Make the module dependency on java.logging optional

Currently, FlatLaf has the following module dependencies:

$ jdeps --list-deps --multi-release 9 flatlaf-1.0.jar
   java.base
   java.desktop
   java.logging

This commit makes the java.logging dependency optional and hides logging behind a facade that falls back to printing to stderr if the java.logging module is not available.

To test, create a reduced JRE with a command like

jdk-15/bin/jlink.exe --module-path jdk-15/jmods --add-modules java.desktop --add-modules java.instrument --output jre-15-desktop-only

(adding java.instrument, so the FlatLafDemo main class can be started from IntelliJ IDEA)

flatlaf-core/src/main/java/com/formdev/flatlaf/FlatLaf.java

@@ -38,8 +38,6 @@ import java.util.Properties;
 import java.util.ServiceLoader;
 import java.util.function.Consumer;
 import java.util.function.Function;
-import java.util.logging.Level;
-import java.util.logging.Logger;
 import javax.swing.BorderFactory;
 import javax.swing.Icon;
 import javax.swing.ImageIcon;
@@ -74,7 +72,6 @@ import com.formdev.flatlaf.util.UIScale;
 public abstract class FlatLaf
 	extends BasicLookAndFeel
 {
-	static final Logger LOG = Logger.getLogger( FlatLaf.class.getName() );
 	private static final String DESKTOPFONTHINTS = "awt.font.desktophints";
 
 	private static List<Object> customDefaultsSources;
@@ -103,7 +100,7 @@ public abstract class FlatLaf
 			UIManager.setLookAndFeel( newLookAndFeel );
 			return true;
 		} catch( Exception ex ) {
-			LOG.log( Level.SEVERE, "FlatLaf: Failed to initialize look and feel '" + newLookAndFeel.getClass().getName() + "'.", ex );
+			LoggingFacade.logSevere( "FlatLaf: Failed to initialize look and feel '" + newLookAndFeel.getClass().getName() + "'.", ex );
 			return false;
 		}
 	}
@@ -341,7 +338,7 @@ public abstract class FlatLaf
 			} else
 				aquaLaf = (BasicLookAndFeel) Class.forName( aquaLafClassName ).newInstance();
 		} catch( Exception ex ) {
-			LOG.log( Level.SEVERE, "FlatLaf: Failed to initialize Aqua look and feel '" + aquaLafClassName + "'.", ex );
+			LoggingFacade.logSevere( "FlatLaf: Failed to initialize Aqua look and feel '" + aquaLafClassName + "'.", ex );
 			throw new IllegalStateException();
 		}
 
@@ -577,7 +574,7 @@ public abstract class FlatLaf
 					.invoke( null, true );
 				defaults.put( key, value );
 			} catch( Exception ex ) {
-				Logger.getLogger( FlatLaf.class.getName() ).log( Level.SEVERE, null, ex );
+				LoggingFacade.logSevere( null, ex );
 				throw new RuntimeException( ex );
 			}
 		}
@@ -684,7 +681,7 @@ public abstract class FlatLaf
 				// update UI
 				updateUI();
 			} catch( UnsupportedLookAndFeelException ex ) {
-				LOG.log( Level.SEVERE, "FlatLaf: Failed to reinitialize look and feel '" + lookAndFeel.getClass().getName() + "'.", ex );
+				LoggingFacade.logSevere(  "FlatLaf: Failed to reinitialize look and feel '" + lookAndFeel.getClass().getName() + "'.", ex );
 			}
 		} );
 	}

flatlaf-core/src/main/java/com/formdev/flatlaf/IntelliJTheme.java

@@ -30,7 +30,6 @@ import java.util.HashSet;
 import java.util.List;
 import java.util.Map;
 import java.util.Set;
-import java.util.logging.Level;
 import javax.swing.UIDefaults;
 import javax.swing.plaf.ColorUIResource;
 import com.formdev.flatlaf.json.Json;
@@ -76,7 +75,7 @@ public class IntelliJTheme
 		try {
 		    return FlatLaf.install( createLaf( in ) );
 		} catch( Exception ex ) {
-			FlatLaf.LOG.log( Level.SEVERE, "FlatLaf: Failed to load IntelliJ theme", ex );
+			LoggingFacade.logSevere(  "FlatLaf: Failed to load IntelliJ theme", ex );
 		    return false;
 		}
 	}
@@ -324,7 +323,7 @@ public class IntelliJTheme
 				try {
 					uiValue = UIDefaultsLoader.parseValue( key, valueStr );
 				} catch( RuntimeException ex ) {
-					UIDefaultsLoader.logParseError( Level.CONFIG, key, valueStr, ex );
+					UIDefaultsLoader.logParseError( key, valueStr, ex, false );
 					return; // ignore invalid value
 				}
 			}

flatlaf-core/src/main/java/com/formdev/flatlaf/LinuxFontPolicy.java

@@ -28,7 +28,6 @@ import java.util.ArrayList;
 import java.util.Collections;
 import java.util.List;
 import java.util.StringTokenizer;
-import java.util.logging.Level;
 import com.formdev.flatlaf.util.StringUtils;
 import com.formdev.flatlaf.util.SystemInfo;
 import com.formdev.flatlaf.util.UIScale;
@@ -172,7 +171,7 @@ class LinuxFontPolicy
 				if( "1".equals( strs.get( 5 ) ) )
 					style |= Font.ITALIC;
 			} catch( RuntimeException ex ) {
-				FlatLaf.LOG.log( Level.CONFIG, "FlatLaf: Failed to parse 'font=" + generalFont + "'.", ex );
+				LoggingFacade.logConfig( "FlatLaf: Failed to parse 'font=" + generalFont + "'.", ex );
 			}
 		}
 
@@ -186,7 +185,7 @@ class LinuxFontPolicy
 				if( dpi < 50 )
 					dpi = 50;
 			} catch( NumberFormatException ex ) {
-				FlatLaf.LOG.log( Level.CONFIG, "FlatLaf: Failed to parse 'forceFontDPI=" + forceFontDPI + "'.", ex );
+				LoggingFacade.logConfig( "FlatLaf: Failed to parse 'forceFontDPI=" + forceFontDPI + "'.", ex );
 			}
 		}
 
@@ -225,7 +224,7 @@ class LinuxFontPolicy
 			while( (line = reader.readLine()) != null )
 				lines.add( line );
 		} catch( IOException ex ) {
-			FlatLaf.LOG.log( Level.CONFIG, "FlatLaf: Failed to read '" + filename + "'.", ex );
+			LoggingFacade.logConfig( "FlatLaf: Failed to read '" + filename + "'.", ex );
 		}
 		return lines;
 	}

flatlaf-core/src/main/java/com/formdev/flatlaf/LoggingFacade.java

@@ -0,0 +1,46 @@
+package com.formdev.flatlaf;
+
+import java.util.logging.Level;
+import java.util.logging.Logger;
+
+public class LoggingFacade
+{
+	private static final Logger LOG = createLogger();
+
+	private static Logger createLogger() {
+		try {
+			return Logger.getLogger( FlatLaf.class.getName() );
+		} catch( Throwable e ) {
+			// Module java.logging is not present
+			return null;
+		}
+	}
+
+	public static void logSevere( Throwable t ) {
+		logSevere( null, t );
+	}
+
+	public static void logSevere( String message ) {
+		logSevere( message, null );
+	}
+
+	public static void logSevere( String message, Throwable t ) {
+		if( LOG != null ) {
+			LOG.log( Level.SEVERE, message, t );
+		} else {
+			System.err.println( message );
+			t.printStackTrace();
+		}
+	}
+
+	public static void logConfig( String message, Throwable t ) {
+		if( LOG != null ) {
+			LOG.log( Level.CONFIG, message, t );
+		} else {
+			if (Boolean.getBoolean( "flatLaf.logConfig" )) {
+				System.err.println( message );
+				t.printStackTrace();
+			}
+		}
+	}
+}

flatlaf-core/src/main/java/com/formdev/flatlaf/UIDefaultsLoader.java

@@ -33,7 +33,6 @@ import java.util.Map;
 import java.util.Map.Entry;
 import java.util.Properties;
 import java.util.function.Function;
-import java.util.logging.Level;
 import javax.swing.UIDefaults;
 import javax.swing.UIManager;
 import javax.swing.UIDefaults.ActiveValue;
@@ -243,16 +242,21 @@ class UIDefaultsLoader
 				try {
 					defaults.put( key, parseValue( key, value, null, resolver, addonClassLoaders ) );
 				} catch( RuntimeException ex ) {
-					logParseError( Level.SEVERE, key, value, ex );
+					logParseError( key, value, ex, true );
 				}
 			}
 		} catch( IOException ex ) {
-			FlatLaf.LOG.log( Level.SEVERE, "FlatLaf: Failed to load properties files.", ex );
+			LoggingFacade.logSevere( "FlatLaf: Failed to load properties files.", ex );
 		}
 	}
 
-	static void logParseError( Level level, String key, String value, RuntimeException ex ) {
+	static void logParseError( String key, String value, RuntimeException ex, boolean severe ) {
-		FlatLaf.LOG.log( level, "FlatLaf: Failed to parse: '" + key + '=' + value + '\'', ex );
+		String message = "FlatLaf: Failed to parse: '" + key + '=' + value + '\'';
+		if (severe) {
+			LoggingFacade.logSevere( message, ex );
+		} else {
+			LoggingFacade.logConfig( message, ex );
+		}
 	}
 
 	static String resolveValue( String value, Function<String, String> propertiesGetter ) {
@@ -440,7 +444,7 @@ class UIDefaultsLoader
 			try {
 				return findClass( value, addonClassLoaders ).newInstance();
 			} catch( InstantiationException | IllegalAccessException | ClassNotFoundException ex ) {
-				FlatLaf.LOG.log( Level.SEVERE, "FlatLaf: Failed to instantiate '" + value + "'.", ex );
+				LoggingFacade.logSevere( "FlatLaf: Failed to instantiate '" + value + "'.", ex );
 				return null;
 			}
 		};
@@ -451,7 +455,7 @@ class UIDefaultsLoader
 			try {
 				return findClass( value, addonClassLoaders );
 			} catch( ClassNotFoundException ex ) {
-				FlatLaf.LOG.log( Level.SEVERE, "FlatLaf: Failed to find class '" + value + "'.", ex );
+				LoggingFacade.logSevere( "FlatLaf: Failed to find class '" + value + "'.", ex );
 				return null;
 			}
 		};
@@ -928,7 +932,7 @@ class UIDefaultsLoader
 
 		Object value = UIManager.get( uiKey );
 		if( value == null && !optional )
-			FlatLaf.LOG.log( Level.SEVERE, "FlatLaf: '" + uiKey + "' not found in UI defaults." );
+			LoggingFacade.logSevere( "FlatLaf: '" + uiKey + "' not found in UI defaults." );
 		return value;
 	}
 }

flatlaf-core/src/main/java/com/formdev/flatlaf/ui/JBRCustomDecorations.java

@@ -30,8 +30,6 @@ import java.awt.event.HierarchyListener;
 import java.beans.PropertyChangeListener;
 import java.lang.reflect.Method;
 import java.util.List;
-import java.util.logging.Level;
-import java.util.logging.Logger;
 import javax.swing.JDialog;
 import javax.swing.JFrame;
 import javax.swing.JRootPane;
@@ -40,6 +38,7 @@ import javax.swing.UIManager;
 import javax.swing.plaf.BorderUIResource;
 import com.formdev.flatlaf.FlatLaf;
 import com.formdev.flatlaf.FlatSystemProperties;
+import com.formdev.flatlaf.LoggingFacade;
 import com.formdev.flatlaf.util.HiDPIUtils;
 import com.formdev.flatlaf.util.SystemInfo;
 
@@ -155,7 +154,7 @@ public class JBRCustomDecorations
 		try {
 			return (Boolean) Window_hasCustomDecoration.invoke( window );
 		} catch( Exception ex ) {
-			Logger.getLogger( FlatLaf.class.getName() ).log( Level.SEVERE, null, ex );
+			LoggingFacade.logSevere( null, ex );
 			return false;
 		}
 	}
@@ -167,7 +166,7 @@ public class JBRCustomDecorations
 		try {
 			Window_setHasCustomDecoration.invoke( window );
 		} catch( Exception ex ) {
-			Logger.getLogger( FlatLaf.class.getName() ).log( Level.SEVERE, null, ex );
+			LoggingFacade.logSevere( null, ex );
 		}
 	}
 
@@ -181,7 +180,7 @@ public class JBRCustomDecorations
 			WWindowPeer_setCustomDecorationHitTestSpots.invoke( peer, hitTestSpots );
 			WWindowPeer_setCustomDecorationTitleBarHeight.invoke( peer, titleBarHeight );
 		} catch( Exception ex ) {
-			Logger.getLogger( FlatLaf.class.getName() ).log( Level.SEVERE, null, ex );
+			LoggingFacade.logSevere( null, ex );
 		}
 	}
 

flatlaf-core/src/main/java/com/formdev/flatlaf/util/JavaCompatibility.java

@@ -21,10 +21,8 @@ import java.awt.Graphics;
 import java.awt.Graphics2D;
 import java.lang.reflect.InvocationTargetException;
 import java.lang.reflect.Method;
-import java.util.logging.Level;
-import java.util.logging.Logger;
 import javax.swing.JComponent;
-import com.formdev.flatlaf.FlatLaf;
+import com.formdev.flatlaf.LoggingFacade;
 
 /**
  * Provides Java version compatibility methods.
@@ -58,7 +56,7 @@ public class JavaCompatibility
 						? new Class[] { JComponent.class, Graphics2D.class, String.class, int.class, float.class, float.class }
 						: new Class[] { JComponent.class, Graphics.class, String.class, int.class, int.class, int.class } );
 				} catch( Exception ex ) {
-					Logger.getLogger( FlatLaf.class.getName() ).log( Level.SEVERE, null, ex );
+					LoggingFacade.logSevere( ex );
 					throw new RuntimeException( ex );
 				}
 			}
@@ -70,7 +68,7 @@ public class JavaCompatibility
 			else
 				drawStringUnderlineCharAtMethod.invoke( null, c, g, text, underlinedIndex, x, y );
 		} catch( IllegalAccessException | IllegalArgumentException | InvocationTargetException ex ) {
-			Logger.getLogger( FlatLaf.class.getName() ).log( Level.SEVERE, null, ex );
+			LoggingFacade.logSevere( ex );
 			throw new RuntimeException( ex );
 		}
 	}
@@ -94,7 +92,7 @@ public class JavaCompatibility
 							: "clipStringIfNecessary",
 						new Class[] { JComponent.class, FontMetrics.class, String.class, int.class } );
 				} catch( Exception ex ) {
-					Logger.getLogger( FlatLaf.class.getName() ).log( Level.SEVERE, null, ex );
+					LoggingFacade.logSevere( ex );
 					throw new RuntimeException( ex );
 				}
 			}
@@ -103,7 +101,7 @@ public class JavaCompatibility
 		try {
 			return (String) getClippedStringMethod.invoke( null, c, fm, string, availTextWidth );
 		} catch( IllegalAccessException | IllegalArgumentException | InvocationTargetException ex ) {
-			Logger.getLogger( FlatLaf.class.getName() ).log( Level.SEVERE, null, ex );
+			LoggingFacade.logSevere( ex );
 			throw new RuntimeException( ex );
 		}
 	}

flatlaf-core/src/main/module-info/module-info.java

@@ -19,7 +19,7 @@
  */
 module com.formdev.flatlaf {
 	requires java.desktop;
-	requires java.logging;
+	requires static java.logging;
 
 	exports com.formdev.flatlaf;
 	exports com.formdev.flatlaf.icons;

flatlaf-intellij-themes/src/main/java/com/formdev/flatlaf/intellijthemes/Utils.java

@@ -17,25 +17,21 @@
 package com.formdev.flatlaf.intellijthemes;
 
 import java.io.IOException;
-import java.util.logging.Level;
-import java.util.logging.Logger;
-import com.formdev.flatlaf.FlatLaf;
 import com.formdev.flatlaf.IntelliJTheme;
+import com.formdev.flatlaf.LoggingFacade;
 
 /**
  * @author Karl Tauber
  */
 class Utils
 {
-	static final Logger LOG = Logger.getLogger( FlatLaf.class.getName() );
-
 	static IntelliJTheme loadTheme( String name ) {
 		try {
 			return new IntelliJTheme( Utils.class.getResourceAsStream(
 				"/com/formdev/flatlaf/intellijthemes/themes/" + name ) );
 		} catch( IOException ex ) {
 			String msg = "FlatLaf: Failed to load IntelliJ theme '" + name + "'";
-			LOG.log( Level.SEVERE, msg, ex );
+			LoggingFacade.logSevere( msg, ex );
 			throw new RuntimeException( msg, ex );
 		}
 	}

flatlaf-intellij-themes/src/main/java/com/formdev/flatlaf/intellijthemes/materialthemeuilite/Utils.java

@@ -17,25 +17,21 @@
 package com.formdev.flatlaf.intellijthemes.materialthemeuilite;
 
 import java.io.IOException;
-import java.util.logging.Level;
-import java.util.logging.Logger;
-import com.formdev.flatlaf.FlatLaf;
 import com.formdev.flatlaf.IntelliJTheme;
+import com.formdev.flatlaf.LoggingFacade;
 
 /**
  * @author Karl Tauber
  */
 class Utils
 {
-	static final Logger LOG = Logger.getLogger( FlatLaf.class.getName() );
-
 	static IntelliJTheme loadTheme( String name ) {
 		try {
 			return new IntelliJTheme( Utils.class.getResourceAsStream(
 				"/com/formdev/flatlaf/intellijthemes/themes/material-theme-ui-lite/" + name ) );
 		} catch( IOException ex ) {
 			String msg = "FlatLaf: Failed to load IntelliJ theme '" + name + "'";
-			LOG.log( Level.SEVERE, msg, ex );
+			LoggingFacade.logSevere( msg, ex );
 			throw new RuntimeException( msg, ex );
 		}
 	}