Show logs in GUI

src/main/java/com/penapereira/example/constructs/app/properties/Messages.java

@@ -16,6 +16,7 @@ public class Messages {
 	protected String info;
 	protected String examplesFound;
 	protected String enableTraceToSeeExamplesDetails;
-	protected String enableDebugToSeeExamplesList;
-	protected String separator;
+        protected String enableDebugToSeeExamplesList;
+        protected String separator;
+        protected String outputTitle;
 }

src/main/java/com/penapereira/example/constructs/app/ui/GuiAppender.java

@@ -0,0 +1,30 @@
+package com.penapereira.example.constructs.app.ui;
+
+import java.awt.EventQueue;
+
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+import org.springframework.beans.factory.InitializingBean;
+import org.springframework.beans.factory.annotation.Autowired;
+import org.springframework.stereotype.Component;
+
+import ch.qos.logback.classic.spi.ILoggingEvent;
+import ch.qos.logback.core.AppenderBase;
+
+@Component
+public class GuiAppender extends AppenderBase<ILoggingEvent> implements InitializingBean {
+
+    @Autowired
+    private MainWindow mainWindow;
+
+    @Override
+    public void afterPropertiesSet() throws Exception {
+        ((ch.qos.logback.classic.Logger) LoggerFactory.getLogger(Logger.ROOT_LOGGER_NAME)).addAppender(this);
+        start();
+    }
+
+    @Override
+    protected void append(ILoggingEvent eventObject) {
+        EventQueue.invokeLater(() -> mainWindow.appendOutput(eventObject.getFormattedMessage() + System.lineSeparator()));
+    }
+}

src/main/java/com/penapereira/example/constructs/app/ui/MainWindow.java

@@ -3,14 +3,17 @@
 import java.awt.Color;
 import java.awt.Cursor;
 import java.awt.Font;
+import java.awt.BorderLayout;
 import java.awt.GridLayout;
 import java.io.IOException;
 
 import javax.imageio.ImageIO;
 import javax.swing.JFrame;
 import javax.swing.JLabel;
 import javax.swing.JPanel;
+import javax.swing.JScrollPane;
 import javax.swing.JSeparator;
+import javax.swing.JTextArea;
 import javax.swing.SwingConstants;
 
 import org.slf4j.Logger;
@@ -26,7 +29,9 @@ public class MainWindow extends JFrame {
 
 	private static final Logger log = LoggerFactory.getLogger(MainWindow.class);
 
-	private static final long serialVersionUID = 1L;
+        private static final long serialVersionUID = 1L;
+
+        private JTextArea outputArea;
 
 	@Autowired
 	Messages msg;
@@ -65,13 +70,23 @@ private void loadIcon() {
 		}
 	}
 
-	private JPanel getMainComponent() {
-		JPanel mainPanel = new JPanel(new GridLayout(4, 1));
-		createCenteredTitle(msg.getGreeting(), mainPanel);
-		createCenteredLabelOnPanel(msg.getInfo(), mainPanel);
-		createCenteredHyperlink(msg.getHomeUrl(), mainPanel);
-		return mainPanel;
-	}
+        private JPanel getMainComponent() {
+                JPanel mainPanel = new JPanel(new BorderLayout());
+
+                JPanel infoPanel = new JPanel(new GridLayout(4, 1));
+                createCenteredTitle(msg.getGreeting(), infoPanel);
+                createCenteredLabelOnPanel(msg.getInfo(), infoPanel);
+                createCenteredHyperlink(msg.getHomeUrl(), infoPanel);
+                mainPanel.add(infoPanel, BorderLayout.NORTH);
+
+                outputArea = new JTextArea(10, 40);
+                outputArea.setEditable(false);
+                JScrollPane scrollPane = new JScrollPane(outputArea);
+                scrollPane.setBorder(javax.swing.BorderFactory.createTitledBorder(msg.getOutputTitle()));
+                mainPanel.add(scrollPane, BorderLayout.CENTER);
+
+                return mainPanel;
+        }
 
 	private void createCenteredTitle(String text, JPanel panel) {
 		JLabel title = new JLabel(text, JLabel.CENTER);
@@ -89,10 +104,17 @@ private void createCenteredHyperlink(String text, JPanel panel) {
 		panel.add(hyperlink);
 	}
 
-	private void createCenteredLabelOnPanel(String text, JPanel panel) {
-		JLabel label = new JLabel(text);
-		label.setHorizontalAlignment(JLabel.CENTER);
-		panel.add(label);
-	}
+        private void createCenteredLabelOnPanel(String text, JPanel panel) {
+                JLabel label = new JLabel(text);
+                label.setHorizontalAlignment(JLabel.CENTER);
+                panel.add(label);
+        }
+
+        public void appendOutput(String text) {
+                if (outputArea != null) {
+                        outputArea.append(text);
+                        outputArea.setCaretPosition(outputArea.getDocument().getLength());
+                }
+        }
 
 }

src/main/resources/application.properties

@@ -18,5 +18,6 @@ msg.examplesFound=Implemented examples found
 
 msg.enableTraceToSeeExamplesDetails= [*] Please enable TRACE log level if you want to see examples output
 msg.enableDebugToSeeExamplesList= [*] Please enable DEBUG log level if you want to see the examples list
+msg.outputTitle=Output
 
 msg.separator=-------------------------------------------------------------

src/test/java/com/penapereira/example/constructs/app/properties/MessagesTests.java

@@ -16,6 +16,7 @@ void settersAndGettersWork() {
         m.setEnableTraceToSeeExamplesDetails("TD");
         m.setEnableDebugToSeeExamplesList("DL");
         m.setSeparator("-");
+        m.setOutputTitle("OT");
 
         assertEquals("G", m.getGreeting());
         assertEquals("T", m.getWindowTitle());
@@ -25,6 +26,7 @@ void settersAndGettersWork() {
         assertEquals("TD", m.getEnableTraceToSeeExamplesDetails());
         assertEquals("DL", m.getEnableDebugToSeeExamplesList());
         assertEquals("-", m.getSeparator());
+        assertEquals("OT", m.getOutputTitle());
 
         String s = m.toString();
         assertTrue(s.contains("G"));
@@ -40,6 +42,7 @@ void settersAndGettersWork() {
         other.setEnableTraceToSeeExamplesDetails("TD");
         other.setEnableDebugToSeeExamplesList("DL");
         other.setSeparator("-");
+        other.setOutputTitle("OT");
         assertEquals(m, other);
         assertEquals(m.hashCode(), other.hashCode());
         assertNotEquals(m, "foo");

src/test/java/com/penapereira/example/constructs/app/ui/GuiAppenderTests.java

@@ -0,0 +1,44 @@
+package com.penapereira.example.constructs.app.ui;
+
+import static org.junit.jupiter.api.Assertions.*;
+
+import java.awt.EventQueue;
+import java.lang.reflect.Field;
+
+import javax.swing.JTextArea;
+
+import org.junit.jupiter.api.Test;
+
+import ch.qos.logback.classic.Level;
+import ch.qos.logback.classic.spi.LoggingEvent;
+
+class GuiAppenderTests {
+    @Test
+    void appendsMessageToTextArea() throws Exception {
+        // Allocate a MainWindow instance without triggering the JFrame constructor
+        Field theUnsafeField = sun.misc.Unsafe.class.getDeclaredField("theUnsafe");
+        theUnsafeField.setAccessible(true);
+        sun.misc.Unsafe unsafe = (sun.misc.Unsafe) theUnsafeField.get(null);
+
+        MainWindow window = (MainWindow) unsafe.allocateInstance(MainWindow.class);
+        JTextArea area = new JTextArea();
+        Field f = MainWindow.class.getDeclaredField("outputArea");
+        f.setAccessible(true);
+        f.set(window, area);
+
+        GuiAppender appender = new GuiAppender();
+        Field mw = GuiAppender.class.getDeclaredField("mainWindow");
+        mw.setAccessible(true);
+        mw.set(appender, window);
+        appender.start();
+
+        LoggingEvent event = new LoggingEvent();
+        event.setLevel(Level.INFO);
+        event.setMessage("test message");
+
+        appender.doAppend(event);
+        EventQueue.invokeAndWait(() -> {});
+
+        assertEquals("test message" + System.lineSeparator(), area.getText());
+    }
+}