Restore the java.util.logging root handlers after an embedded execution

maven-executor/src/main/java/org/apache/maven/executor/embedded/EmbeddedMavenExecutor.java

@@ -44,6 +44,8 @@
 import java.util.concurrent.ConcurrentHashMap;
 import java.util.concurrent.atomic.AtomicBoolean;
 import java.util.function.Function;
+import java.util.logging.Handler;
+import java.util.logging.Logger;
 import java.util.stream.Stream;
 
 import org.apache.maven.executor.Executor;
@@ -146,6 +148,7 @@ public ExecutorResult execute(ExecutorRequest executorRequest) throws ExecutorEx
                     "Unknown command: '" + command + "' for '" + installationDirectory + "'");
         }
 
+        Handler[] rootLoggerHandlers = Logger.getLogger("").getHandlers();
         Thread.currentThread().setContextClassLoader(context.tccl);
         try {
             return exec.apply(executorRequest);
@@ -160,10 +163,27 @@ public ExecutorResult execute(ExecutorRequest executorRequest) throws ExecutorEx
                 System.setErr(originalStderr);
                 Thread.currentThread().setContextClassLoader(originalClassLoader);
                 System.setProperties(originalProperties);
+                restoreRootLoggerHandlers(rootLoggerHandlers);
             }
         }
     }
 
+    /**
+     * Maven 4 replaces the handlers of the {@code java.util.logging} root logger with jul-to-slf4j's
+     * {@code SLF4JBridgeHandler}, whose classes come from Maven's realm: left in place, it breaks every later
+     * {@code java.util.logging} record of this JVM once the realm is closed. Puts back the handlers the root logger had
+     * before the execution.
+     */
+    private static void restoreRootLoggerHandlers(Handler[] handlers) {
+        Logger root = Logger.getLogger("");
+        for (Handler handler : root.getHandlers()) {
+            root.removeHandler(handler);
+        }
+        for (Handler handler : handlers) {
+            root.addHandler(handler);
+        }
+    }
+
     @Override
     public String mavenVersion() throws ExecutorException {
         if (closed.get()) {

maven-executor/src/main/java9/module-info.java

@@ -18,6 +18,8 @@
  */
 
 module org.apache.maven.executor {
+    requires java.logging;
+
     exports org.apache.maven.executor;
     exports org.apache.maven.executor.forked;
     exports org.apache.maven.executor.embedded;

maven-executor/src/test/java/org/apache/maven/executor/embedded/EmbeddedJulHandlersTest.java

@@ -0,0 +1,77 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *   http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ * KIND, either express or implied.  See the License for the
+ * specific language governing permissions and limitations
+ * under the License.
+ */
+package org.apache.maven.executor.embedded;
+
+import java.nio.file.Files;
+import java.nio.file.Path;
+import java.nio.file.Paths;
+import java.util.Arrays;
+import java.util.List;
+import java.util.logging.Handler;
+import java.util.logging.Logger;
+
+import org.apache.maven.executor.Environment;
+import org.apache.maven.executor.ExecutorRequest;
+import org.apache.maven.executor.ExecutorResult;
+import org.junit.jupiter.api.Timeout;
+import org.junit.jupiter.api.io.TempDir;
+import org.junit.jupiter.params.ParameterizedTest;
+import org.junit.jupiter.params.provider.ValueSource;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertTrue;
+
+/**
+ * Maven 4 installs jul-to-slf4j's {@code SLF4JBridgeHandler} on the {@code java.util.logging} root logger of the JVM it
+ * runs in. Embedded, that is the caller's JVM, and the handler's classes live in Maven's class realm: once the
+ * executor closes that realm, every later {@code java.util.logging} record of the caller fails with
+ * {@code NoClassDefFoundError: org/slf4j/spi/LocationAwareLogger}.
+ */
+@Timeout(120)
+class EmbeddedJulHandlersTest {
+    @TempDir
+    Path temp;
+
+    @ParameterizedTest
+    @ValueSource(strings = {"3", "4"})
+    void rootLoggerHandlersAreRestored(String maven) throws Exception {
+        Path home = Paths.get("3".equals(maven) ? Environment.MAVEN3_HOME : Environment.MAVEN4_HOME);
+        Path cwd = Files.createDirectories(temp.resolve("cwd"));
+        Logger root = Logger.getLogger("");
+        List<Handler> before = Arrays.asList(root.getHandlers());
+
+        try (EmbeddedMavenExecutor executor = new EmbeddedMavenExecutor(home)) {
+            ExecutorResult result = executor.execute(ExecutorRequest.mavenBuilder()
+                    .cwd(cwd)
+                    .userHomeDirectory(temp)
+                    .argument("-v")
+                    .grabOutputAsString(true)
+                    .build());
+            assertTrue(
+                    result.success(),
+                    () -> result.stdOutString().orElse("")
+                            + result.stdErrString().orElse(""));
+            assertEquals(before, Arrays.asList(root.getHandlers()), "root handlers after an execution");
+        }
+
+        assertEquals(before, Arrays.asList(root.getHandlers()), "root handlers after close");
+        // must not throw NoClassDefFoundError from a handler of the closed realm
+        Logger.getLogger(EmbeddedJulHandlersTest.class.getName()).warning("logged after embedded Maven " + maven);
+    }
+}