Add proper message when wrong log level is sent

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

@@ -22,10 +22,12 @@
 import org.springframework.boot.actuate.endpoint.LoggersEndpoint.LoggerLevels;
 import org.springframework.boot.context.properties.ConfigurationProperties;
 import org.springframework.boot.logging.LogLevel;
+import org.springframework.http.HttpStatus;
 import org.springframework.http.ResponseEntity;
 import org.springframework.web.bind.annotation.PathVariable;
 import org.springframework.web.bind.annotation.RequestBody;
 import org.springframework.web.bind.annotation.ResponseBody;
+import org.springframework.web.bind.annotation.ResponseStatus;
 
 /**
  * Adapter to expose {@link LoggersEndpoint} as an {@link MvcEndpoint}.
@@ -74,7 +76,7 @@ public Object set(@PathVariable String name,
 			return ResponseEntity.ok().build();
 		}
 		catch (IllegalArgumentException ex) {
-			return ResponseEntity.badRequest().build();
+			throw new InvalidLogLevelException("No such log level " + configuration.get("configuredLevel"));
 		}
 	}
 
@@ -83,4 +85,17 @@ private LogLevel getLogLevel(Map<String, String> configuration) {
 		return (level == null ? null : LogLevel.valueOf(level.toUpperCase()));
 	}
 
+	/**
+	 * Exception thrown when the specified log level cannot be found.
+	 */
+	@SuppressWarnings("serial")
+	@ResponseStatus(value = HttpStatus.BAD_REQUEST, reason = "No such log level")
+	public static class InvalidLogLevelException extends RuntimeException {
+
+		public InvalidLogLevelException(String string) {
+			super(string);
+		}
+
+	}
+
 }

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

@@ -49,6 +49,7 @@
 import org.springframework.web.context.WebApplicationContext;
 
 import static org.hamcrest.Matchers.equalTo;
+import static org.hamcrest.Matchers.is;
 import static org.mockito.BDDMockito.given;
 import static org.mockito.Mockito.mock;
 import static org.mockito.Mockito.verify;
@@ -174,7 +175,8 @@ public void setLoggerWhenDisabledShouldReturnNotFound() throws Exception {
 	public void setLoggerWithWrongLogLevel() throws Exception {
 		this.mvc.perform(post("/loggers/ROOT").contentType(MediaType.APPLICATION_JSON)
 				.content("{\"configuredLevel\":\"other\"}"))
-				.andExpect(status().is4xxClientError());
+				.andExpect(status().is4xxClientError())
+				.andExpect(status().reason(is("No such log level")));
 		verifyZeroInteractions(this.loggingSystem);
 	}