Add Logger.subLogger methods

These methods allow to create a Logger instance
that is a child of another Logger instance.

Signed-off-by: Curtis Rueden <ctrueden@wisc.edu>

Author: maarzt

src/main/java/org/scijava/log/AbstractLogService.java

@@ -72,14 +72,7 @@ public AbstractLogService(final Properties properties) {
 			LogService.LOG_LEVEL_PROPERTY + ":");
 	}
 
-	// -- Logger methods --
-
-	@Override
-	public int getLevel() {
-		if (classAndPackageLevels.isEmpty()) return currentLevel;
-		return getLevelForClass(CallingClassUtils.getCallingClass().getName(),
-			currentLevel);
-	}
+	// -- AbstractLogService methods --
 
 	@Override
 	public void setLevel(final int level) {
@@ -91,11 +84,30 @@ public void setLevel(final String classOrPackageName, final int level) {
 		classAndPackageLevels.put(classOrPackageName, level);
 	}
 
+	// -- Logger methods --
+
 	@Override
 	public void alwaysLog(final int level, final Object msg, final Throwable t) {
 		rootLogger.alwaysLog(level, msg, t);
 	}
 
+	@Override
+	public String getName() {
+		return rootLogger.getName();
+	}
+
+	@Override
+	public int getLevel() {
+		if (classAndPackageLevels.isEmpty()) return currentLevel;
+		return getLevelForClass(CallingClassUtils.getCallingClass().getName(),
+			currentLevel);
+	}
+
+	@Override
+	public Logger subLogger(String nameExtension, int level) {
+		return rootLogger.subLogger(nameExtension, level);
+	}
+
 	// -- Listenable methods --
 
 	@Override
@@ -162,17 +174,12 @@ private Map<String, Integer> setupMapFromProperties(Properties properties,
 	private class RootLogger extends DefaultLogger {
 
 		public RootLogger() {
-			super(LogLevel.NONE);
+			super(AbstractLogService.this::notifyListeners, "", LogLevel.NONE);
 		}
 
 		@Override
 		public int getLevel() {
 			return AbstractLogService.this.getLevel();
 		}
-
-		@Override
-		protected void messageLogged(LogMessage message) {
-			AbstractLogService.this.notifyListeners(message);
-		}
 	}
 }

src/main/java/org/scijava/log/DefaultLogger.java

@@ -41,25 +41,31 @@
  * @author Curtis Rueden
  */
 @IgnoreAsCallingClass
-public class DefaultLogger implements Logger {
+public class DefaultLogger implements Logger, LogListener {
+
+	private final LogListener destination;
+
+	private final String name;
 
 	private final int level;
 
 	private final List<LogListener> listeners = new CopyOnWriteArrayList<>();
 
-	public DefaultLogger(final int level)
+	public DefaultLogger(final LogListener destination, final String name,
+								   final int level)
 	{
+		this.destination = destination;
+		this.name = name;
 		this.level = level;
 	}
 
-	// -- DefaultLogger methods --
+	// -- Logger methods --
 
-	protected void messageLogged(final LogMessage message) {
-		notifyListeners(message);
+	@Override
+	public String getName() {
+		return name;
 	}
 
-	// -- Logger methods --
-
 	@Override
 	public int getLevel() {
 		return level;
@@ -70,6 +76,10 @@ public void alwaysLog(final int level, final Object msg, final Throwable t) {
 		messageLogged(new LogMessage(level, msg, t));
 	}
 
+	public Logger subLogger(final String name, final int level) {
+		return new DefaultLogger(this, name, level);
+	}
+
 	// -- Listenable methods --
 
 	@Override
@@ -87,4 +97,13 @@ public void notifyListeners(final LogMessage message) {
 		for (LogListener listener : listeners)
 			listener.messageLogged(message);
 	}
+
+	// -- LogListener methods --
+
+	@Override
+	public void messageLogged(final LogMessage message) {
+		for (LogListener listener : listeners)
+			listener.messageLogged(message);
+		destination.messageLogged(message);
+	}
 }

src/main/java/org/scijava/log/Logger.java

@@ -163,7 +163,7 @@ default void log(final int level, final Throwable t) {
 
 	/**
 	 * Logs a message with an exception.
-	 * 
+	 *
 	 * @param level The level at which the information will be logged. If the
 	 *          current level (given by {@link #getLevel()} is below this one, no
 	 *          logging is performed.
@@ -184,6 +184,24 @@ default void log(final int level, final Object msg, final Throwable t) {
 	 */
 	void alwaysLog(int level, Object msg, Throwable t);
 
+	/** Returns the name of this logger. */
+	String getName();
+
 	/** Returns the log level of this logger. see {@link LogLevel} */
 	int getLevel();
+
+	/**
+	 * Creates a sub logger, that forwards the message it gets to this logger. The
+	 * sub logger will have the same log level as this logger.
+	 */
+	default Logger subLogger(String name) {
+		return subLogger(name, getLevel());
+	}
+
+	/**
+	 * Creates a sub logger, that forwards the message it gets to this logger.
+	 *
+	 * @param level The log level of the sub logger.
+	 */
+	Logger subLogger(String name, int level);
 }

src/test/java/org/scijava/log/DefaultLoggerTest.java

@@ -31,6 +31,7 @@
 
 package org.scijava.log;
 
+import static org.junit.Assert.assertFalse;
 import static org.junit.Assert.assertTrue;
 
 import org.junit.Before;
@@ -48,7 +49,7 @@ public class DefaultLoggerTest {
 
 	@Before
 	public void setup() {
-		logger = new DefaultLogger(LogLevel.INFO);
+		logger = new DefaultLogger(message -> {}, "", LogLevel.INFO);
 		listener = new TestLogListener();
 		logger.addListener(listener);
 	}
@@ -62,4 +63,30 @@ public void test() {
 		assertTrue(listener.hasLogged(m -> m.text().equals("Hello World!")));
 		assertTrue(listener.hasLogged(m -> m.level() == LogLevel.ERROR));
 	}
+
+	@Test
+	public void testSubLogger() {
+		listener.clear();
+		Logger sub = logger.subLogger("sub");
+
+		sub.error("Hello World!");
+
+		assertTrue(listener.hasLogged(m -> m.text().equals("Hello World!")));
+	}
+
+	@Test
+	public void testLogForwarding() {
+		listener.clear();
+		Logger sub = logger.subLogger("xyz");
+		TestLogListener subListener = new TestLogListener();
+		sub.addListener(subListener);
+
+		sub.error("Hello World!");
+		logger.error("Goodbye!");
+
+		assertTrue(subListener.hasLogged(m -> m.text().equals("Hello World!")));
+		assertFalse(subListener.hasLogged(m -> m.text().equals("Goodbye!")));
+		assertTrue(listener.hasLogged(m -> m.text().equals("Hello World!")));
+		assertTrue(listener.hasLogged(m -> m.text().equals("Goodbye!")));
+	}
 }

src/test/java/org/scijava/log/LogServiceTest.java

@@ -171,11 +171,14 @@ public void testListener() {
 		TestableLogService logService = new TestableLogService();
 		TestLogListener listener = new TestLogListener();
 		String msg1 = "Hello World!";
+		String msg2 = "foo bar";
 		// process
 		logService.addListener(listener);
 		logService.error(msg1);
+		logService.subLogger("xyz").debug(msg2);
 		// test
 		listener.hasLogged(m -> msg1.equals(m.text()));
+		listener.hasLogged(m -> msg2.equals(m.text()));
 	}
 
 	// -- Helper classes --