BAEL-3394 : Using headless mode in Java

core-java-modules/core-java-lang-2/src/main/java/com/baeldung/headlessmode/FlexibleApp.java

@@ -0,0 +1,27 @@
+package com.baeldung.headlessmode;
+
+import java.awt.GraphicsEnvironment;
+
+import javax.swing.JOptionPane;
+
+public class FlexibleApp {
+    public static final int HEADLESS = 0;
+    public static final int HEADED = 1;
+    public FlexibleApp() {
+
+        if (GraphicsEnvironment.isHeadless()) {
+            System.out.println("Hello World");
+        } else {
+            JOptionPane.showMessageDialog(null, "Hello World");
+        }
+
+    }
+    
+    public static int iAmFlexible() {
+        if (GraphicsEnvironment.isHeadless()) {
+            return HEADLESS;
+        } else {
+            return HEADED;
+        }
+    }
+}

core-java-modules/core-java-lang-2/src/test/java/com/baeldung/headlessmode/HeadlessModeUnitTest.java

@@ -0,0 +1,87 @@
+package com.baeldung.headlessmode;
+
+import static org.assertj.core.api.Assertions.assertThat;
+import static org.assertj.core.api.Assertions.assertThatExceptionOfType;
+
+import java.awt.Canvas;
+import java.awt.Font;
+import java.awt.FontMetrics;
+import java.awt.Frame;
+import java.awt.GraphicsEnvironment;
+import java.awt.HeadlessException;
+import java.awt.image.BufferedImage;
+import java.io.FileOutputStream;
+import java.io.IOException;
+import java.io.InputStream;
+
+import javax.imageio.ImageIO;
+
+import org.junit.Assume;
+import org.junit.Before;
+import org.junit.Test;
+
+public class HeadlessModeUnitTest {
+
+    private static final String IN_FILE = "/product.png";
+    private static final String OUT_FILE = System.getProperty("java.io.tmpdir") + "/product.jpg";
+    private static final String FORMAT = "jpg";
+
+    @Before
+    public void setUpHeadlessMode() {
+        System.setProperty("java.awt.headless", "true");
+    }
+
+    @Test
+    public void whenJavaAwtHeadlessSetToTrue_thenIsHeadlessReturnsTrue() {
+        assertThat(GraphicsEnvironment.isHeadless()).isTrue();
+    }
+
+    @Test
+    public void whenHeadlessMode_thenFontsWork() {
+        GraphicsEnvironment ge = GraphicsEnvironment.getLocalGraphicsEnvironment();
+
+        String fonts[] = ge.getAvailableFontFamilyNames();
+
+        assertThat(fonts).isNotEmpty();
+
+        Font font = new Font(fonts[0], Font.BOLD, 14);
+
+        FontMetrics fm = (new Canvas()).getFontMetrics(font);
+
+        assertThat(fm.getHeight()).isGreaterThan(0);
+        assertThat(fm.getAscent()).isGreaterThan(0);
+        assertThat(fm.getDescent()).isGreaterThan(0);
+    }
+
+    @Test
+    public void whenHeadlessMode_thenImagesWork() throws IOException {
+        boolean result = false;
+        try (InputStream inStream = HeadlessModeUnitTest.class.getResourceAsStream(IN_FILE); FileOutputStream outStream = new FileOutputStream(OUT_FILE)) {
+            BufferedImage inputImage = ImageIO.read(inStream);
+            result = ImageIO.write(inputImage, FORMAT, outStream);
+        }
+
+        assertThat(result).isTrue();
+    }
+
+    @Test
+    public void whenHeadlessmode_thenFrameThrowsHeadlessException() {
+        assertThatExceptionOfType(HeadlessException.class).isThrownBy(() -> {
+            Frame frame = new Frame();
+            frame.setVisible(true);
+            frame.setSize(120, 120);
+        });
+    }    
+
+    @Test
+    public void whenHeadless_thenFlexibleAppAdjustsItsBehavior() {
+        assertThat(FlexibleApp.iAmFlexible()).isEqualTo(FlexibleApp.HEADLESS);
+    }
+
+    @Test
+    public void whenHeaded_thenFlexibleAppAdjustsItsBehavior() {
+        Assume.assumeFalse(GraphicsEnvironment.isHeadless());
+        assertThat(FlexibleApp.iAmFlexible()).isEqualTo(FlexibleApp.HEADED);
+    }
+
+}