ConsoleAppender: support JLine's org.jline.jansi.AnsiConsole for <withJansi>

logback-core/src/main/java/ch/qos/logback/core/ConsoleAppender.java

@@ -48,7 +48,11 @@ public class ConsoleAppender<E> extends OutputStreamAppender<E> {
     protected ConsoleTarget target = ConsoleTarget.SystemOut;
     protected boolean withJansi = false;
 
-    private final static String AnsiConsole_CLASS_NAME = "org.fusesource.jansi.AnsiConsole";
+    // Jansi was migrated from FuseSource (org.fusesource.jansi) to JLine (org.jline.jansi), which
+    // changed the package of AnsiConsole. Probe the JLine coordinates first, then fall back to the
+    // legacy FuseSource ones so that <withJansi> keeps working with both artifacts. See LOGBACK issue 1043.
+    private final static String[] ANSI_CONSOLE_CLASS_NAMES = { "org.jline.jansi.AnsiConsole",
+            "org.fusesource.jansi.AnsiConsole" };
     private final static String JANSI2_OUT_METHOD_NAME = "out";
     private final static String JANSI2_ERR_METHOD_NAME = "err";
     private final static String WRAP_SYSTEM_OUT_METHOD_NAME = "wrapSystemOut";
@@ -114,7 +118,7 @@ private OutputStream wrapWithJansi(OutputStream targetStream) {
         try {
             addInfo("Enabling JANSI AnsiPrintStream for the console.");
             ClassLoader classLoader = Loader.getClassLoaderOfObject(context);
-            Class<?> classObj = classLoader.loadClass(AnsiConsole_CLASS_NAME);
+            Class<?> classObj = loadAnsiConsoleClass(classLoader);
 
             Method systemInstallMethod  = classObj.getMethod(SYSTEM_INSTALL_METHOD_NAME);
             if(systemInstallMethod != null) {
@@ -157,6 +161,26 @@ private OutputStream wrapWithJansi(OutputStream targetStream) {
         return targetStream;
     }
 
+    /**
+     * Loads the Jansi {@code AnsiConsole} class, probing the candidate class names in
+     * {@link #ANSI_CONSOLE_CLASS_NAMES} order (JLine's {@code org.jline.jansi} first, then the legacy
+     * FuseSource {@code org.fusesource.jansi}). This keeps {@code <withJansi>} working across the Jansi
+     * migration from FuseSource to JLine.
+     *
+     * @throws ClassNotFoundException if none of the candidate classes is available.
+     */
+    Class<?> loadAnsiConsoleClass(ClassLoader classLoader) throws ClassNotFoundException {
+        ClassNotFoundException lastException = null;
+        for (String className : ANSI_CONSOLE_CLASS_NAMES) {
+            try {
+                return classLoader.loadClass(className);
+            } catch (ClassNotFoundException e) {
+                lastException = e;
+            }
+        }
+        throw lastException;
+    }
+
     /**
      * @return whether to use JANSI or not.
      */

logback-core/src/test/java/ch/qos/logback/core/ConsoleAppenderJansiClassResolutionTest.java

@@ -0,0 +1,76 @@
+/*
+ * Logback: the reliable, generic, fast and flexible logging framework.
+ * Copyright (C) 1999-2026, QOS.ch. All rights reserved.
+ *
+ * This program and the accompanying materials are dual-licensed under
+ * either the terms of the Eclipse Public License v2.0 as published by
+ * the Eclipse Foundation
+ *
+ *   or (per the licensee's choosing)
+ *
+ * under the terms of the GNU Lesser General Public License version 2.1
+ * as published by the Free Software Foundation.
+ */
+package ch.qos.logback.core;
+
+import org.junit.jupiter.api.Test;
+
+import java.util.HashMap;
+import java.util.Map;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertThrows;
+
+/**
+ * Verifies that {@link ConsoleAppender} probes the JLine Jansi {@code AnsiConsole} class name before
+ * the legacy FuseSource one, so that {@code <withJansi>} keeps working after the Jansi migration from
+ * FuseSource to JLine. See LOGBACK issue 1043.
+ */
+public class ConsoleAppenderJansiClassResolutionTest {
+
+    static final String JLINE = "org.jline.jansi.AnsiConsole";
+    static final String FUSESOURCE = "org.fusesource.jansi.AnsiConsole";
+
+    final ConsoleAppender<Object> ca = new ConsoleAppender<>();
+
+    /**
+     * ClassLoader that resolves only the AnsiConsole class names present in {@code known} (mapping each
+     * to a distinct stand-in class) and reports the others as absent.
+     */
+    private ClassLoader loaderResolving(Map<String, Class<?>> known) {
+        return new ClassLoader(getClass().getClassLoader()) {
+            @Override
+            public Class<?> loadClass(String name) throws ClassNotFoundException {
+                Class<?> mapped = known.get(name);
+                if (mapped != null) {
+                    return mapped;
+                }
+                if (JLINE.equals(name) || FUSESOURCE.equals(name)) {
+                    throw new ClassNotFoundException(name);
+                }
+                return super.loadClass(name);
+            }
+        };
+    }
+
+    @Test
+    public void prefersJLineWhenBothArePresent() throws ClassNotFoundException {
+        Map<String, Class<?>> known = new HashMap<>();
+        known.put(JLINE, String.class);
+        known.put(FUSESOURCE, Integer.class);
+        assertEquals(String.class, ca.loadAnsiConsoleClass(loaderResolving(known)));
+    }
+
+    @Test
+    public void fallsBackToFuseSourceWhenJLineIsAbsent() throws ClassNotFoundException {
+        Map<String, Class<?>> known = new HashMap<>();
+        known.put(FUSESOURCE, Integer.class);
+        assertEquals(Integer.class, ca.loadAnsiConsoleClass(loaderResolving(known)));
+    }
+
+    @Test
+    public void throwsWhenNoJansiIsAvailable() {
+        Map<String, Class<?>> none = new HashMap<>();
+        assertThrows(ClassNotFoundException.class, () -> ca.loadAnsiConsoleClass(loaderResolving(none)));
+    }
+}