Use consistent 'ROOT' logger name

Ensure all LoggingSystem implementation provide a consistent ROOT logger
name. Prior to this commit the `/loggers` endpoint could return '' for
root loggers which could then not be set using a POST.

Fixes gh-7372

spring-boot/src/main/java/org/springframework/boot/logging/AbstractLoggingSystem.java

@@ -16,6 +16,7 @@
 
 package org.springframework.boot.logging;
 
+import java.util.Comparator;
 import java.util.HashMap;
 import java.util.LinkedHashSet;
 import java.util.Map;
@@ -35,6 +36,9 @@ import org.springframework.util.SystemPropertyUtils;
  */
 public abstract class AbstractLoggingSystem extends LoggingSystem {
 
+	protected static final Comparator<LoggerConfiguration> CONFIGURATION_COMPARATOR = new LoggerConfigurationComparator(
+			ROOT_LOGGER_NAME);
+
 	private final ClassLoader classLoader;
 
 	public AbstractLoggingSystem(ClassLoader classLoader) {

spring-boot/src/main/java/org/springframework/boot/logging/LoggerConfigurationComparator.java

@@ -25,9 +25,8 @@ import org.springframework.util.Assert;
  * Sorts the "root" logger as the first logger and then lexically by name after that.
  *
  * @author Ben Hale
- * @since 1.5.0
  */
-public class LoggerConfigurationComparator implements Comparator<LoggerConfiguration> {
+class LoggerConfigurationComparator implements Comparator<LoggerConfiguration> {
 
 	private final String rootLoggerName;
 
@@ -35,7 +34,7 @@ public class LoggerConfigurationComparator implements Comparator<LoggerConfigura
 	 * Create a new {@link LoggerConfigurationComparator} instance.
 	 * @param rootLoggerName the name of the "root" logger
 	 */
-	public LoggerConfigurationComparator(String rootLoggerName) {
+	LoggerConfigurationComparator(String rootLoggerName) {
 		Assert.notNull(rootLoggerName, "RootLoggerName must not be null");
 		this.rootLoggerName = rootLoggerName;
 	}

spring-boot/src/main/java/org/springframework/boot/logging/LoggingApplicationListener.java

@@ -350,7 +350,7 @@ public class LoggingApplicationListener implements GenericApplicationListener {
 	private void setLogLevel(LoggingSystem system, Environment environment, String name,
 			String level) {
 		try {
-			if (name.equalsIgnoreCase("root")) {
+			if (name.equalsIgnoreCase(LoggingSystem.ROOT_LOGGER_NAME)) {
 				name = null;
 			}
 			level = environment.resolvePlaceholders(level);

spring-boot/src/main/java/org/springframework/boot/logging/LoggingSystem.java

@@ -47,6 +47,13 @@ public abstract class LoggingSystem {
 	 */
 	public static final String NONE = "none";
 
+	/**
+	 * The name used to for the root logger. LoggingSystem implementations should ensure
+	 * that this is the name used to represent the root logger, regardless of the
+	 * underlying implementation.
+	 */
+	public static final String ROOT_LOGGER_NAME = "ROOT";
+
 	private static final Map<String, String> SYSTEMS;
 
 	static {
@@ -107,7 +114,8 @@ public abstract class LoggingSystem {
 
 	/**
 	 * Sets the logging level for a given logger.
-	 * @param loggerName the name of the logger to set
+	 * @param loggerName the name of the logger to set ({@code null} can be used for the
+	 * root logger).
 	 * @param level the log level
 	 */
 	public void setLogLevel(String loggerName, LogLevel level) {

spring-boot/src/main/java/org/springframework/boot/logging/java/JavaLoggingSystem.java

@@ -31,7 +31,6 @@ import org.springframework.boot.logging.AbstractLoggingSystem;
 import org.springframework.boot.logging.LogFile;
 import org.springframework.boot.logging.LogLevel;
 import org.springframework.boot.logging.LoggerConfiguration;
-import org.springframework.boot.logging.LoggerConfigurationComparator;
 import org.springframework.boot.logging.LoggingInitializationContext;
 import org.springframework.boot.logging.LoggingSystem;
 import org.springframework.util.Assert;
@@ -49,9 +48,6 @@ import org.springframework.util.StringUtils;
  */
 public class JavaLoggingSystem extends AbstractLoggingSystem {
 
-	private static final LoggerConfigurationComparator COMPARATOR = new LoggerConfigurationComparator(
-			"");
-
 	private static final LogLevels<Level> LEVELS = new LogLevels<Level>();
 
 	static {
@@ -122,8 +118,10 @@ public class JavaLoggingSystem extends AbstractLoggingSystem {
 	@Override
 	public void setLogLevel(String loggerName, LogLevel level) {
 		Assert.notNull(level, "Level must not be null");
-		String name = (StringUtils.hasText(loggerName) ? loggerName : "");
+		if (loggerName == null || ROOT_LOGGER_NAME.equals(loggerName)) {
-		Logger logger = Logger.getLogger(name);
+			loggerName = "";
+		}
+		Logger logger = Logger.getLogger(loggerName);
 		if (logger != null) {
 			logger.setLevel(LEVELS.convertSystemToNative(level));
 		}
@@ -136,7 +134,7 @@ public class JavaLoggingSystem extends AbstractLoggingSystem {
 		while (names.hasMoreElements()) {
 			result.add(getLoggerConfiguration(names.nextElement()));
 		}
-		Collections.sort(result, COMPARATOR);
+		Collections.sort(result, CONFIGURATION_COMPARATOR);
 		return Collections.unmodifiableList(result);
 	}
 
@@ -148,7 +146,9 @@ public class JavaLoggingSystem extends AbstractLoggingSystem {
 		}
 		LogLevel level = LEVELS.convertNativeToSystem(logger.getLevel());
 		LogLevel effectiveLevel = LEVELS.convertNativeToSystem(getEffectiveLevel(logger));
-		return new LoggerConfiguration(logger.getName(), level, effectiveLevel);
+		String name = (StringUtils.hasLength(logger.getName()) ? logger.getName()
+				: ROOT_LOGGER_NAME);
+		return new LoggerConfiguration(name, level, effectiveLevel);
 	}
 
 	private Level getEffectiveLevel(Logger root) {

spring-boot/src/main/java/org/springframework/boot/logging/log4j2/Log4J2LoggingSystem.java

@@ -41,7 +41,6 @@ import org.apache.logging.log4j.message.Message;
 import org.springframework.boot.logging.LogFile;
 import org.springframework.boot.logging.LogLevel;
 import org.springframework.boot.logging.LoggerConfiguration;
-import org.springframework.boot.logging.LoggerConfigurationComparator;
 import org.springframework.boot.logging.LoggingInitializationContext;
 import org.springframework.boot.logging.LoggingSystem;
 import org.springframework.boot.logging.Slf4JLoggingSystem;
@@ -61,9 +60,6 @@ import org.springframework.util.StringUtils;
  */
 public class Log4J2LoggingSystem extends Slf4JLoggingSystem {
 
-	private static final LoggerConfigurationComparator COMPARATOR = new LoggerConfigurationComparator(
-			LogManager.ROOT_LOGGER_NAME);
-
 	private static final String FILE_PROTOCOL = "file";
 
 	private static final LogLevels<Level> LEVELS = new LogLevels<Level>();
@@ -224,7 +220,7 @@ public class Log4J2LoggingSystem extends Slf4JLoggingSystem {
 		for (LoggerConfig loggerConfig : configuration.getLoggers().values()) {
 			result.add(convertLoggerConfiguration(loggerConfig));
 		}
-		Collections.sort(result, COMPARATOR);
+		Collections.sort(result, CONFIGURATION_COMPARATOR);
 		return result;
 	}
 
@@ -238,7 +234,11 @@ public class Log4J2LoggingSystem extends Slf4JLoggingSystem {
 			return null;
 		}
 		LogLevel level = LEVELS.convertNativeToSystem(loggerConfig.getLevel());
-		return new LoggerConfiguration(loggerConfig.getName(), level, level);
+		String name = loggerConfig.getName();
+		if (!StringUtils.hasLength(name) || LogManager.ROOT_LOGGER_NAME.equals(name)) {
+			name = ROOT_LOGGER_NAME;
+		}
+		return new LoggerConfiguration(name, level, level);
 	}
 
 	@Override
@@ -254,7 +254,9 @@ public class Log4J2LoggingSystem extends Slf4JLoggingSystem {
 	}
 
 	private LoggerConfig getLoggerConfig(String name) {
-		name = (StringUtils.hasText(name) ? name : LogManager.ROOT_LOGGER_NAME);
+		if (!StringUtils.hasLength(name) || ROOT_LOGGER_NAME.equals(name)) {
+			name = LogManager.ROOT_LOGGER_NAME;
+		}
 		return getLoggerContext().getConfiguration().getLoggers().get(name);
 	}
 

spring-boot/src/main/java/org/springframework/boot/logging/logback/LogbackLoggingSystem.java

@@ -41,7 +41,6 @@ import org.slf4j.impl.StaticLoggerBinder;
 import org.springframework.boot.logging.LogFile;
 import org.springframework.boot.logging.LogLevel;
 import org.springframework.boot.logging.LoggerConfiguration;
-import org.springframework.boot.logging.LoggerConfigurationComparator;
 import org.springframework.boot.logging.LoggingInitializationContext;
 import org.springframework.boot.logging.LoggingSystem;
 import org.springframework.boot.logging.Slf4JLoggingSystem;
@@ -59,9 +58,6 @@ import org.springframework.util.StringUtils;
  */
 public class LogbackLoggingSystem extends Slf4JLoggingSystem {
 
-	private static final LoggerConfigurationComparator COMPARATOR = new LoggerConfigurationComparator(
-			Logger.ROOT_LOGGER_NAME);
-
 	private static final String CONFIGURATION_FILE_PROPERTY = "logback.configurationFile";
 
 	private static final LogLevels<Level> LEVELS = new LogLevels<Level>();
@@ -219,7 +215,7 @@ public class LogbackLoggingSystem extends Slf4JLoggingSystem {
 		for (ch.qos.logback.classic.Logger logger : getLoggerContext().getLoggerList()) {
 			result.add(getLoggerConfiguration(logger));
 		}
-		Collections.sort(result, COMPARATOR);
+		Collections.sort(result, CONFIGURATION_COMPARATOR);
 		return result;
 	}
 
@@ -236,7 +232,11 @@ public class LogbackLoggingSystem extends Slf4JLoggingSystem {
 		LogLevel level = LEVELS.convertNativeToSystem(logger.getLevel());
 		LogLevel effectiveLevel = LEVELS
 				.convertNativeToSystem(logger.getEffectiveLevel());
-		return new LoggerConfiguration(logger.getName(), level, effectiveLevel);
+		String name = logger.getName();
+		if (!StringUtils.hasLength(name) || Logger.ROOT_LOGGER_NAME.equals(name)) {
+			name = ROOT_LOGGER_NAME;
+		}
+		return new LoggerConfiguration(name, level, effectiveLevel);
 	}
 
 	@Override
@@ -259,7 +259,9 @@ public class LogbackLoggingSystem extends Slf4JLoggingSystem {
 
 	private ch.qos.logback.classic.Logger getLogger(String name) {
 		LoggerContext factory = getLoggerContext();
-		name = (StringUtils.isEmpty(name) ? Logger.ROOT_LOGGER_NAME : name);
+		if (StringUtils.isEmpty(name) || ROOT_LOGGER_NAME.equals(name)) {
+			name = Logger.ROOT_LOGGER_NAME;
+		}
 		return factory.getLogger(name);
 
 	}

spring-boot/src/test/java/org/springframework/boot/logging/java/JavaLoggingSystemTests.java

@@ -33,6 +33,7 @@ import org.junit.Test;
 import org.springframework.boot.logging.AbstractLoggingSystemTests;
 import org.springframework.boot.logging.LogLevel;
 import org.springframework.boot.logging.LoggerConfiguration;
+import org.springframework.boot.logging.LoggingSystem;
 import org.springframework.boot.testutil.InternalOutputCapture;
 import org.springframework.util.ClassUtils;
 import org.springframework.util.StringUtils;
@@ -175,7 +176,7 @@ public class JavaLoggingSystemTests extends AbstractLoggingSystemTests {
 		List<LoggerConfiguration> configurations = this.loggingSystem
 				.getLoggerConfigurations();
 		assertThat(configurations).isNotEmpty();
-		assertThat(configurations.get(0).getName()).isEmpty();
+		assertThat(configurations.get(0).getName()).isEqualTo(LoggingSystem.ROOT_LOGGER_NAME);
 	}
 
 	@Test

spring-boot/src/test/java/org/springframework/boot/logging/log4j2/Log4J2LoggingSystemTests.java

@@ -40,6 +40,7 @@ import org.junit.Test;
 import org.springframework.boot.logging.AbstractLoggingSystemTests;
 import org.springframework.boot.logging.LogLevel;
 import org.springframework.boot.logging.LoggerConfiguration;
+import org.springframework.boot.logging.LoggingSystem;
 import org.springframework.boot.testutil.InternalOutputCapture;
 import org.springframework.boot.testutil.Matched;
 import org.springframework.util.FileCopyUtils;
@@ -148,7 +149,8 @@ public class Log4J2LoggingSystemTests extends AbstractLoggingSystemTests {
 		List<LoggerConfiguration> configurations = this.loggingSystem
 				.getLoggerConfigurations();
 		assertThat(configurations).isNotEmpty();
-		assertThat(configurations.get(0).getName()).isEmpty();
+		assertThat(configurations.get(0).getName())
+				.isEqualTo(LoggingSystem.ROOT_LOGGER_NAME);
 	}
 
 	@Test

spring-boot/src/test/java/org/springframework/boot/logging/logback/LogbackLoggingSystemTests.java

@@ -43,6 +43,7 @@ import org.springframework.boot.logging.LogFile;
 import org.springframework.boot.logging.LogLevel;
 import org.springframework.boot.logging.LoggerConfiguration;
 import org.springframework.boot.logging.LoggingInitializationContext;
+import org.springframework.boot.logging.LoggingSystem;
 import org.springframework.boot.testutil.InternalOutputCapture;
 import org.springframework.boot.testutil.Matched;
 import org.springframework.mock.env.MockEnvironment;
@@ -190,7 +191,7 @@ public class LogbackLoggingSystemTests extends AbstractLoggingSystemTests {
 				.getLoggerConfigurations();
 		assertThat(configurations).isNotEmpty();
 		assertThat(configurations.get(0).getName())
-				.isEqualTo(org.slf4j.Logger.ROOT_LOGGER_NAME);
+				.isEqualTo(LoggingSystem.ROOT_LOGGER_NAME);
 	}
 
 	@Test