevels());
+		result.put("loggers", getLoggers(configurations));
+		return result;
+	}
+
+	private NavigableSet<LogLevel> getLevels() {
+		Set<LogLevel> levels = this.loggingSystem.getSupportedLogLevels();
+		return new TreeSet<LogLevel>(levels).descendingSet();
+	}
+
+	private Map<String, LoggerLevels> getLoggers(
+			Collection<LoggerConfiguration> configurations) {
+		Map<String, LoggerLevels> loggers = new LinkedHashMap<String, LoggerLevels>(
 				configurations.size());
 		for (LoggerConfiguration configuration : configurations) {
-			result.put(configuration.getName(), new LoggerLevels(configuration));
+			loggers.put(configuration.getName(), new LoggerLevels(configuration));
 		}
-		return result;
+		return loggers;
 	}
 
 	public LoggerLevels invoke(String name) {

spring-boot-actuator/src/test/java/org/springframework/boot/actuate/autoconfigure/EndpointAutoConfigurationTests.java

@@ -130,7 +130,9 @@ public class EndpointAutoConfigurationTests {
 	public void loggersEndpointHasLoggers() throws Exception {
 		load(CustomLoggingConfig.class, EndpointAutoConfiguration.class);
 		LoggersEndpoint endpoint = this.context.getBean(LoggersEndpoint.class);
-		Map<String, LoggerLevels> loggers = endpoint.invoke();
+		Map<String, Object> result = endpoint.invoke();
+		Map<String, LoggerLevels> loggers = (Map<String, LoggerLevels>) result
+				.get("loggers");
 		assertThat(loggers.size()).isGreaterThan(0);
 	}
 

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

@@ -17,6 +17,9 @@
 package org.springframework.boot.actuate.endpoint;
 
 import java.util.Collections;
+import java.util.EnumSet;
+import java.util.Map;
+import java.util.Set;
 
 import org.junit.Test;
 
@@ -45,12 +48,21 @@ public class LoggersEndpointTests extends AbstractEndpointTests<LoggersEndpoint>
 	}
 
 	@Test
+	@SuppressWarnings("unchecked")
 	public void invokeShouldReturnConfigurations() throws Exception {
 		given(getLoggingSystem().getLoggerConfigurations()).willReturn(Collections
 				.singletonList(new LoggerConfiguration("ROOT", null, LogLevel.DEBUG)));
-		LoggerLevels levels = getEndpointBean().invoke().get("ROOT");
-		assertThat(levels.getConfiguredLevel()).isNull();
-		assertThat(levels.getEffectiveLevel()).isEqualTo("DEBUG");
+		given(getLoggingSystem().getSupportedLogLevels())
+				.willReturn(EnumSet.allOf(LogLevel.class));
+		Map<String, Object> result = getEndpointBean().invoke();
+		Map<String, LoggerLevels> loggers = (Map<String, LoggerLevels>) result
+				.get("loggers");
+		Set<LogLevel> levels = (Set<LogLevel>) result.get("levels");
+		LoggerLevels rootLevels = loggers.get("ROOT");
+		assertThat(rootLevels.getConfiguredLevel()).isNull();
+		assertThat(rootLevels.getEffectiveLevel()).isEqualTo("DEBUG");
+		assertThat(levels).containsExactly(LogLevel.OFF, LogLevel.FATAL, LogLevel.ERROR,
+				LogLevel.WARN, LogLevel.INFO, LogLevel.DEBUG, LogLevel.TRACE);
 	}
 
 	public void invokeWhenNameSpecifiedShouldReturnLevels() throws Exception {

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

@@ -17,6 +17,7 @@
 package org.springframework.boot.actuate.endpoint.mvc;
 
 import java.util.Collections;
+import java.util.EnumSet;
 
 import org.junit.After;
 import org.junit.Before;
@@ -80,18 +81,23 @@ public class LoggersMvcEndpointTests {
 				.alwaysDo(MockMvcResultHandlers.print()).build();
 	}
 
+	@Before
 	@After
-	public void reset() {
+	public void resetMocks() {
 		Mockito.reset(this.loggingSystem);
+		given(this.loggingSystem.getSupportedLogLevels())
+				.willReturn(EnumSet.allOf(LogLevel.class));
 	}
 
 	@Test
 	public void getLoggerShouldReturnAllLoggerConfigurations() throws Exception {
 		given(this.loggingSystem.getLoggerConfigurations()).willReturn(Collections
 				.singletonList(new LoggerConfiguration("ROOT", null, LogLevel.DEBUG)));
+		String expected = "{\"levels\":[\"OFF\",\"FATAL\",\"ERROR\",\"WARN\",\"INFO\",\"DEBUG\",\"TRACE\"],"
+				+ "\"loggers\":{\"ROOT\":{\"configuredLevel\":null,\"effectiveLevel\":\"DEBUG\"}}}";
+		System.out.println(expected);
 		this.mvc.perform(get("/loggers")).andExpect(status().isOk())
-				.andExpect(content().string(equalTo("{\"ROOT\":{\"configuredLevel\":"
-						+ "null,\"effectiveLevel\":\"DEBUG\"}}")));
+				.andExpect(content().json(expected));
 	}
 
 	@Test